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The Journal of
Raptor ResearchVolume 36 Number 4 December 2002
Published by
The Raptor Research Foundation* Inc
THE RAPTOR RESEARCH FOUNDATION, INC.
(Founded 1966)
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EDITOR: James C. Bednarz, Department of Biological Sciences, P.O. Box 599, Arkansas State
University, State University, AR 72467 U.S.A.
ASSOCIATE EDITORS
James R. BeithoffClint W. Boai.
Joan L. MorrisonJuan Jose Negro
Marco Resiani
Ian G. WarkentinTroy I. Wellicome
BOOK REVIEW EDITOR: Jeffreys. Marks, Montana Cooperative Research Unit, University of Montana,Missoula, MT 59812 U.S.A.
SPANISH EDITOR: Cesar Marquez Reyes, Instituto Humboldt, Colombia, AA. 094766, Bogota 8, ColombiaEDITORIAL ASSISTANTS: Rebecca S. Maul, Kristina Baker, Joan Clark
The Journal of Raptor Research is distributed quarterly to all current members. Original manuscripts
dealing with the biology and conservation of diurnal and nocturnal birds of prey are welcomed fromthroughout the world, but must be written in English. Submissions can be in the form of research articles,
short communications, letters to the editor, and book reviews. Contributors should submit a typewritten
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should be centered on the cover page. If the current address is different, indicate this via a footnote. Ashort version of the title, not exceeding 35 characters, should be provided for a running head. Anabstract of about 250 words should accompany all research articles on a separate page.
Tables, one to a page, should be double-spaced throughout and be assigned consecutive Arabic numer-als. Collect all figure legends on a separate page. Each illustration should be centered on a single pageand be no smaller than final size and no larger than twice final size. The name of the author (s) and figure
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Names for birds should follow the A.O.U. Checklist of North American Birds (7th ed., 1998) or another
authoritative source for other regions. Subspecific identification should be cited only when pertinent to
the material presented. Metric units should be used for all measurements. Use the 24-hour clock (e.g.,
0830 H and 2030 H) and “continental” dating (e.g., 1 January 1999).
Refer to a recent issue of the journal for details in format. Explicit instructions and publication policy
are outlined in “Information for contributors , Raptor Res., Vol. 36(4), and are available from the editor.
Submit manuscripts to J. Bednarz at the address listed above.
COVER: Bald Eagles {Haliaeetus leucocephalus)
.
Painting byJohn Schmitt.
ContentsForaging Ecology of Nesting Bald Eagles in Arizona, w. Grainger Hunt, Ronald e.
Jackman, Daniel E. Driscoll, and Edward W. Bianchi 245
Vernal Migration of Bald Eagles from a Southern Colorado Wintering Area.
Alan R. Harmata 256
Does Northern Goshawk Breeding Occupancy Vary with Nest-stand Character-
istics ON THE Olympic Peninsula, Washington? Sean p. Finn, Daniel e. Variand, and
John M. Marzluff 265
Subordinate Males Sire Offspring in Madagascar Fish-Eagle {Hauaeetus vocife-
ROIDES) PoLYANDROUS BREEDING GROUPS. Ruth E. Tingay, Melanie Culver, Eric M.
Hallerman, James D. Fraser, and Richard T. Watson 280
Nesting and Perching Habitat Use of the Madagascar Fish-Eagle. James Berkeiman,
James D. Fraser, and Richard T Watson 287
Use of Vegetative Structure by Powerful Owls in Outer Urban Melbourne,
Victoria, Australia—Implications for Management. Rayiene Cooke, Robert Waiiis,
andJohn White 294
Nest-site Selection of the Crowned Hawk-Eagle in the Forests of Kwazulu-
NATAL, South Africa, and TaI, Ivory Coast. Gerard Malan and Susanne Shultz 300
Short Communications
Juvenile Dispersal of Madagascar Fish-Eagles Tracked by Satellite Telemetry. Simon
Rafanomezantsoa, Richard T. Watson, and Russell Thorstrom 309
Prey of the Peregrine Falcon (Falco Peregiunus cassini) in Southern Argentina and Chile. David
H. Ellis, Beth Ann Sabo, James K. Tackier, and Brian A. Millsap 315
An Elevated Net Assembly to Capture Nesting Raptors. Eugene A. Jacobs and Glenn A. Proudfoot 320
Florida Bald Eagle {Hauaeetus leucocephalus) Egg Characteristics. M. Alan Jenkins, Steve KSherrod, David A. Wiedenfeld, and Donald H. Wolfe, Jr. 324
Osprey Ecology in the Mangroves of Southeastern Brazil. Robson Silva e Silva and Fabio Olmos 328
Diet of Breeding Tropical Screech-Owls (Otus chouba) in Southeastern Brazil. Jose Carlos
Mottajunior 332
Letters
Comments of the First Nesting Record of the Nest of a Slaty-backed Forest Falcon {Micrastur
MIRANDOUEJ) IN THE ECUADORIAN AMAZON. Russell Thorstrom 335
Micrastur or Acupiter, That is the Question. Tjitte de Vries and Cristian Melo 337
Book Reviews. Edited byJeffery S. Marks 338
Information For Contributors 340
Index to Volume 36 344
The Raptor Research Foundation, Inc. gratefully acknowledges funds and logistical supportprovided by Arkansas State University to assist in the publication of the journal.
THE JOURNAL OF RAPTOR RESEARCHA QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.
VoL. 36 December 2002 No. 4
/. Raptor Res. 36(4):245-255
© 2002 The Raptor Research Foundation, Inc.
FORAGING ECOLOGY OF NESTING BALD EAGLES IN ARIZONA
W. Grainger Hunt/ Ronald E. Jackman, and Daniel E. DriscollPredatory Bird Research Group, Long Marine Laboratory,
University of California, Santa Cruz, CA 93060 U.S.A.
Edward W. BianchiEntrix, 7919 Folsom Blvd., Suite 100, Sacramento, CA 93826 U.S.A.
Abstract.—^We studied foraging ecology of nesting Bald Eagles (Haliaeetus leucocephalus) in Arizona
during 1987-89, with emphasis on the influence of dams and river flow regulation. We examined diet,
foraging modes, habitat selection, fish abundance, and factors associated with fish availability. Based onbiomass, prey remains yielded 76% fish, 14% mammals, and 10% birds. On rivers, eagles primarily
caught live fish as they spawned or foraged in shallow water, whereas, on reservoirs, most fish were
obtained as carrion or as they floated moribund on the surface. Fish communities differed among river
reaches and reservoirs, and ecological and life-history characteristics influenced vulnerability and sea-
sonal differences in exploitation, Water temperature, a principal factor determining fish communitystructure among eagle territories, was also associated with temporal differences in fish availability, as was
flow and turbidity. Few prey sources remained constant throughout the reproductive cycle, and prey
and habitat diversity buffered temporal changes in prey availability. We conclude that dams benefit
breeding eagles to the extent that they create water temperature discontinuities and additional aquatic
habitats, some that support large populations of fish. However, environments modified by dams are not
necessarily better for Bald Eagles than those on free-flowing sections of rivers; our data show that Bald
Eagle reproduction in the two settings is nearly identical.
Key Words: Bald Eagle, Haliaeetus leucocephalus; dams; habitat selection; home range, piscivory; radiotelem-
etry; rivers.
ECOLOGIA DEL FORRAJEO DE AGUILAS CALVAS NIDIFICANDO EN ARIZONA
Resumen.—Estudiamos la ecologia de forrajeo de aguilas calvas {Haliaeetus leucocephalus) nidificando enArizona durante 1987-89, con enfasis en la influencia de los embalses y la regulacion del flujo de los
rios. Examinamos la dieta, modos de forrajeo, seleccion de habitat, abundancia de peces, y factores
asociados con la disponibilidad de peces. Tomando como base la biomasa, los restos de presas arrojaron
76% peces, 14% mamiferos, y 10% aves. En los rios, las aguilas ante todo capturaron peces vivos cuandoestos desovaban o forrajeaban en aguas someras, mientras que, en los reservorios, la mayoria del pescado
fue obtenido como carrona o cuando flotaban moribundos sobre la superficie. Las comunidades de
peces difirieron entre los limites de los rios y las caracteristicas ecologicas y de su historia de vida las
cuales influyeron en la vulnerabilidad y las diferencias estacionales en la explotacion. La temperatura
del agua, un factor primordial determinante de la estructura de la comunidad ictica entre los territorios
de las aguilas, fue asociada ademas con las diferencias temporales en disponibilidad de peces, tal comolo fue con el flujo y la turbidez. Pocos recursos de presas permanecieron constantes a traves de todo el
ciclo reproductivo, y las presas y diversidad de habitats amortiguaron los cambios temporales en la
disponibilidad de presas. Concluimos que los embalses benefician las aguilas que estan reproduciendose
en el sentido en que crean discontinuidades en la temperatura y habitats acuaticos adicionales, algunos
^ Present address: The Peregrine Fund, 5568 West Flying Hawk Lane, Boise, ID 83709 U.S.A.; e-mail address:
245
246 Hunt et al. VoL. 36, No. 4
de los cuales soportan grandes poblaciones de peces. Sin embargo, los ambientes modificados por las
represas no son necesariaraente mejores para las aguilas pescadoras que aquellos que estan en secciones
de libre flujo en los rios; nuestros datos muestran que la reproduccion de las aguilas pescadores en los
dos escenarios son cercanamente identicos.
[Traduccion de Cesar Marquez]
Population persistence in raptors and other ter-
ritorial birds depends on an aggregate of breeding
locations that contribute to above-replacement-rate
reproduction (Hunt and Law 2000). Conserving
high-quality sites requires knowledge of key com-
ponents, some being physiographic, others de-
pending on the ecology, behavior, and life-history
characteristics of associated biota. Of particular in-
terest are factors relating to food acquisition. Re-
productive success requires that breeding pairs
have sustained access to prey within efficient com-
muting distance (Royama 1970). For species with
prolonged breeding cycles (ca. 5 mo for North
American eagles), during which numerous phe-
nological events transpire, food continuity may in-
volve switching from one prey type to another over
the course of the nesting season (Jamieson et al.
1982, Edwards 1988).
Prey remains collected from nests of inland-
breeding Bald Eagles {Haliaeetus leucocephalus) of-
ten show dietary diversity. This has been observed
not only for populations as a whole, but for indi-
vidual nests (Todd et al. 1982,Jackman et al. 1999).
Thus, it is tempting to hypothesize that prey variety
and, by inference, environmental variation within
the foraging range are important components of
Bald Eagle territories in some regions (Grubb
1995).
From January 1987-June 1989, we investigated
the effects of dams and flow regulation on the nest-
ing population of Bald Eagles in central Arizona
(Driscoll et al. 1999). We obtained information onthe spatial and temporal aspects of foraging. Werecorded shifts of eagle prey use, foraging behav-
ior, and ranging patterns that followed temporal
variation in factors influencing prey availability. Wefound that water temperature and clarity, the struc-
ture of various riverine and lacustrine habitats, and
life-histories and behavior of prey species were in-
terrelated with respect to food availability.
Study Area
General Description. Our study centered on Bald Ea-
gle breeding territories along the Salt and Verde rivers
in central Arizona (Fig. 1), a generally open, desert land-
scape of the Upper and Lower Sonoran Life-Zones (Lowe
1964, Brown 1998). Eagles nested at elevations ranging
from ,329-1719 mask Riparian environments in these re-
gions are composed of Sonoran Riparian Deciduous For-
est and Woodlands Biome, Sonoran Riparian Scrubland
Biome, and the Sonoran Interior Strands Biome. Up-lands in the Lower Sonoran Life Zone are all within Son-
oran Desertscrub Biome (Brown 1998). Upper SonoranLife Zone (Brown 1998) vegetative composition near
Bald Eagle breeding territories includes Great Basin Co-
nifer Woodland, Interior Chaparral, and Semidesert
Grassland Biomes. Mean annual precipitation ranges
from 39 cm at higher elevations to 25 cm in the low
desert where temperatures may reach 50°C.
The central Arizona landscape has been greatly altered
by human activity. Cattle grazing, particularly after railway
development in the late 1800s, resulted in dramatic ero-
sion (Hastings 1959, Hastings and Turner 1965, Hayden1965). This and woodcutting reduced riparian forests to
a scattering of isolated groves and trees. Soil loss drained
near-surface aquifers, creating drier soil conditions, andlivers became muddy torrents following rains. With the
increased need for flood control, water storage, and ir-
rigation, hve impoundments were constructed on the
Salt River and two on the Verde River during the early
1900s. Riverine environments downstream of the reser-
voirs were changed by flow regulation and sediment fil-
tration, and upstream by migrations of fish populations
such as common carp {Cyprinus carpio) and catfish (Ic-
taluridae) out of the reservoirs.
Fisheries. Three native species of fish, appropriate for
eagle exploitation, remain in substantial numbers within
the study area: desert sucker {Catostomus insignis), Sonora
sucker (C. clarki), and roundtail chub {Gila robusta)
(Minckley 1973). Introduced species of potential impor-
tance to eagles in rivers and/or reservoirs include chan-
nel catfish {Ictalurus punctaLus), bullhead {Ameiurus ne-
bulosus and A. natalis), flathead catfish {Pylodictis olivaris)
,
common carp, black crappie {Pomoxis nigromaculatus)
,
yellow bass (Morone mississippiensis)
,
largemouth bass {Mi-
cropterus salmoides), smallniouth bass {M. dolomieui), blue-
gill {Lepomis macwchirus)
,
green sunfish {L. cyanellus),
and walleye (Stizostedion vitreum).
Fish distribution in central Arizona, as elsewhere, is
strongly influenced by water temperature (Vannote et al
1980, this study). Trout (Salmonidae) inhabit cool head-
waters. Suckers, smallmouth hass, and then channel cat-
fish increase in abundance as water warms downstreamWith increasing water temperature, carp and catfish be-
come the primary species in size categories suitable for
Bald Eagle foraging. When a river enters a reservoir, per-
ciforms (hass, perch, and crappie) predominate, al-
though carp and catfish cemtribute importantly to overall
fish biomass in the reservoir. Water temperature and vol-
ume released from the reservoir influence the fish com-munity below the dam. Cool releases from the hypolim-
nion of deep, stratified reservoirs favor sucker
populations. If the reservoir is shallow or unstable and
December 2002 Bald Eagle Foraging Ecology 247
Figure 1. The Salt and Verde river systems of central Arizona. The six names in italics identify breeding territories
where Bald Eagle foraging was studied with radio telemetry.
fails to maintain a cool hypolimnion, or if releases issue
from the epilimnion, warm releases favor carp and catfish
in the river reach below the dam. During spring, spawn-
ing runs of carp and catfish from downstream reservoirs
may augment riverine fish populations.
Study Sites. We studied Bald Eagle foraging at six
breeding territories (defined here to include the forag-
ing range) chosen to compare regulated with unregulat-
ed (i.e., free-flowing) environments (Fig. 1). All six ter-
ritories have been occupied by eagles since the 1970s
(Driscoll et al. 1999). Two breeding territories (Ladders
and East Verde) were on free-flowing rivers far from res-
ervoirs. Two other pairs (Bardett and Blue Point) occu-
pied settings in which all flows were regulated by damreleases, i.e., reservoirs releasing cold water and fed by
other dams upstream. The remaining two breeding ter-
ritories (Horseshoe and Pinal) included both reservoir
systems and the free-flowing rivers that fed them.
Methods
Telemetry. We used radio-controlled bow nets, powersnares, and noosed fish (Jackman et al. 1993, 1994) to
capture territorial eagles for radio-tagging. We attached
65-g transmitters with a backpack configuration of teflon
ribbons adjoined with cotton string over the carina to
permit eventual loss of the radio (Hunt et al. 1992,
McClelland et al. 1994). Mercury (activity) switches
changed the pulse rate when tilted from near-vertical to
horizontal (Kenward 2001). We refined signal interpre-
tation on the basis of frequent visual verification.
From the early brooding period to fledging, tracking
teams collected data in 8-d sessions separated by 6-d pe-
riods of no data collection. The objective was to obtain
uninterrupted, minute-by-minute records (time lines) of
movements and activities of radio-tagged eagles. To over-
come the bias associated with observer location, trackers
spread out to strategic viewing sites and maintained com-
248 Hunt et al. VoL. 36, No. 4
munication by hand-held radios. Tracking teams of three
to five members later conferred to eliminate duplicate
data points. To reference eagle locations, habitat vari-
ables, and prey, we marked river centerlines and reservoir
shorelines depicted on USGS topographic maps to show1-km and 0.1-km intervals. If we could not identify the
eagle’s location to the level of even a 1-km segment, wemarked the location within larger zones positioned be-
tween familiar landmarks.
We measured variables at prey-strike points as soon as
possible after a foraging event but without disturbing the
eagle. Recorded information included attack methodand aquatic habitat type, as follows: “pools” are depres-
sions in the streambed, with hydrologic control in the
downstream end and low current velocities relative to
prevailing streamflow; “runs” are moderately deep, usu-
ally narrow channels with relatively fast current, but little
or no white water; “riffles” are characterized by shallow,
fast-moving water flowing down gradients and over sub-
strates usually no larger than small boulders; “pocket wa-
ter” usually contains larger boulders, with fast water in-
terspersed across the width of the stream among frequent
pockets of quiet water; “cascades” are steep gradient
white water with less than 10% quiet water (Hunt et al.
1992). Microhabitat features measured at strike points in-
cluded water depth, water temperature, and turbidity
(Secchi disk). We collected evidence (e.g., scales) of prey
species identity, and estimated prey size and whether it
was obtained alive or as carrion.
Prey Delivery, Observers recorded prey deliveries to
the nests from points permitting clear views of nest bowls
and at distances of 125-400 m, typically beginning whenyoung were 2-3 wk of age. Prey items were assigned to
general taxonomic categories (e.g., class), then to morespecific categories (e.g., family, species), where possible.
For fish, diagnostic features included fin and scale char-
acteristics, body and mouth shapes, jaw configurations,
barbel presence, caudal peduncle thickness, and mark-
ings. Observers noted their confidence in each identifi-
cation; items identified with low confidence were as-
signed to a higher taxonomic level. We sometimes
confirmed identification with body parts (e.g., scales) col-
lected at eagle foraging sites. We did not distinguish be-
tween desert and Sonora suckers. We estimated prey size
by comparing the item with the length of the eagle’s bill
or with objects of known size in the nest.
Analysis of Tracking Data. Time line tracking data con-
sisted of 22 742 records of the movements and activities
ol nine radio-tagged adults in six breeding territories, for
a mean of 2327 records per tagged eagle. We recorded
the number of minutes an eagle remained at a location
and the frequency of visits to each location. The first
mea.sure (time) offered a relatively poor estimate of area
use compared to relocation frequency. Consider an ex-
ample in which an eagle loafed for 146 min at a location
300 m downstream of the nest (in sight of the nest), then
flew 2 km upstream where it perched for 5 min at each
of three locations, some 200 m apart. At the last of these,
the eagle caught a fish, after which it returned to the
nest area where it spent 62 rain. Clearly, a time-based
assessment awards small significance to the foraging area
where the eagle spent only 2% of its time. By contrast,
the relocation-based appraisal recognized each of the 0.1-
km segments (or larger zones) where the eagle perched.
Weighting each location equally as a measure of use was
supported by our data: in 80% of observed foraging
events, the eagle perched within sight of the foraging
location just before the event, and in 70% of cases, the
eagle appeared to have seen the prey before leaving the
perch.
Each perching visit to a O.Tkm segment received a
score of one point. If the eagle left a location and en-
tered another O.l-km segment along the river, but then
returned to the original location, the latter received an-
other point. Segments visited repeatedly thereby received
the most points. The large number of nest visits over-
shadowed other relocation scores; however, eliminating
the nest area from the analysis was inappropriate because
the nest vicinity was often an important foraging area.
Therefore, we used the prey delivery data to estimate the
percentage of foraging events occurring in the nest vicin-
ity. This became the relocation percentage for the nest
area, and percentages for all other areas within the homerange were adjusted accordingly so the total was 100%.
Collection and Analysis of Prey Remains. Collection. Wecollected prey remains within and below nests at five of
the six breeding territories studied (one nest was on an
inaccessible pinnacle) and at 16 other breeding sites in
Arizona. Collections occurred during the middle to late
part of the brood-rearing period and again after the
young had fledged. We attributed variation in the
amount of remains present to removal by the adults (ob-
served) and to the activities of woodrats (Neotoma spp.)
and other scavengers. We collected ca. 2 L of fine nest
lining from each nest for scale analysis to detect soft-
boned fish (e.g., trout, chub) (Jackman et al. 1999).
Analysis. We collected 5—10 individuals of differing sizes
of each fish species expected to occur in the eagles’ diet.
We weighed and measured each fish, then parboiled it
to remove all flesh. We weighed, dried, and labeled all
bones for reference.
We developed regression equations to relate bonelength to total body length for each species (Hunt et al.
1992, Jackman et al. 1999). Because unattached bones
were often from the same fish, we used the following
procedure to avoid duplication: first, we determined the
95% confidence intervals from each equation to deter-
mine the probable range of total length represented by
the bones. For a given collection and species, we calcu-
lated fish total length from each bone and then sorted
all like bones. Bones with the most entries and relatively
low confidence intervals were examined first. Wegrouped pairs of these bones of the same size (<1.0 mmdifference or <5 mm for broken bones), e.g., left andright opercula. We marked each pair and the remaining
odd entries as individual prey items. We next matchedthe opcrcula(s) from one fish with other bones whoseconfidence intervals for total body lengths overlapped
with those computed from the opercula. Because differ-
ent parts of the same fish had specific proportional re-
lationships (e.g,, ±2.0 mm for sucker opercula and clav-
icles), we eliminated those entries that were eclipsed by
the confidence intervals, a procedure that left the fewest
numbers of unmatched parts and, thus, the fewest pos-
sible number of individual fish represented. Results un-
December 2002 Baed Eagi.e Foraging Ecology 249
derestimated total fish numbers to the extent that
matched parts may have been from different fish.
We calculated total mass for the selected (nondupli-
cate) fish prey items, using length-to-mass equations fromthis study and from Carlander (1969, 1977) and Becker
(1983). We subtracted the mass of bones and scales
(from regression equations) plus 5% of total mass (esti-
mated unavailable biomass) to calculate the edible bio-
mass for each prey item. We identified nonfish remains
from museum reference collections and then used stan-
dard body mass for each species less 10% for inedible
parts.
Fish Sampling. Objectives of fish sampling within eagle
territories were to identify: (1) relative abundance ofprey
fish, (2) seasonal changes in their distribution, with em-phasis on availability to eagles (e.g., fish moving into shal-
low water), (3) spawning and its effect on fish availability,
and (4) effects of water management on prey fish avail-
ability.
Fish abundance, activity, and distribution. We conducted
both roving and fixed-point visual surveys. In roving sur-
veys, one or two biologists (depending upon flow) walked
along the river bank, noting abundance and activity of
fish, aquatic habitat, depth, location (within standard 0.1-
km segment), and water temperature. We also observed
fish activity and behavior from fixed points. Prior to sur-
veying, we compiled information on fish communities in
the various river reaches, tributaries, and reservoirs, in-
cluding Arizona Game and Fish Department (AGFD)and U.S. Fish and Wildlife Service reports and field data
from D. Henrickson (AGFD), M. Jakle (U.S. Bureau of
Reclamation), and C. Zeibell (Arizona Cooperative Fish-
eries Unit)
.
To verify our observational data and to determine go-
nadal development, we sampled fish in representative
habitats with gill nets and throw nets, and occasionally by
snorkeling surveys. We removed all collected fish fromthe system, many of which were used in the prey refer-
ence series. We conducted an electrofishing survey at the
East Verde territory just after the eagle nesting season.
Aquatic habitat surveys. We surveyed aquatic habitat dis-
tribution in four of the six eagle territories. We mappedsections of rivers and tributaries within eagle home rang-
es into basic habitat units, including pools, runs, riffles,
pocket water, and cascades, as defined by Hunt et al.
(1992). We differentiated between two types of riffles:
channel-riffles, which become runs during moderate flow
increase, and bar-riffles which remain as riffles under a
variety of flows. Bar-riffles are characterized by the pres-
ence of a gravel/cobble bar oriented diagonally or per-
pendicularly to flow. As flow increases, water depth andvelocity increase only partially in bar-riffles, whereas the
amount of shallow water increases overall due to spread-
ing of water across the gravel/cobble bar. We mappedreservoirs according to distributions of shallow water ar-
eas. We obtained river flow and reservoir water surface
elevation data from agencies maintaining gaging stations.
Carrion and Waterbird Surveys. We conducted peri-
odic surveys on rivers and reservoirs to assess temporal
availability of carrion. We sampled representative stretch-
es of reservoir shoreline where we expected carrion to
accumulate, e.g., coves, bends, and especially where riv-
ers entered reservoirs. We slowly followed shorelines by
boat, identifying and measuring all carrion fish, birds,
and mammals encountered. We noted factors contribut-
ing to death, e.g., trauma, evidence of spawning, fishing
paraphernalia. On rivers, we selected one to three 100-
m areas in each territory where carrion was likely to ac-
cumulate, and with particular attention to channelbends. We surveyed for waterbirds from one or two
points offering wide views per territory, or by makingcounts while traveling along water bodies (e.g., during
carrion surveys), noting the species and numbers pres-
ent.
Results
Diet. We identified 19 species of fish, 26 birds,
16 mammals, and three reptiles from (1) the re-
mains of 2601 prey individuals collected from
nests, under perches, and after foraging events at
23 breeding territories, and (2) observations of
713 prey items delivered to nests (Table 1). Meanbiomass percentages for each class in remains from
all sites were 75.5% fish, 14.3% mammals, and
10.2% birds. Four groups accounted for nearly all
fish biomass: catfish (mainly channel catfish), suck-
er (desert and Sonora suckers), carp, and perci-
forms (mainly largemouth bass, black crappie, and
yellow bass). Seven taxa exceeded 15% of fish bio-
mass at one or more of 23 territories sampled in
central Arizona: sucker at 12 territories, carp at 12,
channel catfish at 10, largemouth bass at six, flat-
head catfish at three, crappie at two, and yellow
bass at two.
Comparisons of prey remains with prey deliver-
ies over similar time frames consistently showed
that biomass estimates from remains overrepre-
sented mammals and birds over fish, and catfish
over suckers and perciforms (Hunt et al. 1992). In
three territories where items and deliveries were
within comparable time frames, 7 of 56 fish
(10.3%) identified in remains were suckers, where-
as 124 of 342 (33.2%) fish deliveries were suckers
(X^ = 13.1, df — 1,7* = 0.0003). Remains versus
delivery ratios for catfish in these samples were 24:
56 (42.8%) and 56:342 (16.4%) (x^ = 47.6, df =
1, P < 0.0001). An experiment involving a blind
sample of 45 fish fed to a captive eagle supported
our field data in that soft-boned fishes tended to
be underrepresented, e.g., 100% of carp appeared
in the remains, 80% of catfish, 60% of the some-
what softer-boned suckers, and only 8% of trout (T.
Gatz and M. Jakle, unpubl. data).
As expected, suckers were the most commonprey for pairs nesting on cool, free-flowing reaches
nearest the headwaters or at sites offering access
to regulated river reaches downstream of hypolim-
250 Hunt et al. VoL. 36, No. 4
Table 1. Prey biomass estimates from prey remains and observed prey deliveries (in italics) for fl Bald Eagle
territories on the Salt and Verde rivers where sample sizes exceeded 40 items. Letters in parentheses refer to damreleases from the cool hypolimnion (C) or the warm epilimnion (W).
Percent Biomass
Breeding
Area Setting N Suckers Carp Catfish
Perci-
forms
Mam-mals Birds Other
Ladders Free-flowing river 79 8 48 20 1 18 5 0
deliveries 130 45 33 17 0 3 0 2
East Verde 95 5 47 27 2 12 5 2
deliveries 103 14 49 17 8 6 0 6
Redmond 156 5 18 55 1 12 4 5
Final Free-flowing river 107 5 19 47 13 8 8 0
deliveries and reservoir 46 0 10 55 27 0 3 5
Horseshoe 95 1 8 36 31 4 19 1
deliveries 48 0 34 11 40 2 0 13
Blue Point Regulated river (C) 85 10 7 21 22 18 22 0
deliveries and reservoir 152 28 2 9 41 8 8 4
Bartlett 47 55 11 18 7 9 0 0
deliveries 234 66 2 9 15 6 0 2
Orme Regulated river 56 45 4 3 2 34 12 0
Et. McDowell 62 66 5 5 1 18 5 0
Chff Regulated river (W)
and reservoir
45 0 46 18 27 5 4 0
“76” Creek 59 5 38 2 1 41 13 0
netic dam releases (Table 1). Perciforms were tak-
en mainly in the reservoirs. Eagles obtained carp
primarily in warm, free-flowing reaches upstream
of reservoirs and in a river fed by epilimnetic re-
leases (Table 1). Catfish (channel and flathead)
were widely utilized, the highest numbers taken
from free-flowing river reaches and in a reservoir
(Alamo) with only seasonal inflow (Haywood andOhmart 1986).
Estimates of mammal biomass from remains ex-
ceeded 25% at six breeding territories. Most fre-
quently identified were black-tailed jackrabbit {Le-
pus californicus) and cottontail rabbit (Sylvilagus
audubonii). We recorded only 32 mammals among713 prey items observed delivered to nests (4.5%
of items) despite a more substantial representation
m prey remains from those nests (18.3%). We at-
tribute this disparity to the greater use of mammalsearly in the breeding season and to biases associ-
ated with bone persistence.
Waterbirds were more important to Bald Eagles
in early winter than during the nesting season, par-
ticularly at territories containing reservoirs. In win-
ter, the percentages of birds observed taken (as
compared with fish) were 50% in December, 56%in January, and 13% in February, as compared with
5% in March, 1% in April, and 0% in May. The most
commonly recorded birds taken among 30 identi-
fied were American Coots {Fulica americana, N— 15)
and Eared Grebes {Podiceps nigricollis, N = 8).
Conditions of Prey Acquisition. Eagles took
some fish species only in riverine conditions, oth-
ers only from reservoirs, and some from both. Ofthe seven important fish taxa recorded during prey
delivery observation, numerical ratios of their ori-
gin in rivers versus reservoirs at four territories
containing both environments were as follows (riv-
er : reservoir):yellow bass (0:31), crappie spp. (0;
40), largemouth bass (2:22), flathead catfish (3:5),
channel catfish (4:17), sucker spp. (105:0), and
carp (3:30). In reservoirs, eagles obtained most fish
as carrion (or moribund), i.e., 66% of 125 fish of
known status (excluding piracies) were obtained
from reservoirs as carrion, whereas 12% of 201 fish
from rivers were carrion.
Suckers. At least 83% {N = 114) of suckers were
alive when taken, 5% were pirated, 3% were car-
rion, and 9% were of unknown status. Bald Eagles
December 2002 Bald Eagle Foraging Ecology 251
caught them mainly in riffles while they spawned
or foraged. Of 64 depth measurements at strike
points for live suckers, 80% were in water <30 cmin depth; mean depth at strike points of these 51
shallow water captures was 16.4 cm (SD ± 7.3).
Carp. Eagles obtained carp from both rivers and
reservoirs. In rivers, eagles caught them in the shal-
lows of runs and riffles, 17 of 20 strikes in water
less than 36 cm deep. We were unable to deter-
mine under what conditions carp were captured in
reservoirs.
Catfish. We estimate from prey collections that
channel catfish contributed almost three times the
biomass as flathead catfish (301 182 g versus 92 304
g, respectively). Excluding piracies, we observed
nesting Bald Eagles taking channel catfish on 51
occasions: 75% on reservoirs and 25% on rivers.
On reservoirs, 81% of 26 catfish of known status
were obtained as carrion, whereas on rivers, 27%of 11 were carrion. Although the sample of con-
ditions at strike points for live channel catfish in
rivers was small, it differed from those noted for
other species. Eagles captured five in pocket water,
three in runs, and none from riffles. The mean of
six depth measurements was 58 cm (SD ± 28.1).
We occasionally observed catfish swimming near
the surface in riverine pools (Van Daele and Van
Daele 1982), and “blooms” of carrion channel cat-
fish (ca. 20 cm long) appeared in late spring at two
reservoirs (Horseshoe and Roosevelt)
.
Perciforms. At four breeding territories contain-
ing reservoirs (Bartlett, Saguaro, Horseshoe, and
Roosevelt), we recorded delivery of 61 largemouth
bass, 51 black crappie, 41 yellow bass, and 14 oth-
ers (mainly sunfish). Eagles obtained these perci-
forms mainly as carrion from the reservoir or as
they lay moribund at the surface. Of 76 dead or
moribund perciforms found in carrion surveys onthese same reservoirs, 29 were yellow bass, 15 large-
mouth bass, 13 black crappie, eight bluegills, four
smallmouth bass, four green sunfish, and three
walleye. The yellow bass and black crappie were
apparent victims of spawning stress, whereas manyof the largemouth fatalities were angler-related.
Birds and Mammals. Coots were attacked whenthey foraged in the grassy shallows of reservoirs.
Eagles caught grebes and waterfowl either by
stooping repeatedly at groups in open water or by
approaching low (<1 m) over the surface, snatch-
ing the prey in passing. We observed no attempts
at live mammals.
Habitat Use. We observed eagles foraging in rif-
fles disproportionate to their occurrence along ihe
river. At Ladders, 54% of 58 prey captures were in
riffles, the latter composing only 5% of riverine
habitat within the 22-km foraging range of the ea-
gles. At East Verde, 46% of 61 observed foraging
events were in riffles, compared to 15% availability
within 19 river km. Along 2-3 kilometers of river at
Bartlett, 73% of 119 observed foraging attempts
were in riffles compared with 8% availability. At
Blue Point, 32% of 28 attempts were in riffles com-
pared with 4% availability. The frequency of riffle
use in part reflected the high proportion of sucker
captures in those territories. As noted, eagles cap-
tured suckers mainly in riffles, carp most often in
runs, and channel catfish in pocket water and runs.
In 162 measurements of turbidity at strike points
for live fish, 136 (84%) were in water that was
“clear to the bottom.” When rivers became turbid
during prolonged periods of snowmelt, eagles
tended to forage elsewhere, such as in clear trib-
utaries.
At the four breeding areas containing both riv-
erine and reservoir environments, eagles mostly
foraged from reservoirs (>50% of locations). At
two territories where eagles nested on the river 3.6
km and 7.0 km from reservoirs, 51% and 61% of
total relocations were on the reservoirs, respective-
ly. For a radio-tagged pair whose nest was situated
where a river entered a reservoir, 85% and 86% of
relocations were on the reservoir. At a territory
where the nest was about 2 km from both river and
reservoir, 59% of relocations were on the reservoir.
Among a biomass total of 113.5 kg of delivered
prey items recorded at these four territories,
28.4%, 65.9%, 93.9%, and 48.4% were obtained
from the reservoir. Of 641 forage attempts record-
ed at these territories, 386 (60%) were on reser-
voirs.
Foraging Range. Free-flowing river. We comparedeagle foraging ranges at two territories (Ladders
and East Verde) situated on the free-flowing Verde
River far upstream of the dams and reservoirs (Fig.
1). The nests of both pairs were on cliffs overlook-
ing the river: the two nests at Ladders were directly
over bar-riffles, but the East Verde nest was about
1 km from the nearest bar-riffle. At both territo-
ries, the null hypothesis of random selection by the
eagles of 1-km segments containing bar-riffles was
rejected (Chi-square tests, P < 0.005). At East
Verde, 72% of mainstem relocation points were
within seven 1-km segments, in the aggregate con-
taining 100% of the bar-riffles within the 19 km
252 Hunt et ajl. VoL. 36, No. 4
*34 37« ^36 137 153 1' UO U’
(0 14
|„UJ2 10«
S 8oc 6d)
g 40.
Fast Verde Male
494 relocations
124 125 ‘>7 Ti ' -
Bar Rime
-
I
V'erde River ^ 'tritaiHries'
''Q"_ tribSy Vei4e River
Figure 2. Foraging range of the radio-tagged breeding male Bald Eagle at the East Verde territory. Relocation
percentages in the nest vicinity were adjusted according to the proportion of observed prey deliveries from those 1-
km segments (see Methods) . Open bars quantify cases in which trackers could not precisely locate the eagles; dotted
lines extending laterally from open bars indicate zones of eagle occupancy for the imprecise locations (tributary
relocation percentages not shown).
foraging range (123-141 km), but containing only
21% of the available channel-riffle habitat (Fig. 2).
At Ladders, 54% of visits within the 22 km range
were within the six 1-km segments containing bar-
riffles.
There were clear, seasonal shifts in prey and hab-
itat use (Fig. 3). For example, in March, when the
Verde River was turbid, 17 of 18 prey items record-
ed at the East Verde territory were mammals. In
April, the East Verde male traveled up two relative-
ly clear tributaries to forage on spawning suckers.
By early May, he was foraging almost exclusively in
the mainstem Verde River, taking carp and catfish.
His use of river sections downstream of the nest
peaked during the mid-point of the brood cycle,
then shifted dramatically to the area upstream of
the nest containing a large bar-riffle.
Regulated river and reservoir. The home ranges of
the Bartlett and Blue Point pairs (29 and 26 river-
km, respectively) both contained a deep-release
(cool) regulated river section below a reservoir fed
by a regulated reach. At both breeding territories,
90
(AC
80
70
8 60
O<D 500^
O 40•4—
•
5 30UO 200-
10
Downstream from Nest
Upstream from Nest
H Tributaries
P1-9 April
Af =49
ali
14-23 April
N =60
28 April - 7 May
N = 109
13-21 May 26 May - June 4
A/ = 137 A/ = 121
Figure 3. Chronological shifts in ranging by the radio-tagged male at the East Verde territory to areas outside the
nest vicinity.
December 2002 Bald Eagle Foraging Ecology 253
most river visits by radio-tagged eagles were in the
vicinity of the first large cliff downstream of the
respective dams. Suckers were abundant in riverine
environments at both territories. At Bartlett, a
large bar-riffle was present near the nest cliff. This
1-km segment and the only two others containing
bar-riffles received the three highest relocation
scores (51%, 8%, and 8% of 164 river relocations
of the male) within a home range containing 13
km of river. At Blue Point, the 1-km segment with
the highest river relocation score (56% of 314 river
relocations of the male in two breeding seasons)
contained a large cliff above a bar-riffle. At both
territories, the eagles traveled downstream as far as
9 km to forage on suckers in early spring, but as
the zones of suitable sucker spawning tempera-
tures moved upstream, the birds responded ac-
cordingly. At Bartlett, this phenomenon is appar-
ent when one divides the 1989 nesting season (26
February-20 May) into three equal periods. In the
early period, 35% of relocations by the breeding
male were to the area within about 2 km of the
nest (3.6 km downstream of the dam), but these
rose to 59% and 86% in the middle and late pe-
riods. Relocations to the area 3-10 km downstream
of the nest declined from 65% to 36% to 14% dur-
ing the three periods. In 20 comparisons of river
temperatures between the nest vicinity and a lo-
cation about 5 km downstream, the downstream
temperatures were invariably higher (paired t-test,
t = 11.3, P < 0.0001). During the early period
when the eagle traveled downstream so frequently,
the mean stream temperature was 13.5°C at the
nest vicinity and 15.5°C at the downstream loca-
tion. Importantly, Sonora suckers spawn at 14-
18°C. Sucker spawning peaked in the downstream
reach in mid-March and ceased by mid-April, whenspawning in the upstream section reached its peak.
Both the Bartlett and Blue Point eagles frequent-
ly perched and foraged in reservoir environments:
51% of 334 relocation points by the Bartlett male
were on the reservoir, and 59% {N — 765) for Blue
Point. Waterbirds (mainly American Coots and
Eared Grebes) attracted eagles at both territories
to the reservoir in winter. In spring, the main in-
ducement for reservoir use in both areas was the
presence of carrion (or moribund) fish, mainly yel-
low bass (Saguaro), black crappie (Bartlett), and
largemouth bass (both reservoirs).
Free-flowing river and reservoir. The Horseshoe and
Pinal breeding territories both contained a free-
flowing river section that entered a reservoir. The
Horseshoe nest was at the upstream end of a res-
ervoir, and the Pinal nest was 7 airline km up-
stream of a reservoir. All four radio-tagged adults
foraged primarily at the reservoir inflow. Even
though the Horseshoe nest was at the inflow, the
use of the river was relatively low (male = 15%,female = 18%). Resources offered by these reser-
voirs included wintering waterbirds and carrion
fish. As in the other four territories, the radio-
tagged birds at Horseshoe and Pinal changed their
patterns of home range use during the course of
the nesting season. In winter, the Horseshoe andPinal adults traveled downstream to the body of
the reservoir where waterbirds were concentrated.
By March they began foraging closer to the nest,
and both pairs traveled further to forage during
the late stages of the nesting season. Home range
sizes for the Horseshoe and Pinal pairs were 17 and
27 river-km, respectively.
Environmental Setting and Nesting Success. Wecompared reproductive performance for the peri-
od 1980-90 among breeding territories (produc-
tive at least once during that period) in modified
versus unmodified environments. Productivity
(mean young fledged ±SE/nest year) of pairs mareas altered by dam construction (1.07 ± 0.11, N— 12 territories, 89 nest-years) was almost identical
to that of pairs in areas not altered by dams (1.04
± 0.10, N = 9 territories, 71 nest-years) (t — 0.08,
P = 0.94).
Discussion
Bald Eagle pairs foraged on a wide variety of
prey, the distribution within each diet was rarely
skewed toward a single taxon. If anything, we un-
derestimated the degree of dietary diversity by
lumping some taxonomic groups, by underrepre-
senting the pre-egg-laying diet when birds and
mammals made important contributions to fat stor-
age, and by not including the 4-9-wk post-fledging
period when dependent young remained in their
natal territories. Our results were consistent with
those of Grubb (1995) who hypothesized that
mammals may help to fill a dietary gap during pe-
riods of high turbidity (e.g., snowmelt) when fish
are less visible.
Underlying the diverse and variable diet of nest-
ing eagles were the ordering of gross habitat fea-
tures within the landscape (e.g., reservoirs, rivers,
tributaries), the variety of aquatic habitats within
them (e.g., riffles, runs, pools, reservoir inflows),
the changing factors that influenced the timing of
254 Hunt et at. VoL. 36, No. 4
prey availability (e.g., flow, temperature, and tur-
bidity),and the diverse natural history of each prey
species (e.g., spawning cycles, foraging behavior).
Our radio-tracking data and observations of prey
deliveries at the intensively studied territories sug-
gested that prey sources for nesting eagles rarely
remained constant throughout the reproductive
cycle.
Our findings support that prey and habitat di-
versity are important to many Bald Eagle pairs in
Arizona, allowing for continuous food availability
through a lengthy breeding season. Thus, it would
seem that dams may benefit Bald Eagles to the ex-
tent of creating water temperature discontinuities
and additional aquatic habitats, some with large
populations of fish. However, environments modi-
fied by dams were not necessarily better for Bald
Eagles than those on free-flowing river reaches,
given that reproduction in the two settings was
nearly identical. Eagles do appear to benefit from
the presence of exotic fish which form major com-
ponents of the eagles’ diet in both regulated and
unregulated environments.
Even so, current conditions are not necessarily
more supportive of Bald Eagles than were those in
the pristine (pre-livestock) landscape when morerobust, infiltrated soils likely slowed the transport
of water to rivers which thereby maintained moreconsistent flows over the yearly cycle of rainfall
(Olmstead 1919, Hastings 1959, Hastings andTurner 1965, Hayden 1965). Moreover, somestream courses, now seasonally dry, were perennial
in past centuries and doubtless supported fish pop-
ulations. Since the 1980s, at least nine pairs of Bald
Eagles have fledged young on free-flowing reaches
and tributaries that are probably now more turbid
than they would have been before the grazing era.
Today, Bald Eagles nesting upstream of reser-
voirs feed primarily on four fish species: Sonora
suckers, desert suckers, carp, and channel catfish.
Of these, only the suckers are native to Arizona.
However, five other species of hsh of appropriate
size categories were once present: Colorado pike-
minnow {Ptychocheilus lucius)
,
razorback sucker {Xy-
rauchen texanus), flannelmouth sucker { Caloslomus
latipinnis), roundtail chub (still fairly common),and bonytail chub {Gila elegans) (Minckley 1973).
Several reports attest to the early abundance of na-
tive fishes (Rostlund 1952, Minckley and Alger
1968, Haase 1972). Native Americans used themextensively for food, as did the settlers that cameto the region in the mid-1800s (Davis 1982). Even
as late as the early 1900s, fish were so common in
the lower Salt and Gila rivers that they were sold
as feed for domestic animals and as fertilizer
(Minckley 1973). Now, the Colorado pikeminnow,
the razorback sucker, and the bonytail chub are
federally listed as endangered.
Although we cannot be certain if the commu-nities of native fishes occurring in the pristine riv-
ers supported nesting eagles, it is quite possible
that the four species of suckers, augmented by wa-
terfowl and spawning runs of pikeminnow and pos-
sibly others, formed a complete prey base. Because
suckers feed and spawn in shallow water, they are
ideal prey for eagles. Our study suggests that eagles
would have benehted if the native fishes were to
have spawned at different times. Such would be
expected, considering that any coevolved commu-nity of fishes would tend toward spawning differ-
entials in time and space (some ascending tribu-
taries) because of niche similarity and competition
among fry.
ACKNOWI.EDGMENTS
The U.S. Bureau of Reclamation (USBR) funded this
work. We acknowledge the cooperation of the Arizona
Game and Fish Department (AGFD), U.S. Fish and Wild-
life Service (USFWS), Arizona Bald Eagle Nest WatchProgram, Salt River Project (SRP), U.S. Forest Service
(USFS), Bureau of Land Management (BUM), Bureau of
Indian Affairs, and the San Carlos Apache, White Moun-tain Apache, Fort McDowell, and Salt River Pima-Mari-
copa tribes. We are grateful to D. Busch, T. Gatz, M. Jakle,
and FI. Messing (USBR) who provided direction and as-
sistance throughout the project. We also thank R. Glinski,
T. Tibbitts, J. Janish (AGFD), R. Hall (BLM), D. Reigle
(SRP), and A. Harmata for help and guidance. Special
thanks are extended to R. Mesta (USFWS) for help with
data collection. G. Harris, J. Rassi, M. Greenburg, and D.
Blakely (SRP) negotiated SRP helicopter assistance for
nest climbs. D. Stewart, T. Noble, M. Ross, R. Kvale, D.
Pollock, and D. MacPhee (USFS) provided logistical sup-
port. For radio-tracking, observation, and fisheries work,
we thank BioSystems Analysis, Inc. employees G. Ahl-
born, G. Beatty, P. Becker, V. Behn, B. Bock, P. Carroll,
M. Cashman, D. CIcndenon, M. Cross, J. Driscoll, F. Fioc-
chi, A. Gertstell, J. Gilardi, F. Hein, C. Himmelwright, A.
Klatzker, P. fang, F. Lapsansky, M. Larscheid, C. I.enihan,
D. Ledig,J.Linthicum, S. Marlatt, J. Meyers, D. Monda,
N. Nahstoll, C. Page, R. Spaulding, D. Stahlecker, K.
Thompson, L. Thompson, R. Thorstrorn, D. VonGonten,
and K. VonKugelgen. For help with identification of prey
remains, we thank R. Cole, R. Miller, G. Smith, Y Petry-
szyn, P. Krausman, and C. Schwalbe. We thank P. Law for
help with statistics and J. linthicum, T. Hunt, A. Har-
mata, R. Steidl, and T. Grubb for comments on the man-uscript.
December 2002 Bald Eagle Foraging Ecology 255
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© 2002 The Raptor Research Foundation, Inc.
VERNAL MIGRATION OF BALD EAGLES FROM A SOUTHERNCOLORADO WINTERING AREA
Alan R. Harmata^Fish & Wildlife Program, Department ofEcology, Montana State University, Bozeman, MT 59717 US.A.
Abstract.—^Adult Bald Eagles {Haliaeetus leucocephalus) {N =15) wintering in the San Luis Valley (SLV),
Colorado were radio-tagged with conventional tail-mounted transmitters between 1 January-18 March
1980 and 1981 to determine migration patterns and breeding areas. Migrating eagles were followed
primarily in a single vehicle with two trackers. In 1980, radio-tagged eagles (N = 4) left the wintering
grounds within a 15-d span in March but departures in 1981 (N = 7) ranged from mid-February to
early April. Eagles initiated migration on days with higher temperature ranges, more clouds, and higher
winds than other days during winter or spring. Subsequent travel paralleled the northward movementof the 2°C isotherm both temporally and spatially. Locations and pathways of migrating eagles were
similar in both 1980 and 1981. All four eagles located on their summer range were within 102 km of
each other in northeastern Saskatchewan and northwestern Manitoba. Mean distance from the SLVwintering area to breeding or summer areas of Bald Eagles was 2019 km. Adult Bald Eagles apparently
migrated alone in spring with mated males leaving first. Migration flights began between 1015-1045 HMST and ended between 1715-1745 H. Mean daily movement was 180 km. Migration flight speeds
averaged about 50 km/hr. Altitude of flight ranged from 30-4572 m above ground level (AGL), but
most often was between 1500-3050 m.
Key Words: Bald Eagle; Haliaeetus leucocephalus; Colorado; radio-tracking, Saskatchewan; vernal migration;
wintering.
MIGRACION PRIMAVERAL DE LAS AGUILAS CALVAS DESDE UN AreA DE INVERNACION ALSUR DE COLORADO
Resumen.—Individuos adultos de aguila calva {Haliaeetus leucocephalus) {N = 15) invernando en el valle
de San Luis (VSL) Colorado, fueron provistos con radios transmisores convencionales montadc^s en la
cola, entre el 1 de enero-18 de marzo de 1980 y 1981 para determinar los patrones de migracion y las
areas de reproduccion. Las aguilas en migracion fueron seguidas en primera instancia en un vehiculo
sencillo con dos rastreadores. En 1980, las aguilas con radios {N = 4) abandonaron los campos de
invernacion en un intervalo de 15 dias en marzo, pero las partidas en 1981 {N = 7) fueron entre
mediados de febrero y principios de abril. Las aguilas iniciaron la migracion en dias con ranges de
temperaturas mas altos, mas nubes, y vientos mas altos que otros dias durante el invierno o primavera.
El subsiguiente vuelo fue paralelo al movimiento hacia el norte de la isoterma 2°C tanto temporal comoespacialmente. Las localizaciones y vias de paso de las aguilas migratorias fueron similares en 1980 y
1981. Las cuatro aguilas localizadas en su rango de verano estuvieron dentro de 102 km una de otra
en el nororiente de Saskatchewan y noroccidente de Manitoba. La distancia media desde el area de
invernacion del VSL a las areas de reproduccion o de verano de las aguilas calvas fue de 2019 km. Las
aguilas calvas adultas aparentemente migraron solas en primavera mientras que sus machos pareja sal-
ieron primero. Los vuelos de migracion comenzaron entre 1015-1045 H MST y terminaron entre 1715-
1745 H. El movimiento medio diario fue 180 km. Las velocidades de los vuelos durante la migracion
tuvieron un promedio de 50 km/h. La altitud de vuelo tuvo un rango entre 30-4572 m.s.n.m. pero la
mayoria a menudo estuvo entre 1500—3050 m.
[Traduccion de Cesar Marquez]
Relatively stable wintering populations of Bald
Eagles {Haliaeetus leucocephalus) existed in the San
Luis Valley (SLV) of southern Colorado through-
^ E-mail address: [email protected]
out the DDT era (Ryder 1965, Alamosa National
Wildlife Refuge reports 1954-83). In the 1970s, a
mean of 185 (SD = 66.6) Bald Eagles was counted
in the SLV annually (V= 5; Craig 1981). However,
origins of eagles wintering in the SLV were un-
known.
256
December 2002 Bai d Eagle Vernal Migration 257
Between December—April 1977 and 1978, win-
tering Bald Eagles (N = 36) in the SLV were
marked with yellow patagial wing markers to de-
termine their geographic origins or breeding areas
(Harmata and Stahlecker 1993). Colormarking re-
vealed fidelity of individual Bald Eagles to this win-
tering area was high, but by January 1981 only
three sightings of yellow-marked eagles occurred
outside the SLV and none were in a documentednesting area or during summer (Harmata and
Stahlecker 1993). The primary objective of the
marking program had not been realized. Clearly,
other methods were required to achieve objectives
in a timely and cost-efficient manner.
Prior to the 1980s, technology for remotely
tracking long-range movements of individual birds
(i.e., satellite platform transmitter terminals or
PTTs) was not available. However, on 28 February
1978, after being tracked locally for nearly six
weeks, an adult Bald Eagle wearing a conventional,
tail-mounted transmitter left her SLV wintering
area. She was tracked for two days over 300 kmthrough the most rugged portion of the Rocky
Mountains, being lost only due to lack of logistical
planning, not our ability to maintain contact. This
serendipitous event revealed the potential of de-
termining migration routes and breeding areas of
Bald Eagles using conventional radio-tracking. This
paper discusses results of subsequent long-range
tracking of Bald Eagles with conventional teleme-
try from one seasonal range to another prior to
widespread use of PTTs on eagles (e.g., Grubb et
al. 1994, Brodeur et al. 1996, Meyburg et al. 2001).
Objectives of this study were: (1) to determine
breeding areas of adult Bald Eagles wintering in
southern Colorado and (2) to gather information
regarding factors associated with initiation of ver-
nal migration, routes, duration, stopover habitats
used, and other factors affecting the successful
completion of migration.
Study Area and Methods
The SLV is the largest and most southern of four large
intermountain basins in Colorado. Encompassing 6475
km^, the SLV is approximately the size of the state of
Delaware. Mean elevation of the nearly-level valley floor
IS 2286 masl. High (>3050 m) mountain ranges border
the valley on east and west, merging at the northern end.
The Rio Grande and Conejos rivers flow through the SLVand numerous natural warm springs and wetlands that
seldom freeze have made the SLV attractive to waterfowl
and Bald Eagles, probably for millennia. Water develop-
ments and agriculture in the 20th century have probably
improved the attractiveness.
Between 7 January-18 March 1980 and 1981, 15 adult
Bald Eagles were captured and radio-tagged in the SLVAll were captured by a modified “Lockhart” method(Miner 1975) with and without live Bald Eagle and Gold-
en Eagle {Aquila chrysaetos) lure birds. Trap sites werechosen on the basis of frequency and duration of the
presence of two adult Bald Eagles of distinctly dissimilar
size, presumably mated, within 1.6 km. In 1981, I esti-
mated the SIV winter population at 170 Bald Eagles
(Harmata 1984).
Gender of radio-tagged eagles was assigned by methodspresented by Garcelon et al. (1985). Three were con-
firmed by behavior during copulation. All Bald Eagles
were radio-tagged with two-stage radio transmitters
mounted proximo-ventrally on the tail. Transmitter fre-
quencies were between 148.500 and 148.950 mHz. Unitlife expectancy was ^5 mo. Transmitter, antenna, andmounting tab weighed 50-57 g. Telemetry receiving
equipment included fixed channel and programmablereceivers.
Mated status of radio-tagged Bald Eagles was deter-
mined by frequency and duration of time spent in the
presence of another adult eagle of distinctly dissimilar
size, observed copulation {N = 3) in the SLV, or associ-
ation with a nest site on the breeding grounds {N = 2).
Eagles were considered unmated if diurnal movementsin the SLV were clearly independent of other eagles andthey were not observed to roost away from communalroosts with just one other eagle, as mated birds often did
Climatological data associated with days that Bald Ea-
gles left the SLV were analyzed by stepwise discriminate
analysis (Dixon 1981) to investigate meteorological con-
ditions associated with initiation of vernal migration. Cli-
matological data recorded near the geographical center
of the SLV (Alamosa, Colorado) were obtained from Na-
tional Oceanographic and Atmospheric Administration,
Asheville, North Carolina Monthly Summary Sheets. Datafor days that eagles left the SLV were compared to data
for days randomly selected between 1 January-15 April
1980 and 1981 that they did not. Variables selected for
comparisons among days were maximum, mean, andrange of temperature, percent of clear sky and meanwind speed.
Migrating eagles were followed primarily from a single
4X4 vehicle with two human trackers and a dog. Anomnidirectional antenna and two element “H” yagi re-
ceiving antenna were mounted on the roof of the chase
vehicle. The yagi was attached to a 360° traversing mount,allowing for directional tracking while the vehicle was
moving. Manpower and logistic limitations plus variability
in departure dates, routes, and travel speeds of Bald Ea-
gles prevented ground tracking of more than one eagle
at a time. One tracker drove while the other operated
the receiving equipment. Both shared navigational du-
ties. Due to often high chase speeds (up to 150 km/hr)and off-road “adventures,” visual contact with migrating
eagles could not be maintained, so migration behavior
often could not be recorded continuously, accurately, or
safely. Route, direction, and speed of the chase vehicle,
therefore, often was selected primarily to maintain max-imum audio signal strength. When contact with a mi-
grating eagle was lost, an aerial search was implementedusing local air services, A two or three element yagi an-
258 Harmata VoL. 36, No. 4
FEMALES O O O • •
MALES O o
-40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15
DAYS FROM VERNAL EQUINOX
Figure 1. Days from vernal equinox that radio-tagged Bald Eagles departed {N= 12) their San Luis Valley, Colorado,
winter ranges to initiate vernal migration, 1978 {N = 1), 1980 (N = 4), 1981 {N = 7). Open circles indicate eagles
determined to be unmated, closed circles indicate eagles that were mated (see text), and square indicates eagle of
undetermined mated status.
tenna was taped to the wing strut (high wing) or step
(low wing) of light aircraft and the area surveyed in tran-
sect style with intermittent, “lazy” circles at high altitude.
Frequencies were scanned to search for the target eagle
and other potential migrating birds. When contact was
reestablished and eagle’s status discerned as stationary,
vehicle tracking resumed. Flight altitudes were estimated
based on eagle’s position relative to the search aircraft
and trees, geography, and structures such as buildings
and radio towers while ground tracking. Eagles weremonitored in their summering grounds with Beaver air-
craft, snow machines, and snow shoes.
Results and Discussion
Initiation of Migration. Over half (58%) of ra-
dio-tagged Bald Eagles with known departure dates
(N = 12), initiated vernal migration within one
week after the vernal equinox (Fig. 1). In 1980,
radio-tagged eagles {N — 4) all left the wintering
grounds within a 15-d span in March (Table 1).
Range of known departure dates {N — 8) spanned
50 d in 1981, with the first confirmed departure of
Table 1. Residency and mated status of radio-tagged adult Bald Eagles with known departure dates from winter
ranges in the San Luis Valley (SLV), Colorado.
Eagle
Designation Sex Captured
Date
Departed SLVMatedStatus'*
MinimumResidency
in SLV(davs)
378 F 21 Jan. 1978 28 Feb. 1978 U 39
180 F 18 Jan. 1980 21 Mar. 1980 M 63
280 M 23 Jan. 1980 24 Mar. 1980'^ M 61
380 M 23 Jan. 1980 21 Mar. 1980 M 58
480 M 27 Jan. 1980 8 Mar. 1980 U 41
181 F 7 Jan. 1981 11 Feb. 1981 u 36
281 M 9 Jan. 1981 20 Feb. 1981 u 43
381 F 9 Jan. 1981 27 Mar. 1981 M 78
481 M 11 Jan. 1981 27 Mar. 1981 M 76
581 F 15 Jan. 1981 25 Mar. 1981 U 70
881 M 15 Mar. 1981 21 Mar. 1981 ?*' 7
981 F 18 Mar. 1981 1 Apr. 1981 M 15
M = mated, U = unmated (see text).
First departed on 22 March 1980, but eagle encountered a winter storm and returned to winter range.
Undetermined.
December 2002 Bald Eagle Vernal Migration 259
Table 2. Mean climatological values (±99% confidence
interval) which discriminated {P ^ 0.01) between days
radio-tagged Bald Eagles initiated northward migration
from their San Luis Valley, Colorado wintering area (De-
part) and days they did not (Remain).
Tempera-
TURE Percent WindRange Sky Speed
(°C) Clear (km/hr)
Depart {N = 11) 24 (5) 50 (26) 22 (5)
Remain {N = 21)=* 19 (4) 56 (20) 16 (5)
Randomly selected.
a radio-tagged eagle occurring in mid-February
and the last in early April (Table 1). Number of
days from the equinox that eagles departed was not
different between genders (Mann-Whitney U =
16.50, P — 0.81). However, mated eagles departed
the SLV closer to the equinox and later than un-
mated eagles (Mann-Whitney U = 3.00, P = 0.03;
Fig. 1).
Three climatological variables discriminated be-
tween days that radio-tagged Bald Eagles left the
SLV on migration and those they did not (Table
2). Eagles initiated migration on days with muchlarger range of temperatures, more clouds, and
with higher winds than other days over the winter-
spring period. Migration tended to be initiated
about 5 hr after sunrise regardless of the immedi-
ate meteorological condition.
Photoperiodism is considered to be the ultimate
stimulus for the onset of migration in birds (King
and Earner 1963). All radio-tagged Bald Eagles de-
termined to be mated left the SLV within 12 days
of the vernal equinox, indicating breeding adults
may be sensitive to equal periods of light and dark.
Unmated, nonbreeding, or immature eagles maybe equally sensitive but may not be driven by pres-
sure to procreate. In fact, first observations of sub-
adult eagles in northern ranges both years were
not until at least two weeks subsequent to the ar-
rival of the first radio-tagged adults. Migrational
movement also paralleled the northward move-
ment of the 2°C isotherm (Lincoln 1979) both
temporally and spatially, hinting that thermal cues
may also be involved in the initiation of migration.
Once the urge is kindled, proximate affectors of
Bald Eagle migration appear to be coincident with
incoming low pressure systems, associated wide
range of temperatures, cyclonic air flows, and
southerly winds; similar to conditions noted by
Bagg et al. (1950) for other birds.
Although Bald Eagles are apparently sensitive to
local conditions when migration is initiated, they
appear to be cognizant of little beyond their im-
mediate environs. Eagle 280 departed the SLV on
22 March 1980 and traveled 145 km north before
being stopped by severe snow squalls. He spent the
night on a mountain pass and as the storm per-
sisted to the north the next day, he returned to his
winter range in the valley. He spent the remainder
of that day and part of the next in close association
with a female (distinctly larger eagle) and was ob-
served to copulate during this period. He initiated
migration again on 24 March, leaving the SLV for
the season.
Migration Routes, Destination, and Navigation.
In 1980, a relatively narrow migration corridor
through Colorado, Wyoming, and Montana was
used by three radio-tagged eagles (Fig. 2). Eagle
380 became sedentary in north-central Saskatche-
wan after 15 d of migration, six of which were
spent sitting out bad weather. After four days of
almost continual solitary soaring, he was found
perched close to a larger eagle where he remained
for several hours. The next day the pair began con-
struction of a new nest on Chachukew Lake, north
of Pelican Narrows, Saskatchewan. They eventually
fledged one young in August 1980.
In 1981, eagle 281 left the SLV on 20 February,
and was followed for two days over 302 km through
the mountains of western Colorado (Fig. 3) . Direc-
tion was primarily northwest and 281 was the only
eagle tracked that crossed the Continental Divide.
Subsequent tracking of 281 was interrupted be-
cause a radio of the same frequency and pulse rate
as 281 was tracked for a day before I discovered it
was a transmitter on a collar of a bighorn sheep
( Ovis canadensis)
.
Eagle 981 left the SLV on 1 April and was fol-
lowed to about 65 km north of Casper, Wyoming,where she was lost in a snow storm because roads
became impassable. Eagle 481 was detected ap-
proaching Fort Peck Reservoir in east-central Mon-tana on 5 April. After leaving Fort Peck Reservoir,
481 flew due north about 35 km then gradually
shifted to a northwest course. This route took himdirectly to the Missouri Coteau, a ridge line run-
ning longitudinally for over 150 km in southwest-
ern Saskatchewan. He continued north along the
Coteau for about 100 km. Approaching the Cana-
dian Shield, 481 made a sudden change in course
260 Harmata VoL. 36, No. 4
Figure 2. Partial migration routes of radio-tagged adult
Bald Eagles from winter ranges in the San Luis Valley,
Colorado in 1978 and 1980. Numbers indicate eagle des-
ignation and year (Table 1). Summering area of eagle
380 is indicated by 0 (confirmed nest location).
from north to northeast, paralleling the direction
of many elongated lakes and rivers in the Canadian
Shield country. Eagle 481 was subsequently fol-
lowed to Reindeer Lake, Saskatchewan, arriving on
10 April. On 22 April, 481 was found by air asso-
ciated with a nest site on Ramuchawie Lake in west-
ern Manitoba near the Saskatchewan border (Fig.
3).
Aerial surveys covering ca. 210000 km^ of north-
ern Saskatchewan were conducted to detect signals
of other SLV Bald Eagles in mid- to late April in
both 1980 and 1981. During aerial surveys, eagle
181 was located on the Pagato River, south of Rein-
deer Lake, Saskatchewan, and eagle 581 was de-
tected briefly in the area of Trade Lake, south of
the Churchill River (Fig. 3). The signal was weak
and intermittent, which indicated either a radio
Figure 3. Partial migration routes of radio-tagged adult
Bald Eagles from winter ranges in the San Luis Valley
(SLV), Colorado in 1981. Numbers indicate eagle desig-
nation (Table 1). Summering areas are indicated by 0(nest locations). Respective 1981 and 1982 recovery lo-
cations of Bald Eagles banded in the SLV (January 1977)
are indicated by (x). Tbe October 1981 recovery location
of a Bald Eagle radio-tagged in the SLV in March 1981
is indicated by 781.
malfunction, a dead eagle, or a bird in incubation
posture. Lack of contact with other SLV eagles mayhave been a function of transmitter failure (one
was known to fail in the SLV),premature shedding
of the transmitter (one transmitter was found still
attached to broken tail feathers below a perch tree
in the SLV),mortality, incomplete survey coverage,
or summering areas were located outside of north-
ern Saskatchewan. However, the fact that 31% of
potentially-detectable eagles (N= 13) were located
within an area roughly the size of Yellowstone Na-
tional Park (ca. 9300 km^) suggests that most adult
Bald Eagles wintering in the SLV originated from
this area of Canada.
December 2002 Bald Eagle Vernal Migration 261
Mean distance (as the eagle flies) from the SLVwintering area to breeding or summer areas of
Bald Eagles was 2019 km {N - 4, SD = 50). All
eagles located on their summer ranges were within
102 km of each other in northeastern Saskatche-
wan or northwestern Manitoba (Figs. 2 and 3). Du-
ration of travel between winter and summer range
for SLV Bald Eagles with known departure and ar-
rival dates {N = 2) was 15 d. Although SLV Bald
Eagles traveled about Vs the distance to their sum-
mer ranges compared to one Bald Eagle tracked
by satellite from Arizona to the Northwest Terri-
tories (3032 km, Grubb et al. 1994), they complet-
ed the journey in only about 40% of the time.
However, the Arizona eagle was a subadult (3rd yr)
and presumably was not driven by the impetus to
nest, as were adult SLV eagles tracked.
Geography, celestial cues, and weather may all
play a role during migration of Bald Eagles. Prom-
inent physiographic features such as deep canyons,
rivers, and north-south oriented topography
seemed to assist in visual navigation during flight
(Griffin 1943). These features could have been im-
printed in the memory of eagles during their ini-
tial migrations and experience dictated direction
during subsequent flights (kinesis theory; Mat-
thews 1963). Imprinting of migration routes from
wintering areas, which compliment survival during
the first year, would be more adaptive than im-
printing during first southward migration.
Eagles did not migrate on days of total overcast,
a phenomenon also noted by Gerrard and Gerrard
(1982). The altitude of the cloud layer may have
an effect, but overcast layers over 90 m were not
experienced during tracking. Sun compass orien-
tation (Kramer 1952, 1957) with time compensa-
tion, commonly referred to as sun-azimuth orien-
tation (Welty 1982) may, therefore, be important
for orientation of adult Bald Eagles during migra-
tion.
True navigation (selection of a compass direc-
tion toward a known goal in unfamiliar territory;
Able 1980) may also be a component of Bald Eagle
migration. Migrating eagles appear to avoid strong
winds during migration because strong winds ap-
parently influence direction of flight. Eagles did
not move, except locally, during days when winds
in excess of 35 km/hr occurred prior to 0900 H.
East winds of 60—80 km/hr began about two hours
after initiation of eagle 380’s flight on one migra-
tion day and his flight path deviated well west of
direct line to the eventual goal. Flight direction for
the remainder of migration clearly compensated
for the one day blown off course (Fig. 2). Unless
tbe eagle had been exposed to the area on previ-
ous migrations, true navigation is indicated. How-ever, it is not unreasonable to assume that an adult
eagle over five years old, may indeed be familiar
with a great portion of western North America as
a result of vagaries of previous migrations. Regard-
less, redundancy in navigational systems has been
illustrated for homing pigeons (Columba livia)
(Able 1980) and in all probability, several backup
navigational systems are available to Bald Eagles,
especially experienced adults.
Migration Behavior. Mated adult Bald Eagles ap-
parently migrated alone in the spring. Eagle 380
was seen roosting solitarily at all but one stopover
location (six other eagles on the Yellowstone River
near Hysham, Montana). Eagle 481 did not mi-
grate with a mate, but often moved northward with
other adult eagles. He roosted with other eagles
three times, but two sites obviously were not com-
munal or traditional because of lack of similarity
to typical Bald Eagle roost sites (Kiester and An-
thony 1983). Paired roosting was probably a result
of facilitatory behavior influenced by poor weather
and lack of daylight remaining. Subsequent obser-
vations of migration flight confirmed he movedalone. Once in the boreal forest of the Canadian
Shield country, local eagles appeared to “meet”
him in flight and escort him through their terri-
tories, but no overt agonistic encounters were ob-
served. Occasional associations with other eagles
appeared incidental for all radio-tagged eagles and
were of short duration. Solitary migration behavior
in established pairs would reduce the possibility of
both members being lost in a local catastrophe.
Daily migration flights consistently began be-
tween 1015-1045 H MST and ended between
1715-1745 H. Mean daily movement was 180 km,
but ranged from 144-435 km {N = 5) in 1980 and33-248 km (A = 5) in 1981. Speed of migration
flights recorded averaged 50 km/hr (A = 7, 22-
144 km/hr in 1980; A = 9, 20-105 km/hr in 1981)
.
Altitude of flights recorded ranged from 30-4572
m AGL, but most often was between 1500-3050 m.
Total distances, speed, and daily duration of mi-
gratory flights indicate that under optimal weather
conditions. Bald Eagles can reach their breeding
grounds within 6 d after leaving the SLV. Penny-
cuick (1975) indicated a 2000 km migration for a
bird the size of a Bald Eagle would be near maxi-
mum attainable without eating, assuming a 25%
262 Harmata VoL. 36, No. 4
mass loss. During this study, no radio-tagged eagles
were observed feeding during migration and meanmigration distance was 2020 km. Captive eagles
commonly fast more than two weeks with no ap-
parent deleterious effects (Brown and Amadon1968, pers. observ.) and wild raptors can lose up
to 30% of body mass without problems (Newton
1979). These compensatory capacities undoubted-
ly allowed adult Bald Eagles to reach their breed-
ing grounds with sufficient energy reserve for
breeding.
All radio-tagged eagles arrived in their summerrange at a time when lakes and most stretches of
rivers were still frozen. The only areas of open wa-
ter were rapids or narrows on rivers or between
lakes. Radio-tagged eagles spent most of their time
there, presumably foraging for fish. Other eagles
observed during aerial surveys were associated with
ubiquitous holes in lake ice and viscera piles of fish
left by native commercial fishing operations. For-
aging eagles were also seen on or near caribou
{Rangifer tarandus) and moose {Alces alces) carcass-
es killed by natives or wolves ( Canis lupus)
.
A few
eagles were seen with snowshoe hare {Lepus amer-
tcanus) remains.
Regional Relationships. McClelland et al. (1994)
noted that Bald Eagles radio-tagged in Glacier Na-
tional Park, Montana, in autumn wintered west of
the Continental Divide and summered in the
MacKenzie River watershed of northern Alberta,
northwest Saskatchewan, and Northwest Territo-
ries. The summer range of a Bald Eagle that win-
tered in Arizona (west of the Divide) also was in
the MacKenzie River watershed (Grubb et al.
1994). McClelland et al. (1994) suggested that win-
tering areas may be related to the watershed of
origin and Bald Eagles be managed by application
of a “Migration Flyway Concept.” Adult Bald Ea-
gles radio-tagged and banded in the SLV wintering
area (east of the Divide) were tracked to breeding
areas in Saskatchewan and Manitoba, all in the
Churchill River watershed. Jenkins et al. (1982) fol-
lowed two adult Bald Eagles radio-tagged in Wyo-
ming during winter. One trapped on the west side
of the Continental Divide was followed to the
MacKenzie River watershed, while one trapped on
the east side of the Divide was followed to the
Churchill River watershed, similar to those from
the SLV. These data suggest a “Churchill-East
Slope” Migration Flyway exists, distinct from the
“Mackenzie-Intermountain” Flyway proposed by
McClelland et al. (1994).
Stopover areas used during vernal migration of
SLV Bald Eagles were generally widely distributed.
A tree of adequate size, secure from human dis-
turbance in any type habitat, was all that seemednecessary for roosting. In late March 1982, Swen-
son (1983) counted 232 Bald Eagles along the Yel-
lowstone River between the mouth of the Bighorn
River and Miles City, Montana. A site where eagle
380 roosted is in the middle of this stretch and
within an area where the river seldom freezes, con-
tained the most highly braided portion of channel,
most heavily wooded islands, and highest Canada
goose {Branta canadensis) populations of three sec-
tions of river studied by Hinz (1974). Use of this
section of the Yellowstone River by adults may be
dictated primarily by tradition and availability of
water, because migrating adults were not known to
feed during this study.
Areas in eastern Montana may be equally im-
portant to as many or more migrating eagles as the
more highly-publicized areas, where ephemeral
concentrations of eagles occur in western Mon-tana. Leighton et al. (1979) estimated a population
of 14 000 Bald Eagles in Saskatchewan. Some ea-
gles from north-central Saskatchewan were cap-
tured in autumn at Hauser Lake (Restani et al.
2000) and Glacier National Park (McClelland et al.
1982), while others passed through eastern Mon-tana during migration (Gerrard et al. 1978, Har-
mata et al. 1985). Both Hauser Lake and Glacier
National Park Bald Eagle concentrations are nowdefunct due to a collapsed, exotic food base (ko-
kanee salmon, Oncorhynchus nerko), but eastern
Montana habitats still support large numbers of na-
tive prey (lagomorphs, ungulates, waterfowl). How-ever, lack of a concentrated food base, diffusion of
roost sites, solitary habits of migrating eagles, plus
dispersion of departure dates from winter (this
study) and summer ranges (Harmata et al. 1985),
prohibit any accurate estimate of numbers of Bald
Eagles passing through eastern Montana. Relatively
low numbers of eagles present at any particular
time at some stopover areas in eastern Montanamay belie the true importance of these areas to
migrating eagles. Turnover of individuals appeared
to be daily, over months. Therefore, western prai-
rie states may provide important migratory habitat
for a large proportion of the continental popula-
tion of Bald Eagles over long periods.
Acknowledgments
J. Stoddart initially suggested Bald Eagle research in
the SLV. Dale Stahlecker served as co-investigator during
December 2002 Bai.d EACiLE Vernai, Migration 263
preliminary marking studies. P. Harmata (then age 5)
helped track the first migrating Bald Eagle in 1978. G.
Montopoli was instrumental for successful completion of
the first year’s migration tracking. M. Lockhart provided
details of eagle capture techniques and field assistance.
S. Werner and E. Spettigue participated in winter andmigration tracking. L. Stevenson of Pelican Narrows, Sas-
katchewan, donated flight expertise and air time. Finan-
cial assistance was provided by R. Koteen; Fred Jense,
Dept, of Veteran’s Affairs; J. Lincer and W. Clark of the
National Wildlife Federation; R. Plunkett of the National
Audubon Society; D. Flath of Montana Fish, Wildlife, andParks; 1.. Jahn of the Wildlife Management Institute andAmerican Petroleum Institute; T. Ingram of Eagle Valley
Environmentalists; S. Rainey and C. Merrit of AmericanWilderness Alliance; M. Malone, Montana State Univer-
sity (MSU) Research Creativity Program; R. Eng, MSUAgricultural Experiment Station; and R. Moore, MSU Bi-
ology Department. T. Crubb, M. Ratine, M. Restani, andD. Stahlecker made helpful comments on earlier drafts
of the manuscript. “Sarge” was the dog, a great compan-ion and a loyal friend.
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J.Raptor Res. 36(4):265-279
© 2002 The Raptor Research Foundation, Inc.
DOES NORTHERN GOSHAWK BREEDING OCCUPANCYVARYWITH NEST-STAND CHARACTERISTICS ON THE OLYMPIC
PENINSULA, WASHINGTON?
Sean P. Finn^Biology Department, Boise State University, 1910 University Drive, Boise, ID 83725 US.A.
Daniel E. Varland^Rayonier, 3033 Ingram Street, Hoquiam, WA 98550 US.A.
John M. MarzluffCollege ofForest Resources, University of Washington, Box 352100, Seattle, WA 98195 US.A.
Abstract.—To determine stand-level habitat relationships of Northern Goshawks (Accipiter gentilis) onWashington’s Olympic Peninsula, we surveyed all known historically-occupied sites {N = 30) for occu-
pancy. We measured 45 forest-stand attributes at these sites and found, using stepwise logistic regression,
that goshawks were most likely to occupy historical nest sites with high overstory depth (maximumoverstory height-minimum overstory height) and low shrub cover. Forest managers can manage for
high overstory depth (>25 m) and low shrub cover (<20%) by conducting a single, moderate-level
thinning (leaving 345-445 trees/ha) in young, even-aged 30-35-yr-old stands. Overstory canopy andshrub cover conditions should improve over a 5—10 yr period following thinning. Values for some habitat
features (i.e., percent shrub cover, percent canopy closure, and total snags/ha) in our study were near or
within the range of values reported for Spotted Owls {Strix occidentalis) in young forests on the Olympic
Peninsula. Thus, forest management recommendations described herein may also benefit Spotted Owls.
Key Words: Northern Goshawk, Accipiter gentilis; logistic regression-, overstory depth, shrub cover, Washington-,
wildlife habitat relationships, silviculture, thinning, forestry.
VARIA LA OCUPACION REPRODUCTIVA DEL AZOR CON LAS CARACTERISTICAS DEL SITIO—NIDO EN LA PENINSULA OLYMPIC, WASHINGTON?
Resumen.
—
Para determinar las interrelaciones del habitat a nivel del sitio-nido para el Azor {Accipiter
gentilis) en la peninsula Olympic de Washington, estudiamos todos los sitios ocupados conocidos his-
toricamente {N = 30) . Medimos 45 atributos de los sitios en bosques y encontramos, usando regresion
logistica paso a paso, que estos azores probablemente ocuparon historicamente sitios nido con cubierta
densa (maxima altura de la cubierta-minima altura de la cubierta) y baja cobertura arbustiva. Los
administradores de bosques puedan manejar cubiertas densamente altas (^25 m) y baja cobertura
arbustiva (<20%) llevando un simple, y moderado nivel de entresaca (dejando 345—445 arboles/ha) en
plataformas jovenes, o incluso de edades entre 30-35 ahos. La cubierta del dosel y las condiciones de
la cobertura arbustiva deben mejorar en un periodo de 5-10 ahos despues de la entresaca. Los valores
para algunas caracteristicas de habitat (v.gr. Porcentaje de cobertura arbustiva, porcentaje de cerra-
miento del dosel, y total de tocones/ha) en nuestro estudio estuvieron cerca o dentro del rango de los
valores reportados para Strix occidentalis en bosques jovenes de la peninsula Olympic. De esta manera las
recomendaciones para el manejo de los bosques que se dan aqui, pueden beneficiar ademas a los buhos.
[Traduccion de Cesar Marquez]
Of critical importance to the success of an or-
ganism is its selection and use of resources. Selec-
^ Current address: USGS, Forest and Rangeland Ecosys-
tem Science Center, Snake River Field Station, 970 LuskStreet, Boise, ID 83706 U.S.A.
^ Corresponding author’s e-mail address: daniel.varland®
rayonier.com
tion among available resources may be especially
important in large mobile organisms that rapidly
move through extensive areas and sample available
resources at a relatively coarse grain (Stern 1998).
Large mobile organisms living in structurally-com-
plex habitats may be particularly responsive to
changing conditions because the various compo-
265
266 Finn et al. VoL. 36, No. 4
nents of their habitat may singly or interactively
affect their preferred breeding sites, thermal en-
vironment, prey abundance and distribution, vul-
nerability to predators, or their competitive status
(Hilden 1965, Patton 1997). The Northern Gos-
hawk {Accipiter gentilis; hereafter known as gos-
hawk) is an excellent example of such an organ-
ism. Goshawks inhabit boreal and temperate
forests within the Holarctic region (Squires and
Reynolds 1997). Because they are highly mobile,
long-lived, and can take a broad assortment of prey
(Squires and Reynolds 1997, Watson et al. 1998),
they are able to select among many different avail-
able habitats for breeding, roosting, foraging, and
other activities.
Much research has focused on goshawk habitat
use and requirements (Block et al. 1994, Squires
and Reynolds 1997), primarily in response to con-
cerns over habitat alteration (DeStefano 1998) and
potential population declines (Crocker-Bedford
1998). Goshawks are described as forest generalists
at large spatial scales, but are a species with nar-
rower habitat requirements at nest sites (Squires
and Reynolds 1997). At the nest-stand scale, re-
search has shown that goshawks select stands with
large-diameter trees and high canopy closure, re-
gardless of forest type or region (DeStefano 1998).
To evaluate relationships between extant habitat
and goshawk site-occupancy, we measured 45 forest
characteristics in nest stands at 30 historical sites
(Table 1); 29 sites were on the Olympic Peninsula
and one was just south of this location (Fig. 1).
Hereafter, because of the proximity of this site to
the peninsula, all sites are referred to as Olympic
Peninsula sites.
Our objectives were to: (1) estimate current oc-
cupancy and breeding rates at all historically oc-
cupied goshawk nest sites on the Olympic Penin-
sula, (2) describe the relationship between
goshawk nest-stand occupancy and nest habitat at-
tributes (see Finn et al. 2002 for descriptions at
larger spatial scales), and (3) offer managementrecommendations based on our findings. We hy-
pothesized that the 30 historical nest sites we iden-
tified for study would still be occupied during our
study if forest conditions at these sites had not
been degraded since they were first discovered. Wereasoned that habitat degradation at nest sites
would result in sites being unoccupied and that
sites we found to be occupied would more closely
resemble forest conditions at historical sites whenthey were used by goshawks.
SruDY Area
The peninsula is composed of a central core of ruggedmountains surrounded by more level, forested lowlands.
Elevation ranges from 0-2420 m, although all known gos-
hawk nests were restricted to elevations ranging from ca.
150-810 m. Mixed coniferous forest is the dominant veg-
etation over most of the peninsula although tree species,
age, and composition vary along a west-east moisture gra-
dient and from natural and anthropogenic disturbances
(Franklin and Dyrness 1988, Agee 1993). Western slopes
are dominated by Sitka spruce {Picea sitchensis)
,
western
hemlock ( Tsuga heterophylla) , and western redcedar(Thu-
ja plicata) whereas the central and eastern portions con-
tain pure or mixed stands of western hemlock and Doug-las-fir (Pseudotsuga menziesii)
,along with western redcedar
and Pacific silver fir {Abies amabilis). Riparian and re-
cently-disturbed areas usually contain stands of red alder
{Alnus rubra), which may also grow in the understory or
in tree gaps on older upland sites. Understory and shrub-
layer densities vary widely and contain western hemlock,
red alder, Pacific rhododendron {Rhododendron macro-
phyllum), sword fern {Polystichum munitum), and salal
( Gaullheria shallon)
.
Vegetation on the Olympic Peninsula is influenced
greatly by the management strategies of the four princi-
pal landowners, resulting in a mixture of forest stands of
varied serai stages. The Olympic National Park (ONP,365 000 ha, Holthausen et al. 1995) does not engage in
commercial timber harvest. Under the Northwest Forest
Plan, the ONP is classified as Congressionally Withdrawn(USDA and USDI 1994). The oiympic National Forest
(ONF, 254 000 ha) is managed under the Northwest For-
est Plan for multiple uses (USDA and USDI 1994) in
which forest management now occurs at low levels in lim-
ited areas. Forest management on lands managed by the
Washington Department of Natural Resources (DNR,164 000 ha) is guided to a significant extent by a Habitat
Conservation Plan (Washington State Department of
Natural Resources 1997). However, the focus on these
lands and on private forest lands (347 000 ha) is on com-mercial timber production and forest management. For-
est cover conditions on the ca. 1.2 million ha of the
Olympic Peninsula may be summarized by the percent
of total area of each ownership class in nesting, roosting
or foraging habitat for the Spotted Owl {Strix occidentalis)
as defined by Holthausen et al. 1995: ONP—46%, ONF= 38%, DNR = 20%, and private/other non-federal =
7%.
MRtJIODS
Occupancy at historical nest sites is an important mea-sure of habitat suitability because goshawks usually exhib-
it high site fidelity (Crocker-Bedford 1990, Woodbridgeand Detrich 1994, Squires and Reynolds 1997). We mea-sured stand attributes at historical nest sites and avoided
measures at random locations to eliminate the inherent
bias of most use-availability studies that statistically test
what is already known; that animals are nonrandomly dis-
tributed in the environment (Cherry 1998, Johnson1999).
Occupancy Surveys. We defined 30 goshawk location
records as historical nest sites after reviewing all sight re-
cords in state and federal databases. All historical nest
December 2002 Goshawk Nest-stand Habitat 267
Table 1. Northern Goshawk survey effort at 30 historical nest sites (170 or 314 ha) on the Olympic Peninsula,
Washington, 1996-98. In 1996, a 170 ha area was surveyed around each site and in 1997-98, a 314 ha area was
surveyed.
Site Name/Number®
1996
No. OF Visits
1997
No. OF Visits
1998
No. of Visits
Sta- Court-
TUS SHIP
Nest-
ling
Fledg-
ling
To-
tal^
Court-
ship
Nest-
ling
Fledg-
ling
To-
tal^
Court-
ship
Nest-
ling
Fledg-
ling
To-
tal’’
Calawah/Sitkum/ 1
2
O 2 2 1 5 2 2 1 5 3 1 4
Raney Creek/29 O 1 2 1 4 1 1 2 1 3 2 6
Dungeoness/16 1 1 1 1 1 3 1 1 2
Burnt Mountain/2 O 3 7 1 11 3 2 1 6 1 1 2
The Hole/30 O 1 6 1 8 3 3 1 7 1 1 2
Donkey Creek/26 O 1 6 1 8 3 2 2 7 1 2 1 4
Snow Creek/ 18 U 2 2 4 3 1 4 1 2 1 4
Morganroth Flat/20 u 1 2 1 4 1 3 1 5 2 2 4
Swede Road/4 u 1 3 1 5 3 1 4 3 1 4
Bear Creek/3 u 2 1 1 4 3 1 4 1 2 1 4
N Fork Solduc/7 o 1 1 2
Mount Zion/ 14 o 1 1 2
Wolf Creek/ 11 o 2 2 4
West Twin River/
1
u 3 1 4
Dosewallips/24 u 3 1 4
Cook Reload/28 u 3 1 4
Wildcat Mountain/5 u 3 1 4
Bear Mountain/ 13 u 2 2 4
Boulder Creek/9 u 3 1 4
Iverson/
6
u 2 2 4
Bowman Creek/ 19 o 2 2 4
Antelope Creek/15 o 2 2 4
Lillian River/ 17 o 1 1 2
Snahapish River/25 u 1 2 1 4
Big Canyon/23 u 2 2 4
Palo Alto/ 10 u 2 2 4
Bingham Creek/27 u 2 2 4
Caraco Creek/8 u 2 2 4
Dry Creek/21 u 1 1 2 4
Minnie Peterson/22 u 2 2 4
“ See Fig. 1 for location by site number.’’ Minimum of four visits required to meet protocol. Where <4 visits shown, occupancy was determined before protocol was met
In 1996, occupancy determination was made early in nesting season by Watson (Watson et al. 1998).
sites: (1) were in the Washington Heritage Database, first
located between 1976-94; (2) were occupied by at least
one goshawk when reported; and (3) contained a large
stick nest at the time of the goshawk sighting. Annualdata on goshawk occupancy were unavailable for all of
these sites, so no historical analyses were possible. Wesurveyed each historical nest site for goshawk occupancy
using standardized aural broadcast surveys (Kennedy andStahlecker 1993, Joy et al. 1994, Finn et al. 2002). Wesurveyed a minimum of a 1 70-ha circle surrounding 10
historical nest sites in 1996 and a 314-ha circle (1 kmradius) surrounding 20 historical nest sites in 1997-98.
The survey area was centered on the most recently used
nest structure or, when no nest structure was found, on
the UTM coordinates on record for that nest site. Be-
cause goshawks are highly mobile and tend to be secre-
tive, we considered a historical nest site to be occupied
if at least one goshawk was visually detected within 1 kmof a nest during >1 survey visit (Finn 2000).
The protocol survey involved 4-1 1 survey vi.sits where
calls were broadcast from each station once during nest-
ing, with 1-2 of these survey visits during the fledgling
stage (Table 1). Call stations were 300 m apart along tran-
sects that were 260 m apart. Call stations on adjacent
transects were offset by 130 m. If occupancy was deter-
mined during a survey visit, protocol surveys were dis-
continued but one additional site visit was made during
the fledgling stage to count the number of young
268 Finn et al. VoL. 36, No. 4
* JO •
^9*1« ^'2
^ Olympic23^ 24
8 *
30
14
20
,28
17
Olympic
National
Park
26^ 18
3^ ^21
A 722
Nation^29
IS
16
Pacific
Ocean
Nest Survey Years
1996 - 1998
• 1997
^ 1998
* 6
Forest
2S
19
•••*
i ‘i
0 ^3
Figure 1. Location of 30 historical goshawk nest sites (170 or 314 ha) on the Olympic Peninsula, Washington.
Goshawk sites outside Olympic National Park and Olympic National Forest were located on land managed by the
Washington Department of Natural Resources or owned by industrial timber companies. Numbers shown are histor-
ical nest site numbers; these correspond to those identified by site name in Table 1. All historical sites were first
discovered by happenstance, 1976-94. Each site was surveyed for goshawk occupancy in 1996-98, with 10 sites re-
ceiving 3 yr of surveys and 20 receiving 1 yr.
December 2002 Goshawk Nest-stand Habitat 269
fledged. With one exception, where another research
group checked on nest status (Dungeoness site in 1996;
Table 1), all known nests were checked for signs of oc-
cupancy on 2-6 occasions (dependent on nest condition)
during the nesting season.
Because goshawk occupation of historical sites can vary
over time (DeStefano et al. 1994, Keane and Morrison
1994), we surveyed 10 historical nest sites all three years.
This provided an assessment of among-year site occupan-
cy. Seventy percent of the sites maintained the same oc-
cupancy status among any pairing of years, indicating
that goshawk occupancy was consistent among years sam-
pled (Finn et al. 2002; Table 1). Therefore, we classified
all known historical nest sites on the peninsula as occu-
pied if they were occupied Sil yr (N = 12) or not-occu-
pied if they were not found occupied during any of the
three survey years {N = 18).
Classifying sites as “occupied” or “not-occupied”
based on one year of surveys leaves room for misclassifi-
cation. Sites not occupied during the year of survey mayin fact have been occupied earlier or later when no sur-
veys occurred. To address this problem we set a = 0.10
as the upper limit for significant differences between oc-
cupied and not-occupied sites to counter the possibility
that variances were higher in our not-occupied group of
stands because of misclassification. In addition, the man-agement recommendations we provide focus on the at-
tributes of occupied sites rather than on differences be-
tween occupied and not-occupied sites.
Habitat Analysis. To assess nest-stand habitat we mea-sured vegetation characteristics at 30 historical nest sites.
We defined the nest stand as the homogeneous forest
patch surrounding a goshawk nest and delineated stands
by scribing boundaries along ecotones and topographic
features surrounding the nest after examining 1:12 000orthophotographs, 1:16 000 aerial photographs, and 1:
24 000 topographic maps. Boundaries were ground-truthed in the field. Historical nest stands averaged 51,4
ha in size (range = 9-146 ha). Areas within historical
nest stands where habitat alteration occurred, after gos-
hawk occupancy and before our study, were included in
our measurements of nest-stand characteristics. Thus,
our habitat measurements reflect stand conditions at the
time of our surveys, not conditions when the historical
nest site was originally determined to be occupied by gos-
hawks.
We measured 45 forest characteristics (Appendix 1) in
9—13 0.04-ha, systematically placed, circular plots (x =
10.5 plots/stand, SE = 0.26) in each nest stand using a
modified USFS Region 6 Timber Stand Exam (USDAForest Service 1989) and methods described by Husch et
al. (1972) and Avery and Burkhart (1983). From plot
center, two concentric plots were established: a variable-
radius plot to sample trees >12.7 cm DBH (Diameter
Breast Height, poletimber and sawtimber) and a fixed-
radius plot to sample trees ^12.7 cm DBH (saplings andseedlings)
.
We estimated basal area, total stem density, and stem
and snag density in six size classes (12.8-38.1, 38.2-63.5,
63.6-88.9, 90.0-114.3, 114.4-139.7, and >139.8 cm) fromvariable radius plots (sampled using a 40 basal area factor
prism). We grouped snags into a single size class (^15.2
cm) because of the low number of snags in individual
size classes. We also recorded species, DBH, total height,
crown ratio, crown class, and level of mistletoe infection
for each tree. Quadratic mean diameter at breast height
(QDBH) was calculated as ((S DBH'^)/n)*^ We used a
clinometer to estimate tree heights. Crown ratio, crownclass, and mistletoe abundance were estimated visually
for eacb tree in the variable plot and then averaged for
the plot. A sample of 1-3 trees of each species on eachplot was cored for age and 10-yr radial growth rate. Over-
story and understory canopy characteristics (i.e., oversto-
ry canopy closure, and maximum and minimum oversto-
ry heights) were estimated by averaging four
measurements recorded while facing the cardinal direc-
tions. Overstory and understory canopy closure were e.s-
timated using a moosehorn (Robinson 1947). Overstory
and understory height and depth were the mean of four
ocular estimates of the height of live branching in the
two canopy layers. We used field data to calculate stand
density index (SDI, Reineke 1933) and stem density of
overstory (38.2-150 cm DBH) and understory (2.5-38.1
cm DBH) trees for each nest stand. All variables wereaveraged per plot, then per stand.
Seedling and sapling densities were measured on a
fixed-radius plot where all trees <12.7 cm in diameter
were tallied and grouped by 2.5-cm diameter class. Meanvalues of height, crown ratio, crown class, and mistletoe
infection were calculated for each diameter class. We es-
timated density and height of shrub and herb layers, andcoarse woody debris (CWD) characteristics on eight 1-m^
(Daubenmire 1959), nested plots. Plant association was
assigned to all vegetation plots following Henderson et
al. (1989).
Statistical Analysis. In our study, the number of pre-
dictor variables, 45, exceeded the experimental units, 30
Therefore, we first examined the relative differences be-
tween occupied and not-occupied nest sites for each var-
iable using box-and-whisker plots (Johnson 1999). Weused this approach because simultaneous univariate tests
increase the Type I error rate (Rice 1989) and because
the extensive hypothesis testing inherent in multiple uni-
variate tests is inappropriate for exploratory analyses such
as we undertook (Cherry 1998, Johnson 1999). We eval-
uated the box-and-whisker plots and identified variables
with central tendencies that varied with occupancy. Weselected a subset of variables that: (1) showed differences
in central tendency between occupied and not-occupied
sites, (2) had statistical integrity (approximate normaldistribution, low multicolinearity), (3) had biological in-
tegrity (accuracy of measurement, relevance to gos-
hawks), and (4) forest managers could effectively man-age (i.e., overstory canopy closure can be managed, but
percent slope cannot). The variables chosen were then
evaluated as predictors of goshawk historical nest site oc-
cupancy using stepwise logistic regression models (Hos-
mer and Lemeshow 1989, PROC Logistic, SAS Inst. 1998)
to explain variation in the binomial-response variable
(occupied vs. not-occupied, a < 0.10). We compared a
main-effect model to models that included selected in-
teraction terms to assess their significance.
Results
We surveyed 10 historical sites all 3 yr (1996-98)
and 20 sites during 1 yr (N = 50 annual site-sur-
270 Finn et al. VoL, 36, No. 4
Stem Density Decadence
Figure 2. Habitat characteristics of goshawk nest stands (9—146 ha) at 30 historical nest sites on the Olympic Pen-
insula, Washington. The historical sites associated with these stands were either not-occupied {N = 18, dark boxes)
or occupied {N= 12, white boxes) by goshawks, 1996-98. Boxes depict the median score and 25% and 75% quartiles.
Whiskers represent the 10th and 90th percentiles and black dots represent the 5th and 95th percentiles.
veys; Table 1 ) . We confirmed presence of goshawks
during 20 of these 50 site-surveys (40% occupancy
rate). At the 20 site-surveys where we observed gos-
hawks, we saw birds during >2 survey visits 75% {N= 15) of the time. During the other five site-sur-
veys that revealed occupancy, we observed an adult
goshawk during one visit. In all five cases, the
bird’s behavior suggested it occupied the area (i.e.,
alarm vocalization or site tenacity during the ob-
servation). We determined that 12 of the 30 his-
torical nest sites were occupied (Table 1 ) . All gos-
hawk responses were detected <300 m from a
historical nest site location.
Stand size at historical nest sites was 9-146 ha (x
= 51.4, SE = 6.4). Occupied nest stands were
smaller in size {x = 32.6 ha, SE = 5.5, range =
11.6-69.3) than not-occupied nest stands {x = 63.9
ha, SE = 10.9, range = 8.7—146.2). Historical nest
stands (N = 30) were composed of large {x = 57.3
cm DBH, SE = 2.4; x height = 40.8 m, SE = 1.0),
mature (x= 120-yr-old, SE = 12.5) Douglas-fir and
western hemlock trees, usually in association with
other conifers and occasionally with a few red al-
ders.
Compared to not-occupied nest stands, occupied
nest stands tended to have deeper canopies (oc-
cupied median overstory depth = 28.9 m, not-oc-
cupied median = 21.6 m; Fig. 2) and higher can-
opy closure (occupied median overstory canopy
closure = 77.7%, not-occupied median = 71.3%;
Fig. 2). Occupied goshawk nest stands had morelarge-diameter trees than did not-occupied nest
stands (i.e., occupied overstory stem density me-
dian = 191.9/ha, not-occupied median = 121.5/
ha; Fig. 2). Occupied nest stands generally con-
tained more timber (i.e., occupied SDI median =
2204.8, not-occupied median = 1184.2; Fig. 2) and
had less shrub cover than did not-occupied stands
(occupied median == 15.6%, not-occupied median= 36.9%; Fig. 2).
Overstory canopy closure, overstory canopydepth, overstory stem density, SDI, and percent
December 2002 Goshawk Nest-stand Habitat 271
Canopy Characteristics Misc.
E 25
3 0
W 2
S 1
K
• 15.0
T *5 12.5
r ^;
510.0
1
tj nz
7.5
5.0
12.5
• £ 0.0
Figure 2. Continued.
Unoccupied
Occupied
shrub cover met our variable selection criteria and
were tested as predictors of goshawk nest stand oc-
cupancy. Two of these, overstory canopy depth andpercent shrub cover, were useful in distinguishing
between occupied and not-occupied nest stands.
We found that the equation logit {occupancy) —
— 2.91 + 0.163 {overstory depth) — 0.063 {percent
shrub cover) significantly described (overstory
depth: Wald — 2.97, P = 0.043; percent shrub
cover: Wald — 4.13, P = 0.039) and was an ad-
equate fit (Hosmer and Lemeshow’s goodness of
fit = 4.087, df = 8, P = 0.850) to the data on
goshawk occupancy of historical stands (Fig. 3).
This model including only main effects fit the data
better than did any main effects plus interaction
models appraised with log-likelihood ratio criteri-
on.
Discussion
Our research indicates that occupancy of gos-
hawk nest stands does vary with nest-stand charac-
teristics. Our results agree with most other studies
that report overstory canopy as an important fea-
ture of goshawk habitat (Squires and Ruggiero
1996, Desimone 1997, McGrath 1997, Patla 1997).
These authors reported on the significance of over-
story canopy closure in the nest stand but we found
stand-wide overstory depth (maximum overstory
height-minimum overstory height) more valuable
in predicting goshawk nest-stand occupancy. Deep,
dense forest canopy {x = 28.7 m, 95% GI = 24.8-
32.6) may provide thermal cover (Newton 1979),
protection from rain, or cover protection from
predators (e.g.. Great Horned Owls {Bubo vir^ni-
anus\, Reynolds et al. 1982, Squires and Reynolds
1997).
On the Olympic Peninsula, occupied nest stands
typically had about 50% the shrub cover of not-
occupied nest stands (Fig. 2). The odds of goshawk
occupancy decreased by 47% for each 10% in-
crease in percent shrub cover (based on the odds
ratio from the logistic regression analysis). Fur-
thermore, productive goshawk nest stands hadabout half the shrub cover of occupied (10.6% vs.
19.0%; Table 2).
Most other goshawk habitat studies have not re-
ported shrub density (Speiser and Bosakowski
1987, Crocker-Bedford and Chaney 1988, Kennedy
272 Finn et al. VoL. 36, No. 4
Tree Girth Ground Cover
Figure 2. Continued.
Figure 3. The probability (p) of goshawks occupying a
historical nest site on the Olympic Peninsula, Washing-
ton, increases with increasing overstory depth and de-
creasing percent shrub cover at the nest stand scale (9—
146 ha).
1988, Siders and Kennedy 1996, Desimone 1997,
McGrath 1997, Penteriani and Faivre 1997) or have
reported it as non-important in contributing to
goshawk site occupancy (Hayward and Escano
1989, Squires and Ruggiero 1996, Patla 1997).
DeStefano and McCloskey (1997), however, con-
tend that the relative absence of goshawks from the
Oregon Coast Range is due to the dense understo-
ry conditions there, which, in turn, limit prey avail-
ability. Goshawks rarely forage near their nests
(Beier and Drennan 1997), so the lack of shrub
cover we found in nest stands may be unrelated to
prey availability. We did not measure shrub cover
beyond the nest stand scale, however. At landscape
scales (177-ha post-fledging area, 1886-ha homerange), goshawk nest stand occupancy was predict-
ed by a high proportion (60-75%) of late serai for-
est (>70% canopy closure of conifer species with
>10% of the canopy in trees >53 cm DBH) and
reduced landscape heterogeneity (Finn et al.
2002 ).
Our study may have bias because all nest sites
were located opportunistically instead of as a result
December 2002 Goshawk Nest-stand Habitat 273
Table 2. Nest stand (9-146 ha) habitat characteristics of occupied {N = 12) and productive {N = 8) historical nest
sites of the Northern Goshawk on the Olympic Peninsula, Washington, 1996-98.
Occupieda Productive'^
Variable‘s Mean SE 95% Cl Mean SE 95% Cl
Mean DBH (cm) 58.8 3.7 50.6-67.0 58.2 5.4 45.5-71.0
Quadratic mean DBH (cm) 64.0 4.3 54.5-73.5 63.6 6.3 48.7-78.6
Maximum DBH (cm) 134.2 14.7 102.0-166.4 139.4 21.9 87.7-191.2
Minimum DBH (cm) 17.4 1.1 15.1-19.7 18.0 1.5 14.4-21.6
Mean tree height (m) 43.0 1.7 39.2-46.8 43.1 2.2 37.8-48.3
Crown ratio (index) 5.1 0.2 4.6-5.6 5.0 0.3 4.2-5.7
Crown class (index) 3.1 0.1 3.0-3.2 3.0 0.1 2.9-3.2
Mistletoe (index) 2.5 0.6 1. 2-3.8 1.8 0.6 0.5-3.
1
Radial growth (cm) 1.7 0.3 1.2-2.3 1.9 0.3 1. 1-2.6
Mean tree age (yr) 147.4 22.8 97.2-197.6 128.9 25.4 68.7-189.0
Maximum tree age (yr) 247.6 .33.0 175.1-320.1 229.2 37.0 141.7-316.7
Mean sapling DBH (cm) 5.3 0.7 3.9-6.7 5.1 1.0 2.7-7.4
Mean sapling height (m) 5.7 0.6 4.4-7.0 5.7 0.8 3.8-7.5
Overstory canopy closure (%) 78.4 2.9 72.1-84.7 79.0 4.1 69.3-88.8
Minimum overstory height (m) 18.6 0.9 16.6-20.6 19.9 1.0 17.6-22.2
Maximum overstory height (m) 47.3 2.0 42.9-51.7 47.0 2.7 40.6-53.4
Overstory depth (m) 28.7 1.8 24.8-32.6 27.1 2.3 21.7-32.4
Understory canopy closure (%) 13.7 3.7 5.6-21.8 13.9 5.1 1.8-26.0
Min. understory height (m) 4.6 0.9 2.7-6.5 5.8 1.0 3.2-S.3
Maxi, understory height (m) 16.5 1.1 14.1-18.9 16.6 1.5 13.1-20.2
Understory depth (m) 11.9 0.9 9.9-13.9 10.9 0.7 9.1-12.6
Percent shrub cover (%) 19.0 4.2 9.7-28.3 10.6 2.5 4.8-16.4
Mean shrub height (cm) 41.9 4.7 31.7-52.1 39.9 4.2 29.9-49.9
Percent herb cover (%) 36.5 3.2 29.5-43.5 5.0 4.2 25.1-44.9
Mean herb height (cm) 3.6 0.2 3.1-4.1 3.4 0.2 3.1-3.8
CWD cover (%) 11.0 1.3 8.1-13.9 12.7 1.5 9.0-16.3
CWD height (cm) 42.1 4.8 31.6-52.6 45.0 5.6 31.9-58.2
CWD length (m) 11.0 0.9 9.0-13.0 11.5 1.3 8.3-14.6
CWD DBH (cm) 40.6 3.6 32.7-48.5 41.2 5.1 29.2-53.2
Slope (%) 40.5 5.0 29.5-51.5 42.5 5.7 28.9-56.0
Aspect (degrees) 269.9 26.3 218.4-321.3 294.5 63.5 170.1-58.9
Basal area (m^/ha) 71.4 5.9 58.5-84.3 68.5 5.7 55.0-81.9
Sapling den. (No./ha) 797.3 180.8 399.4-1195.2 831.3 259.3 218.1-1444.6
Small stem density (No./ha) 286.6 41.9 194.4-378.8 297.2 63.8 146.3-448.1
Med. stem density (No./ha) 151.0 22.5 101.6-200.4 146.4 23.4 91.2-201.7
Large stem density (No./ha) 39.1 7.7 22.2-56.0 32.5 8.1 13.3-51.8
Ex.-large stem den. (No./ha) 2.3 1.4 0.0-5.3 2.4 2.0 0.0-7.0
Understory stem den. (No./ha) 1083.9 219.8 600.0-1567.8 1128.5 320.9 369.6-1887.4
Overstory stem den. (No./ha) 192.5 21.9 144.2-240.8 181.3 22.6 127.9-234.8
Live stem density (No./ha) 485.4 47.4 381.0-589.8 488.0 67.9 327.4-648.6
Stand density index 2136.0 223.1 1644.9-2627.1 2107.1 317.6 1355.9-2858.3
Tree species richness (No.) 3.2 0.4 2.2-4.2 3.1 0.5 1.9-4.3
Percent hardwood (%) 1.9 1.2 0.0-4.4 1.2 0.6 0.0-2.7
Snag density (No./ha) 35.8 6.0 22.6-49.0 40.0 6.7 24.2-55.8
Seedling (No./ha) 2031.0 657.8 583.3-3478.7 2671.5 911.8 515.1-4827.9
‘‘12 sites: eight productive (where ^1 young fledged) and four occupied with no productivity.
Eight productive sites.
= See Appendix 1 for descriptions of habitat variables.
274 Finn et ai.. VoL. 36, No. 4
of systematic searches of the full range of goshawk
habitat (Squires and Reynolds 1997, Daw et al.
1998) . Our sample included all of the nests reliably
reported on the Olympic Peninsula over an 18-yr
period, 1976-94. Thus, though our sample is small,
it IS likely adequate to represent goshawk habitat
use by goshawks on the Olympic Peninsula. Fur-
thermore, Daw et al. (1998) compared goshawk
nest stand habitat in stands found opportunistically
with those found by systematic searches in Oregon
and found no differences in two key habitat vari-
ables, large tree density and canopy cover. Their
sample of opportunistically-located nests included
nests found by individuals searching for goshawk
nests with a preconceived notion of goshawk hab-
itat preferences (i.e., searching likely habitat).
Nests in our study, however, were found by individ-
uals whose reasons for being in the held varied
greatly (i.e., hikers, Marbled Murrelet {Brachyram-
phus marmoratus) surveyors, foresters conducting
timber cruises) and who, in nearly all cases, were
focused on activities other than hnding goshawk
nests. The Daw et al. (1998) study provides empir-
ical evidence that the method we employed for
identifying historic nest sites was adequate.
While we provide useful information on the
characteristics distinguishing between occupied
versus not-occupied nest stands, we recognize that
site occupancy is not necessarily indicative of qual-
ity habitat (Van Horne 1983, Vickery et al. 1992).
We believe our occupancy surveys are good indi-
cators of habitat quality for goshawks because, in
our study, nest-stand occupancy and reproduction
were closely correlated (Finn 2000, Finn et al.
2002) . Young successfully fledged from eight of 1
2
occupied sites. Moreover, only one of the 10 sites
we surveyed every year was consistently occupied,
but never produced fledglings.
Small-scale (e.g., nest tree, nest vicinity) habitat
influences on occupancy of goshawk nest stands
were not identihed in our study (Finn 2000). Thus,
forest managers should focus on stand scale (this
paper) and landscape scale (Finn et al. 2002) hab-
itat management for goshawks.
Management Impi.igaiions
Goshawk nest stand size in our study averaged
32.6 ha in occupied historical sites and 63.9 ha in
not-occupied historical sites, which is within the
range of 10—100 ha reported by Squires and Reyn-
olds (1997) for goshawk nest stands across North
America. We recommend that managers who seek
to address nest stand level habitat needs tailor
stand size after the ranges reported here.
Our research indicates that goshawk nest-stand
habitat may be provided on the Olympic Peninsula
by managing stands to create deep overstory can-
opies and low shrub cover (Table 2, Figs. 2 and 3).
Long et al. (1983) and Bailey (1996) report that
large crowns can be created in dominant and co-
dominant trees by thinning stands at 20-50 yr of
age. Thinning reduces crown competition, thereby
enhancing crown development and tree diameter
growth. Thinning, however, allows more light to
reach the forest floor which also promotes under-
story growth (Hayes et al. 1997, Thysell and Carey
2000). Hayes et al. (1997) indicated that thinning
to moderate densities facilitates crown develop-
ment but limits development of understory be-
cause the canopy closes rapidly.
To accelerate the development of deep overstory
canopies in young even-aged stands, we recom-
mend that a single moderate-level thinning take
place in stands 30-35 yr of age. On the Olympic
Peninsula and elsewhere in western Washington
and Oregon, moderate-level thinning would result
in retention of 345—445 trees/ha where heavy thin-
ning would result in retention of 148—247 trees/ha
(L. Raynes pers. comm.).
To promote deep overstory canopies at the onset
of stand initiation, planting a mixture of shade tol-
erant (i.e., western hemlock) and intolerant (i.e.,
Douglas-fir) tree species at 3-4 m spacing is rec-
ommended (ca. 1000 trees/ha, L. Raynes pers.
comm.). Spacing trees farther apart will reduce
crown competition and may result in excessive can-
opy depth (L. Raynes pers. comm.), therein cre-
ating inadequate flight space for goshawks. A sin-
gle, moderate-level thinning of the trees remaining
in the stand (there will be some mortality) at 30-
35-yr-old across the range of diameter classes, as
opposed to thinning a specific diameter class,
would promote deeper forest canopies as the stand
develops; this is because more growing space is
available, particularly for the larger trees (L. Ray-
nes pers. comm.).
Once thinning has occurred, overstory canopy
development and a concomitant reduction in
shrub cover would occur over a 5-10 yr period.
After this, stands would likely be suitable for gos-
hawk nesting for as long as they were retained.
Mean tree age of occupied nest stands in our study
was 147 yr (A = 12, SD = 71.3, range - 51-275).
December 2002 Goshawk Nest-stand Habitat 275
The four youngest occupied stands were 50-70-yr-
old while the four oldest were 200-275-yr-old.
We suggest that it is not stand age per se that is
important to goshawk nesting, instead it is the hab-
itat elements associated with older stands (this
study: deep overstory canopy, low shrub cover,
Squires and Reynolds 1997, DeStefano 1998: large
trees with high canopy closure). The extent to
which these features can be created in younger-
aged stands will make forest management for gos-
hawks more economically practicable. Other silvi-
cultural prescriptions may work as well as those wesuggest or may be more appropriate, depending
on site conditions. Currently, most stands on the
Olympic Peninsula are managed on a 40-50 yr ro-
tation (L. Raynes pers. comm.), due primarily to a
re-tooling of local sawmills to handle smaller-di-
ameter logs.
The importance of old forest attributes to the
Northern Spotted Owl, which also inhabits western
Washington forests and is sensitive to habitat loss,
is well known (Gutierrez et al. 1995, Horton 1996,
Irwin et al. 2000) . Goshawks, however, use a broad-
er range of forest structural stages than do North-
ern Spotted Owls (DeStefano 1998). We found gos-
hawks nesting in stands as young as 51 yr, andBosakowski et al. (1999) report on goshawks nest-
ing in 40-54-yr-old managed stands in western
Washington.
In research on Northern Spotted Owl use of
young forest habitat on the Olympic Peninsula,
Buchanan et al. (1999) report values for some hab-
itat features important to Northern Spotted Owls
(i.e., total snags/ha, percent shrub cover, percent
canopy closure, and coarse woody debris cover)
that are near or within the range of values wefound for these same features for goshawks (Table
2) . Thus, forest management as described herein
may also benefit Northern Spotted Owls.
Acknowledgments
We want to thank those from private companies andpublic agencies that offered their assistance. The Wash-ington Department of Natural Resources, Rayonier, Port
Blakely Tree Farms, Champion Pacific, and the University
of Washington provided funding and logistical support.
Additional support, equipment, and in-kind aid was pro-
vided by Weyerhaeuser, the Washington Department of
Fish and Wildlife, Olympic National Park, and OlympicNational Forest. We thank R. Meier, L. Raynes, S. Katzer,
N. Wilkins, T. McBride, J. Eskow, D. Runde, L. Hicks, S.
Horton, P. Harrison, D. Hays, S. Desimone, E. Seaman,S Lemioux, and L. Young for their helpful input. Tech-
nical and analytical advice was provided with enthusiasm
by L. Bond, M. Cowing, S. Gossett, B. Lehman, J. Munger,S. Novak, K. Steenhof, and T. Zarriello. Special thanks to
D. Yonkin for his outstanding help in the field, his ded-
ication to the project, and his spirit. Superior assistance
in the field was provided by B. Griffith, H. Tall, K. Bees-
ley, B. Davies, T. Bloxton, J. Delap, J. Swingle, J. Wagen-knecht, and L. Vandernoot. Thanks also to M. Fuller, S
Knick, J. Munger, K. Titus, C. Crocker-Bedford, R. Man-nan, and M. Restani who reviewed and greatly improvedthis manuscript.
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/. Raptor Res. 36(4):280-286
© 2002 The Raptor Research Foundation, Inc.
SUBORDINATE MALES SIRE OFESPRING IN MADAGASCAREISH-EAGLE {HALIAEETUS VOCIFEROIDES) POLYANDROUS
BREEDING GROUPS
Ruth E. Tingay*School of Geography, University of Nottingham, Nottingham, NG7 2RD ILK.
and the Peregrine Fund, 5668 Flying Hawk Lane, Boise, ID 83709 U.S.A.
Meianie Culver, Eric M. Haiuerman, and James D. FraserDepartment ofFisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061 U.S.A.
Richard T. WatsonThe Peregrine Fund, 5668 Flying Hawk Lane, Boise, ID 83709 U.S.A.
Abstract.—The island endemic Madagascar Fish-Eagle (Haliaeetus vociferoides) is one of the most en-
dangered birds of prey. Certain populations in west-central Madagascar sometimes exhibit a third, and
sometimes a fourth, adult involved in breeding activities at a nest. We applied DNA fingerprinting to
assess relatedness among 17 individuals at four nests. In all nests with young, a subordinate rather than
the dominant male sired the offspring. Within-nest relatedness comparisons showed that some dominant
males had an apparent hrst-order relationship with the female. Between-nest relatedness comparisons
showed that some adults had an apparent hrst-order relative at another nest in the study area. Findings
that subordinate males contribute to breeding, and that adults in an area may be related, may require
conservation measures such as translocation to assure the species’ survival.
Keywords: Madagascar Fish-Eagle, Haliaeetus vociferoides; DNA fingerprinting, mating system; nest helper,
polyandry.
MACHOS subordinados engendran descendencia en grupos de reproduccion po-
LIAnDRICA en AGUIIAS PESCADORAS DE MADAGASCAR {HALIAEETUS VOCIFEROIDES)
Resumen.—El aguila pescadora endemica de la isla de Madagascar {Haliaeetus vociferoides) es una de las
aves rapaces mas amenazadas de extincion. Algunas poblaciones en el occidente-centro de Madagascar
exhiben algunas veces un tercero y a veces un cuarto adulto involucrado en las actividades reproductivas
en un solo nido, Aplicamos un analisis de ADN para evaluar el parentesco entre 17 individuos de cuatro
nidos. En todos los nidos con juveniles, un macho subordinado mas que el dominante engendro la
prole. Las comparaciones de parentesco dentro de los nidos mostro que algunos machos dominantes
tenian aparentemente una relacion de primer orden con la hembra. Las comparaciones entre nidos
mostraron que algunos adultos tuvieron un pariente de primer orden en otro nido dentro del area de
estudio. El hallazgo de que los machos subordinados contribuyen a la reproduccion, y que los adultos
en un area pueden estar relacionados entre si, pueden hacer necesarias medidas de conservacion tales
como traslados para asegurar la supcrvivencia de la especie.
[Traduccion de Cesar Marquez]
The island endemic Madagascar Fish-Eagle {Hal-
laeetus vociferoides) is considered critically endan-
'' These two authors contributed equally to this manu-
script.
' Present address of corresponding author: Wildlife and
Fisheries Science, University of Arizona, Tucson, AZ85721 U.S.A.; e-mail address: [email protected]
gered (Collar et al. 1994) . With 63 known breeding
pairs, and an estimated total breeding population
of 100-120 pairs (Rabarisoa et al. 1997), it is
among the most endangered birds of prey in the
world (Langrand and Meyburg 1989, Watson et al.
1993, 1996). Madagascar Fish-Eagles exhibit an un-
usual dispersal and breeding strategy, possibly re-
stricting the species’ distribution and abundance
280
December 2002 Relaxedness of Madagascar Fish-Eagles 281
through limited dispersal or occurrence of in-
breeding. Breeding was believed to be monoga-
mous, but at 46% of known nests, a third, and
sometimes a fourth adult is involved with the
breeding activities of the primary pair (Watson et
al. 1999). Based on banding studies at several nests
(Watson et al. 1999), extra-pair birds were believed
to be progeny (possibly only male) from previous
years. Such delayed dispersal can result in forma-
tion of cooperative breeding groups, a relatively
rare breeding system among birds (Stacey and Ko-
enig 1990, Ligon 1999), especially among raptors
(Simmons 2000, and references therein). Ecologi-
cal or behavioral factors may influence evolution
of cooperative breeding strategies (Newton 1979,
Oring 1986, Faaborg and Bednarz 1990, Stacey and
Koenig 1990, Sherman 1995), and contribute to
attendance of additional adults at Madagascar Fish-
Eagle nests. Understanding dispersal and repro-
ductive strategies is critical for developing a man-
agement plan to ensure the species’ survival.
DNA markers have been applied to a variety of
questions regarding conservation of birds (Haig
and Avise 1996) . DNA fingerprinting proved useful
to assess relatedness at the nest (Westneat 1990,
Wetton et al. 1992, Haig et al. 1993, 1994a, 1994b)
and population (Triggs et al. 1992, Fleischer et al.
1994) levels, to infer species-level population ge-
netic structure (Longmire et al. 1991), and to es-
timate relatedness in captive stocks (Kirby 1990:
239). We used DNA fingerprinting to determine
paternity among Madagascar Fish-Eagle adults at-
tending a nest, and to examine the level of relat-
edness among adults within and between nests.
Methods
Samples. We studied three trios and one quartet of
fish-eagles at a site in west-central Madagascar (19°S,
44°30'E) on a daily basis during one breeding season
from 24 June-5 October 1999. The area is tropical decid-
uous dry forest containing several lakes (3.09-4.86 km^)
and supports 11 fish-eagle territories (Rabarisoa et al.
1997). Eagles were marked and are referred to by num-ber. Nest sites are referred to by location and nest num-ber (Ankerika 4, Befotaka 2, Befotaka 3, and Soamalipo
2). A dominance hierarchy was observed at each nest
based on aggressive interactions between adults. Aerial
pursuits (chasing) and physical displacements from ei-
ther the nest or from perches within 200 m of the nest
tree, often accompanied by a distinctive ‘displacement’
call, were observed throughout the breeding period andwere interpreted as signs of aggression (Tingay 2000).
Males are referred to as either dominant (a), or subor-
dinate ((3 or y). We were unable to establish the domi-
nance hierarchy at nest site Befotaka 3. Nestlings were
briefly removed from the nest at ca. 7 wk of age andbanded. Blood (0.1-0.25 ml) was taken from the brachial
vein (Tingay 2000), immediately placed in 4.5 ml of lysis
buffer (100 mM, pH 8.0, 100 rriM EDTA, 10 niM NaCil,
0.5% SDS) in a polypropylene tube, labeled, and stored
at ambient temperature.
DNA Purification. Approximately 200 |xl of blood/buffer solution was placed in 800 fxl lysis buffer for 10
min. Protein digestion was performed with 500 (xl of su-
pernatant from the first step, 500 |xl of fresh lysis buffer,
and 0.5 mg/ml proteinase K, with incubation at 37°Covernight. Extractions were performed in 1:1 phenolchloroform, and 24:1 chloroform : isoamyl alcohol. DNAwas precipitated using cold 95% ethanol and 5% samplevolume of 5M (0.082M final) ammonium acetate. DNAwas resuspended in 25 |xl deionized water and stored at
-20°C.
DNA Fingerprinting. DNA samples were digested sep-
arately with Hinfl, Rsal, and Haelll. Digests were loaded
onto 1% TBE agarose gels (20 cm X 24 cm), and sub-
jected to electrophoresis (Sambrook et al. 1989) at 32 Vfor 25 hr. Identity Sizing Standard (Lifecodes Corpora-
tion, Stamford, CT) was placed in several lanes of the gel
to provide molecular weight markers. DNA in the gel was
stained using ethidium bromide, photographed using fWluminescence, and transferred (Southern 1975) onto a
MagnaCharge 0.45 micron nylon membrane (Micron
Separations Inc., Westborough, MA).
Jeffreys et al
(1985) and Jeffreys (1987) minisatellite probe 33.15 was
hybridized using the NICE hybridization solution (Life-
codes Corporation, Stamford, CT) onto digested, im-
mobilized DNA. Both the 33.15 probe and Identity Sizing
Standard were labeled with NICE chemiluminescenceUnhybridized probe and size standard were washed fromthe membrane using Quick-Light wash solutions (Life-
codes Corporation) . The hybridized probe was illuminat-
ed with Lumi-Phos 480 (I.ifecodes Corporation) and vi-
sualized by exposure to Kodak XAR5 X-omat film.
DNA Fingerprinting Analysis. Gels were arrayed with
samples from individuals attending a nest adjacent to oneanother. If all hybridization bands observed for nestlings
could have been inherited from the primary pair, we con-
cluded that the primary pair was the parents. If, however,
a hybridization band could be accounted for only by par-
entage by a nest attendant, we concluded that an extra-
pair mating had occurred. There was only one adult fe-
male at each nest. The male that was most dominant andexhibited the greatest paternal investment (Tingay 2000)
was considered the male of the primary pair.
DNA band-sharing (Bruford et al. 1992) was calculated
as S = 2n^y/ (n^ + riy), where = the number of bandsshared by both individuals, = the total number of
bands exhibited by individual x, and = the total num-ber of bands exhibited by individual y. Band-sharing was
estimated for all combinations of individuals in this study
The range of S for known parent-offspring combinations
provided a quantitative expectation of how many bandsmust be shared before a hypothesis of familial related-
ness was supported.
Results
Parentage Assessment of Nestlings and Juve-
niles. DNA fingerprinting techniques were used to
282 Tingay et al. VoL. 36, No. 4
assess relatedness of 17 eagles at four nests. Twoenzymes {HaAll and RscH) produced clearly inter-
pretable results yielding a total of 34 bands scored,
24 of which were variable and 10 invariant (Table
1). Of the 24 variable bands, six were informative
in determining one or more possible parents for
the two nestlings at Soamalipo 2; three for the ju-
venile at Befotaka 3; and seven for the nestling at
Befotaka 2. Blood samples were available only for
adults at Ankerika 4. A nest-by-nest assessment of
parentage is presented below.
Befotaka 2. Female 121, a male 118, and P male
8 attended the nest. Nestling 47 shared three var-
iant /facIII and one variant Bsdi hybridization
bands with adult female 121,and two variant 7/fldlI
and one variant hybridization bands with pmale 8 ,
suggesting that subordinate P male 8 was
the father of the nestling 47, and not a male 118.
Befotaka 3. Female 6,potential a male 48, and
potential a male 150 attended this nest. Juvenile
128 shared one HadW band and one Rsa\ bandwith adult female 6 . Banding records show that ju-
venile 128 fledged from this nest in 1998. Although
band sharing showed it unlikely that either adult
male at the nest in 1999 (48 and 150) was the fa-
ther, it is highly probable that the adult female at
the nest is the mother {S — 0.95 is the highest
value in the study, female 6 has been recorded at
this nest site every year since 1993, and no other
female has been recorded at this nest).
Soamalipo 2. Female 103, a male 5, p male 136,
and 7 male 30 attended this nest. Nestling 68
shared one HaeWl band with adult female 103 and
two bands with 7 male 30. Nestling 00 shared
one HadW and one Rsoi band with adult female
103 and one HaeWl and three Rsai bands with 7male 30. The apparent father of both nestlings is
subordinate 7 male 30.
Relatedness Estimates of All Adults Within and
Between Nests. Among 136 pairwise comparisons,
band-sharing among individuals ranged from 0.58-
0.95, with a mean value of 0.79. Partitioning pair-
wise band-sharing into within- and between-nest
components showed no difference (mean S — 0.80
within nests and 0.79 between nests). After ac-
counting for eight known first-order relative pairs
(parent-offspring, full-sibling), band-sharing was
higher among first-order relatives (v = 0.87, range
= 0.82-0.95) than overall (x = 0.79; Table 2). Us-
ing these findings, relatedness among adults at-
tending nests (male-male, male-female) was deter-
mined (Table 2).
Ankerika 4. Band-sharing values suggested a po-
tential first-order relationship between female 113
and a male 31, but not between the female 113
and P male 34. Band-sharing suggested that the
males were unrelated.
Befotaka 2. Band-sharing values did not support
a first-order relationship between the female and
either male, nor between males. P male 8 had two
bands not shared with any individual within the
study population; trapping records indicate that pmale 8 fledged from the Befotaka 3 nest in 1993.
Befotaka 3. Band-sharing values indicated a po-
tential first-order relationship between female 6
and male 150, but not between female 6 and male
48. Band-sharing suggested that the males were un-
related.
Soamalipo 2. Band-sharing values indicated a po-
tential first-order relationship between female 103
and a male 5, but not between female 103 and the
two subordinate males (P 136 and 7 30). Band-
sharing between a male 5 and 7 male 30 indicated
a potential first-order relationship.
Relatedness estimates between nests. Comparingamong nests, we observed high band-sharing val-
ues between female 121 (Befotaka 2) and female
103 (Soamalipo 2), male 5 (Soamalipo 2) and male
48 (Befotaka 3), and between male 34 (Ankerika
4) and female 6 (Befotaka 3) ,suggesting potential
first-order relatedness between these pairs of
adults.
Discussion
Subordinate males may have fathered all nest-
lings in this study. At Soamalipo 2, one subordinate
male appeared to have fathered both nestlings,
however, because a male 5 and 7 male 30 are close
relatives, and because of missing data for a male
5, we cannot exclude a male 5 as a possible father
of one or both nestlings. At all nests, paternity by
subordinates could have occurred by chance, as all
attending males copulated with the female (Tingay
2000). Paternity by subordinates was surprising giv-
en that dominant males invested more energy to
the nesting attempt than subordinate males (Tin-
gay 2000). This level of dominant male investment
may be explained by the apparent first-order relat-
edness of the female and the dominant male at
three of four nests (Ankerika 4, Befotaka 3, and
Soamalipo 2). Because 50% of alleles are shared
with a first-order relative, and 25% with an off-
spring of a first-order relative, then shared alleles
are transmitted to the next generation if a first-
December 2002 Reiatedness of Madagascar Flsh-Eagles 283
Table 1. DNA fingerprinting hybridization bands (Jeffreys 33.15 probe) observed for individual Madagascar Fish-
Eagles. Bands are designated by enzyme used (H = Hae\\\ or R = Rsai) and molecular weight of bands in kilobase
pairs. Sex and rank for individuals is indicated (F = female, aM = alpha male, pM = beta male, yM = gamma male,
NSL = nestling, JUV = juvenile).
Ankerika 4^ Befotaka 2'’ Befotaka 3'= Soamalipo 2^
F aM (3M F aM (3M ;NSL F aM? aM? JUV F aM PM yM NSL NSLIndividual 113 31 34 121 118 8 47 6 150 48 128 103 5 136 30 68 00
Bands
H 16.0 + + + + + + + + + + 4 4 4 4 4 4 4H 10.7 -F + + 4 4H 8.5 + + + + + + + + + 4 4 4 4 4 4 4 4H 7.3 + + + + + + + 4 4 4 4 4 4H 6.5 + + + + 4H 6.0 -F -F -F 4 4H 5.7 + + + + 4 4H 5.6 + + 4H 5.2 + 4H 4.9 -F -F 4 4H 4.7 +H 4.5 + + + + + + + 4 4 4 4 4 4 4H 3.9 + + + + + + + + + 4 4 4 4 4 4H 3.6 -F -F -F + + 4 4 4H 3.2 + + + + + + + + 4 4 4H 2.9 + + + + + + + + + 4 4 4 4 4 4 4 4H 2.7 + -F + + + + + + 4 4 4 4 4 4 4 4H 2.6 + + + + -F -F -F -F -F 4 4 4 4 4 4 4 4H 2.2 + + + + + + -F + + 4 4 4 4 4 4 4 4H 1.5 + + + + + + + + + 4 4 4 4 4 4 4 4H 1.4 -F -F -F + -F -F + + + 4 4 4 4 4 4 4 4H 1.0 + + + + 4 4 4 4 4 4 4H 0.9 + + + + + + + 4 4 4 4 4R 12.0 + + + + + + + + + 4 4 4 ? 4 4 4 4R 5.2 -F -F -F -F ?
R 5.0 + + + + + + 4 ? 4 4 4R 4.7 + + 4 ? 4 4 4R 4.5 + ?
R 4.4 + -F -F -F -F 4 ? 4R 4.2 + ? 4 4R 3.3 + + + + + + + + 4 4 4 ? 4 4 4 4R 1.5 + + + 4 4 ? 4 4 4 4R 1.4 + + + -F -F -F -F 4 4 ? 4 4 4R 1.2 4 + + + + + + + + 4 4 4 ? 4 4 4 4
Total No. bandsper individual 21 21 22 20 20 22 26 21 21 20 19 21 14 19 21 20 23
^Fifteen bands are variable at Ankerika 4 (H 7.3, H 6.5, H 6.0, H 5.7, H 5.6, H 4.9, H 3.6, H 1.0, H 0.9, R 5.2, R 5.0, R 4.7, R 4 4,
R 1.5, R 1.4). All other bands are invariant.
Of the variable bands at Befotaka 2, six are shared between the nestling and the female (H 10.7, H 4.5, H 3.6, H 1.0, R 5.0, R 1 5),
six are shared between the nestling and the beta male (H 6.5, H 6.0, H 0.9, R 5.2, R 4.4, R 1.4); one is shared between the nestling,
female, and beta male (H 3.2); and four are variable but are not observed in tbe nestling (H 5.7, H 5.2, H 4.7, R 4.5). All other
bands are invariant.
Of the variable bands at Befotaka 3, four are shared between the juvenile and the female (H 7.3, H 6.5, H 3.6, R 4.7); and ten are
variable but are not observed in the juvenile (H 10.7, H 6.0, H 5.7, H 5.6, H 4.9, H 3.2, H 1.0, R 5.0, R 4.2, R 1.5). All other bands
are invariant.
Of the variable bands at Soamalipo 2, four are shared between nestling 68 and the female (H 7.3, H 3.9, H 3.2, R 5.0); two are
shared between nestling 68 and the gamma male (R 4.7, R 1.4); and one is shared between nestling 68, the female, and the gammamale (H 4.5). Five bands are shared between nestling 00 and the female (H 3.9, H 3.6, H 3.2, R 5.0, R 4.4); four are shared between
nestling 00 and the gamma male (H 0.9, R 4.7, R 4.2, R 1.4); and one is shared between nestling 00, the female, and the gammamale (H 4.5). Five are variable but are not observed in either nestling (H 10.7, H 6.0, H 5.7, H 5.2, H 4.9); and all other bands are
invariant.
284 Tingay et al. VoL. 36, No. 4
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Deciembkr 2002 REIATEDNESS of MADACiASCAR FiSH-EAGI.ES 285
order relative reproduces successfully. At Soamali-
po 2, the dominant male gained an additional ge-
netic advantage by having two potential hrst-order
relatives at the nest (the female and the y male).
It would be advantageous to be a male at the same
nest as a brother, because if either mated success-
fully, then shared genes are transmitted to the next
generation. Although a strategy of assisting repro-
ductive efforts of close relatives may be advanta-
geous for some Madagascar Fish-Eagles, apparently
it is not the only strategy in use. At Befotaka 2, the
dominant male was not the father, and nor was he
a first-order relative of either the female or the sub-
ordinate male.
At Befotaka 3, ajuvenile female did not disperse.
This is the hrst observed instance of a female nest-
ling from a previous year remaining at a nest (Ra-
fanomezantsoa 1997). Flere, delayed dispersal was
not associated with observed helping activity, yet
the female juvenile was tolerated at the nest. Al-
though inconclusive, our findings do not exclude
the delayed dispersal hypothesis.
Between-nest relatedness comparisons revealed
that some adults had a potential close relative (par-
ent-offspring or full-sibling) at another nest within
the study area. This suggests that hrst-order rela-
tives (excluding nestlings) are as likely to be found
among nests as within a nest.
We are currently investigating the full range of
breeding strategies in the Madagascar Eish-Eagle.
We intend to determine whether this species ex-
hibits genetic monogamy or polyandry by extend-
ing our sample size and duration of study. Studies
of another cooperative polyandrous raptor species,
the Galapagos Hawk {Buteo galapagoensis) has re-
vealed mixed paternity at nests over two consecu-
tive breeding seasons (Faaborg et al. 1995). How-ever, the dominance hierarchy we have observed
among cooperative hsh-eagles has not been docu-
mented among Galapagos Hawks, which may or
may not influence the occurrence of genetic mo-nogamy within polyandrous groups of Madagascar
Fish-Eagles. If delayed dispersal is obligatory in this
species, recolonization of unoccupied habitats mayhave to be promoted by active conservation mea-
sures, such as the translocation of individuals from
other areas. Additionally, copulation by closely-re-
lated pairs, as observed in this study, suggests that
the effects of inbreeding may have to be consid-
ered in conservation planning. For example, if
hrst-order relatives are found to be producing off-
spring, conservation managers may wish to target
some of those specific individuals as likely candi-
dates for translocation, in order to reduce the
probability of further inbreeding and to create an
opportunity for outbreeding with other, genetically
dissimilar, individuals.
Acknowledgments
We conducted this study under The Peregrine Fund’s
Madagascar Fish-Eagle and Wetland Conservation Pro-
ject. We thank the Madagascar Direction des Eaux et For-
ets, Tripartite Commission, Association Nationale pour la
Gestion des Aires Protogees and United Nations Educa-tional, Scientific, and Cultural Organization for collabo-
ration. This work was funded in part by grants from the
Liz Claiborne and Art Ortenberg Foundation, Environ-
ment Now, the John D. and Catherine T. MacArthurFoundation, Biodiversity Support Program, Hawk Moun-tain/Zeiss Optics 1999 Research Award, Jim Brett Global
Conservation Fund and University of Nottingham. Weare grateful to Professor David Parkin for technical assis-
tance with DNA purification, to Jim Berkelman and two
anonymous referees for their thoughtful comments onan earlier draft of this paper, and to Peregrine Fund Field
Manager Loukman Kalavah for expertise in the field
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© 2002 The Raptor Research Foundation, Inc.
NESTING AND PERCHING HABITAT USE OETHE MADAGASCAR FISH-EAGLE
James Berkelman^ and James D. FraserDepartment of Fisheries and Wildlife Sciences, Virginia Polytechnical Institute and State University,
Blacksburg, VA 24061-0321 U.S.A.
Richard T. WatsonThe Peregrine Fund, 5668 West Flying Hawk Lane Boise, ID 83709 U.S.A.
Abstract.
—
We documented Madagascar Eish-Eagle (Haliaeetus vociferoides) nest and perch use on lakes
and rivers and compared parameters of used trees to unused reference trees. Nest and perch trees were
broader and taller, had more unobstructed branches, and were less obstructed by adjacent trees com-
pared to reference trees. Perch trees also were more often deciduous than reference trees. Nest sites
had more shoreline perch trees than reference sites. Logistic regression models with tree height as the
independent variable distinguished nest and perch trees from randomly selected reference trees. Models
with number of perch trees along a 1.25 ha (50 m width) shoreline section distinguished nest sites from
reference sites. These models suggest that the presence of trees >15 m tall within 50 m of the shoreline
is a good predictor of Madagascar Eish-Eagle habitat use.
Key Words; Madagascar Fish-Eagle, Haliaeetus vociferoides; habitat; Madagascar, nest tree, perch tree, shore-
line.
USO DE HABITAT DE ANIDACION Y PERCHA DEL AGUILA PESCADORA DE MADAGASCAR
Resumen.
—
-Documentamos el uso de nidos y perchas para el aguila pescadora de Madagascar {Haliaeetus
vociferoides) en lagos y rios y comparamos parametros de arboles usados con arboles no usados de
referenda. Los nidos y arboles percha fueron mas anchos y mas altos, tenian mas ramas despejadas, y
estaban menos obstruidos por arboles adyacentes en comparacion con los arboles referenda. Los arboles
percha fueron ademas algunas veces mas deciduos que los arboles control. Los sitios nido disponian de
mas arboles percha costeros que los sitios de referencia. Los modelos de regresion logistica con la altura
de los arboles como variable independiente distinguieron los nidos y arboles percha de arboles control
seleccionados aleatoreamente. Los modelos con numeros de arboles percha cerca a 1.25 ha (50 m de
ancho) de la seccion de costa distinguieron los sitios nido de los sitios referencia. Estos modelos sugieren
que la presencia de arboles >15 m de alto dentro de 50 m de la linea costera es un buen pronosticador
del uso de habitat del aguila pescadora de Madagascar.
[Traduccion de Cesar Marquez]
With a population estimate of 99 breeding pairs
(Rabarisoa et al. 1997), the Madagascar Fish-Eagle
{Haliaeetus vociferoides) is one of the rarest birds of
prey in the world (Meyburg 1986). Until recently,
little was known about the species’ ecology and sta-
tus. Langrand and Meyburg (1989) noted that the
Madagascar Fish-Eagle used tall trees near water
for nests and foraging perches, but prior to this
study, there had been no detailed quantitative stud-
' Present address: Department of Wildlife Ecology, Uni-
versity of Wisconsin, 218 Russell Labs, 1630 Linden Dr.,
Madison, W1 53706-1598; e-mail address: jberkelman®
facstaff.wisc.edu
ies of Madagascar Fish-Eagle nesting or perching
habitat use.
Nelson and Horning (1993) estimated from sat-
ellite data that Madagascar’s forest cover had been
reduced to 10.4% of the island by 1990. Nest-site
availability is a key limiting factor for raptor pop-
ulations (Newton 1979). Also perch-tree distribu-
tion is a reliable predictor of Bald Eagle {Haliaeetus
leucocephalus) distribution on the Chesapeake Bay
(Chandler et al. 1995). Thus, we focused our study
on both nest and perch trees, along with the sur-
rounding habitat conditions. The objectives of this
study were to determine characteristics of nest
trees, nest sites, and perch trees used by Madagas-
287
288 Berkelman et al. VoL. 36, No. 4
Table 1. Sites where Madagascar Fish-Eagle nests and perches were investigated in the region of Antsalova, Mada-gascar, 1994. Site names are lakes unless otherwise indicated.
Site Latitude, LongitudeNumber oe
Eagle Pairs
Masiadolo 18°41'S, 44°28'E HBesara 18°41'S, 44°16'E 1
Soahanina River 18°46'-48'S, 44°16'~19'E 3^
Antsahafa 18°48'S, 44°29'E PMasama 18°50'-5TS, 44“28'-29'E 2
Tsiandrora 18°58'S, 44°38'E 1
Andranolava 1'’ 19°0'S, 44°2TE 1
Befotaka 19°1'-2'S, 44°24'-25'E 3
Soamalipo 18°59'-19°2'S, 44°26'-27'E 3^
Ankerika 19°T-2'S, 44'^27'-44°28'E 4
Andranovorimirafy 19°3'S, 44°27'E 1
Andranolava 2'^ 19°4'S, 44°25'E 1
Antsakotsako 19°6'S, 44°33'E 1^
Ampozabe 19°9'S, 44°40'E 1
Bevoay 19°9'S, 44°25'E 1
Manambolo River 19°8'-9'S, 44°44'-49'S 2
Maromahia 19°11'-12'S, 44°37'-38'E 1
Bejijo 19°12'-14'S, 44°32 -33'E 1
No nest was found for one of the fish-eagle pairs at five of the sites.
Two of the lakes in the study had the same name.
car Fish-Eagles and to develop predictive modelsto identify fish-eagle nesting and perching habitat.
SiUDY Area and Methods
We conducted the study during the first half of the
Madagascar Fish-Eagle breeding season from 21 May-14August 1994. We investigated fish-eagle nesting andpeiching habitat in a 3000 km^ area in the Antsalova re-
gion of western Madagascar (18°40'-19°15'S, 44^15'-
44°50'E) that included the drainages of the Manambolo,Beboka, and Soahanina rivers west of the Bemaraha Pla-
teau. Topography consisted of coastal plains and low roll-
ing hills with elevations ranging from sea level to 126 m.Soils were shallow and sandy, and the vegetation was a
patchwork of dry deciduous forest, savanna, wetlands,
mangrove swamps, and rice paddies. The climate was sub-
humid and tropical with a dry season from April-Octo-ber and a wet season from November-March. Mean an-
nual rainfall in the region ranged from 1000-1500 mm(Donque 1972).
We defined a nest tree as any tree in which we ob-
served nest construction, incubation, or brood rearing.
A nest site was the area within 300 m of the nest tree. Apeich tree was any tree in which we observed adult fish-
eagles perching. We measured nest and perch trees ofevery known Madagascar Fish-Eagle pair in the study area
(Table 1). Our perch-tree sample {N = 29) was larger
than our nest-tree sample (N = 24) because we did notfind a nest for five of the fish-eagle pairs.
We measured characteristics of fish-eagle nest trees
and randomly selected reference trees to determine if
trees used by fish-eagles differed from average large trees
(>20 cm diameter at breast height [DBH]) near the
same bodies of water. To compare nest and perch trees
to available large trees, we randomly selected a referencetree for each nest or perch tree. We selected trees at the
same distance from the water as the nest or perch tree
To do this, we measured with a hip chain the distance
from the nest tree to the nearest water (nest-water dis-
tance), from perch tree to nearest water (perch-water dis-
tance), and the distance along the shore between the
nest and perch trees (nest-perch distance). We then ran-
domly selected a shoreline reference point on the samebody of water as the nest tree that we had measured(within 1 .5 km along the banks for nest trees on rivers)
To select each nest reference tree, we went to the
shoreline reference point and moved inland a distance
equal to the nest-water distance and selected the nearest
tree >20 cm in DBH as our nest reference tree. We usedthe same shoreline reference point to select a perch ref-
erence tree by moving the nest-perch distance in the
same direction (left or right) along the shoreline as that
between the used nest and perch trees. We then movedinland the perch-water distance and selected the nearest
tree >20 cm in DBH as our perch reference tree. Weused 20-cm DBH as a minimum size for reference trees
based on the minimum size of Bald Eagle perch trees onthe Chesapeake Bay (Buehler et al. 1992).
We measured DBH of nest trees to the nearest cm andused a clinometer to measure height to the nearest me-ter. We counted branches in the tree canopy that we es-
timated to be >5 cm in diameter and unobstructed for
1 m above and below. We recorded arc of accessibility bystanding at the base of the tree and using a compass to
December 2002 Mada(;asc]AR Fish-Eagle Nests 289
measure the total arc (0°-360°) that was unobstructed by
other trees for an estimated distance of 10 m from the
trunk and 3 m below the tree’s crown (Buehler et al.
1992). We recorded nest-tree species and classified
growth form following Keister and Anthony (1983). Ourclassification was based on the location of the lowest fork
in the trunk, and whether the tree was dead. We classi-
fied growth form as large if the lowest fork was in the
lower third of the trunk, medium if the lowest fork was
in the middle third of the trunk, and small if the lowest
fork was in the upper third of the trunk. We recorded
growth form as dead top if the top third of the crown
was dead and as snag if the entire tree was dead andleafless, regardless of the location of the lowest fork in
the trunk.
We measured minimum distance of each nest tree to
water with a hip chain and minimum distance to humandisturbance, building, road, and fish-eagle nest frommaps and aerial photos. Human disturbances included
agricultural clearings, rice paddies, villages, tombs, andfishermen’s camps. Temporary, seasonal shelters that
were not used during the fish-eagle breeding season were
not considered buildings. There were no paved roads
and few motor vehicles in the area, and the most traveled
roads were traversed by less than one motor vehicle per
day, even in the dry season. Oxcarts frequently were used
to transport materials, so we recorded any oxcart track
as a road.
We considered trees ^6.1 m high and with ^30° ac-
cessibility from the shoreline to be potential perch trees
based on the smallest recorded perch tree used by Bald
Eagles on the Chesapeake Bay (Buehler et al. 1992). Wecounted perch trees within 50 m of the water along a 250
m shoreline section centered on the nest tree or refer-
ence tree (Chandler et al. 1995). We classified mean sur-
rounding canopy height to 5-m intervals ranging from 0-
25 m based on visual observation.
We measured the perch tree that we saw fish-eagles use
most frequently for foraging for each of the 29 fish-eagle
pairs in the study area. Eleven (37.9%) of the pairs were
observed for at least 6 hr, at least once per week during
the breeding season (May-October) in 1992, 1993, and1994 as part of a related study (Watson et al. 1999). Theremaining 18 (62.1%) pairs were observed for at least 6
hr, at least three times per breeding season from 1992-
94. We measured the same tree characteristics for perch
trees that we measured for nest trees.
We tested the null hypothesis of no difference between
trees or sites used by breeding Madagascar Fish-Eagles
and reference trees or sites for each of the numerical
variables using the Wilcoxon signed-ranks test. We paired
each fish-eagle nest or perch tree with the randomly se-
lected reference tree on the same water body. We did not
test for differences in distance to water because this was
a criterion for selecting reference trees. We used the chi-
square test of equal proportions to determine if fish-eagle
habitat use was different from expected use for the fol-
lowing categorical variables: tree species, deciduous ver-
sus evergreen trees, growth form, and surrounding can-
opy height. If >20% of expected values were <5, we used
the likelihood ratio chi-square test statistic (Agresti
1990).
We developed logistic regression models to predict the
probability of fish-eagle use of trees and sites based onthe measured habitat variables using stepwise analysis
Our significance level for variables to both enter and exit
models was P = 0.05. We used dummy variables for
growth form categories in the logistic regression (Hos-
mer and Lemeshow 1989). We constructed classification
tables for each logistic regression model by using the es-
timated logistic probabilities for each tree or site to pre-
dict fish-eagle use (Hosmer and Lemeshow 1989). Weconsidered trees or sites as correctly classified as used hy
fish-eagles if the predicted probabilities were ^0.5.
Resui.ts
Nest-tree Characteristics. Nest construction, in-
cubation, or brood rearing was observed at 21
(87.5%) of the 24 measured nest trees in 1994.
The remaining three nest trees were used in 1993,
but not in 1994. Nest trees were taller, had moreunobstructed branches, and a greater arc of acces-
sibility than reference trees (Table 2). Mean nest-
tree DBH was more than twice that of reference
trees. Twenty-two of 24 (91.7%) nest trees versus
only 14 of 24 (58.3%) reference trees had a >270°
arc of accessibility.
Nest-tree species included Tamarindus indica {N= 7), Cordyla madagascariensis {N = 4), Adansonia
sp. {N — 2), Colvillea racemosa {N — 2), Neobeguea
mahafaliensis {N = 2), Acacia sp. {N = 1), Albizia
greveana {N = 1), Alleanthus greveanus {N =1), Foe-
tidia sp. {N = 1), Pandanus sp. {N = 1), and un-
identified {N = 2). T indica was, the most frequent-
ly recorded species of nest reference tree {N = 6).
Its proportion among nest trees (29.2%) was not
different from its proportion among reference
trees (20.8%) (x^ - 0.44, df = I, P = 0.51). Pro-
portions of nest trees and reference trees in each
growth form class were similar (x^ — 4.58, df — 4,
P — 0.33). Eight of the nest trees (33.3%) and
three (12.5%) of the reference trees were decidu-
ous (x^ = 2.95, df = I, P= 0.09).
Eish-eagle nest-tree use was positively associated
with tree height, producing a logistic regression
model of
0 = 1/1+ exp 5.52 - X 0-38x,
where 0 is the probability of fish-eagle use and x,
is the height of tree i. This model correctly classi-
fied 83.3% of 48 trees measured.
Nest-site Characteristics. Number of shoreline
perch trees was greater at nest sites than at randomsites (Table 3). There was a positive relationship
290 Berkelman et al. VoL. 36, No. 4
Table 2. Characteristics of Madagascar Fish-Eagle nest trees, perch trees, and paired reference trees in the region
of Antsalova, Madagascar in 1994.
Variable
Nest Trees
(V = 24)
X ± SE
(Range)
Paired
Reference
Trees
(N = 24)
X ± SE
(Range) pa
Perch Trees
{N= 29)
X ± SE
(Range)
Paired
Reference
Trees
(N = 29)
X ± SE
(Range) pa
DBH (cm) 87.8 ± 11.8 38.4 ± 4.2 <0.001 65.3 ± 7.2 36.9 ± 3.3 <0.001
(29-245) (22-114) (27-270) (21-120)
Height (m) 18.7 ± 0.8 10.5 ± 0.9 <0.001 16.7 ± 0.8 9.8 ± 0.4 <0.001
(10.7-25.9) (5.0-23.3) (9.4-30.3) (4.9-15.8)
No. of branches’^ 5.5 ± 0.7 3.2 ± 0.8 0.021 7.9 ± 1.2 1.8 ± 0.4 <0.001
(1-14) (0-19) (2-39) (0-15)
Arc of accessibility 346.7 ± 5.4 260.2 ± 25.0 <0.001 336.7 ± 7.1 231.4 ± 21.4 <0.001
(265-360) (0-360) (190-360) (0-360)
* Wilcoxon signed-ranks test significance level.
Number of branches in the tree canopy >5 cm in diameter and unobstructed for 1 m above and below.
Arc (0°-360°) that was unobstructed by other trees ^10 m of the trunk and ^3 m below the crown (Buehler et al. 1992).
between fish-eagle nest-site use and the number of
shoreline perch trees. The model was
9 = 1 1 + exp 3.49 - 2
where 0 is the probability of fish-eagle use and
is the number of perch trees within a 1.25 ha (50
m wide) shoreline section centered on the point
on the shoreline nearest nest tree i. Correct clas-
sification of fish-eagle use for this model was 72.9%
of 48 sites. Minimum distance to human distur-
bance, minimum distance to nearest road, mini-
mum distance to nearest building, and minimumdistance to nearest fish-eagle nest did not differ
between nest sites and random sites (Table 3) . Theproportion of nest sites in each 5 m canopy height
interval did not differ between nest sites and ran-
dom sites (x^ = 4.93, df = 4, P = 0.30). Meandistance to water of nest trees was 70.8 m (SE =
12 6, range = 6.8-199.2 m).
Perch-tree Characteristics. Perch trees were larg-
er (DBH and height), had more unobstructed
branches, and had a greater arc of accessibility
than reference trees (Table 2). Twenty-six of 29
(89.7%) nest trees versus only 16 of 29 (55.2%)
reference trees had a >270° arc of accessibility.
Perch-tree species included Colvillea racemosa (N— 5), Ficus cocculifolia (N =
4), Neobeguea mahafal-
lensis (N = 3), Tamarindus indica (N = 3), Albizia
lebbeck (N — 2), Borassus madagascariensis {N —2),Cordyla madagascariensis (N =
2), Acacia sp. {N ~
1), Adansonia sp. (N = 1), Cedrelopsis grevei {N ~
1), Pandanus sp. (N — 1), Raphia sp. {N = 1), and
unidentified {N — A). T. indica was the most fre-
quently recorded perch reference tree species {N= 10). Its proportion among perch trees (10.3%)
was smaller than among reference trees (48.3%)
(x2 = 5.96, df = 1, P = 0.02).
Perch trees and reference trees had similar
growth forms (x^ = 8.04, df = 4, P = 0.09). Pro-
portion of deciduous trees among perch trees
(34.5%) was greater than among reference trees
(10.3%) (x^ = 4.86, df = 1, P = 0.03).
There was a positive association between fish-ea-
gle perch-tree use and tree height, producing a lo-
gistic regression model of
0 = 1 1 + exp 8.68 2
where 0 is the probability of fish-eagle use and
is the height of tree i. This model correctly classi-
fied 84.5% of 58 trees measured.
Disclissicjn
Nest-tree Use. Madagascar Fish-Eagles used nest
trees that were taller and had a greater DBH, moreunobstructed branches, and a greater arc of acces-
sibility than reference trees. The suhstantial differ-
ence between nest trees and reference trees in
mean height and DBH suggests that the fish-eagle
selects nest trees from among the largest trees
available near water. By placing its nests in the tops
December 2002 Madagascar Fish-Eagi.e Nests 291
Table 3. Characteristics of Madagascar Fish-Eagle nest sites {N = 24) and paired reference sites (N — 24) in the
region of Antsalova, Madagascar in 1994.
Variable
Nest Sites
x± SE(Range)
Paired Random Sites
X ± SE
(Range) pa
Minimum distance to human disturbance'^ (km) 0.8 ± 0.2 0.9 ± 0.1 0.742
(0-2.8) (0-2.8)
Minimum distance to building (km) 1.8 ± 0.4 1.8 ± 0.3 0.814
(0.1-7.7) (0-5.6)
Minimum distance to road (km) 1.7 ± 0.4 1.3 ± 0.3 0.055
(0-8.4) (0-5.4)
Minimum distance to fish-eagle nest (km) 4.8 ± 0.9 4.3 ± 0.9 0.104
(1.3-20.3) (0.4-20.1)
Number of perch trees'^ 30.8 ± 2.3 16.6 ± 1.9 <0.001
(10-53) (0-33)
Wilcoxon signed-ranks test significance level.
'’Human disturbances included agricultural clearings, rice paddies, villages, tombs, and fishermen’s camps.
Number of perch trees within a 1.25 ha (50 m wide) shoreline section centered on the point on the shoreline nearest the nest tree
We considered trees that we estimated to have a height ^6.1 m and >30° accessibility from the shoreline to be perch trees.
of these trees, it maximizes accessibility and visibil-
ity for foraging and territorial defense. These re-
sults were consistent with those reported for other
nesting Haliaeetus species (McEwan and Hirth
1979, Andrew and Mosher 1982, Anthony andIsaacs 1989, Shiraki 1994).
Nest-site Use. Number of shoreline perch trees
was the only variable that differed between nest
sites and random sites. This suggests that the Mad-agascar Fish-Eagle, like the Bald Eagle (Chandler
et al. 1995), may avoid areas without a sufficient
number of foraging perches.
Perch-tree Use. Perch trees were larger in height
and DBH, and had more unobstructed branches,
and had a greater arc of accessibility than refer-
ence trees. Such trees probably have greater access
and provide better visibility over water than other
trees. This is consistent with Bald Eagle perch-tree
use (Stalmaster and Newman 1979, Steenhof et al.
1980, Buehler et al. 1992). Madagascar Fish-Eagle
perch trees were more often deciduous than ref-
erence trees. In contrast with the nest-tree results,
the fish-eagles in this study appeared to avoid T.
indica for perching. T. indica is evergreen and often
has a dense crown; therefore fish-eagles may use
this species less often for perching than leafless
trees or snags.
Model Applications. The models we developed
may be used to identify Madagascar Fish-Eagle
nesting and perching habitat along lakes, rivers,
and estuaries in western Madagascar. They do not
apply to a sub-population of at least 16 fish-eagle
pairs that nest on offshore islands at the north end
of the species’ range (Rabarisoa et al. 1997). Al-
though our sample size was limited, the 29 breed-
ing sites sampled represent 29.3%, of the 99 knownremaining Madagascar Fish-Eagle breeding sites
(Rabarisoa et al. 1997). Bald Eagle managementguidelines recommend conserving mature forest
around existing and potential nest sites (Anthonyet al. 1982, Wood et al. 1989). We offer guidelines
that are more specific to the range of tree sizes anddensities found in the tropical dry forest and sa-
vanna habitats that surround the lakes where Mad-agascar Fish-Eagles occur.
We recommend that areas with a >32/ha density
of trees >15 m tall should receive high priority for
Madagascar Fish-Eagle conservation. Probability
that a shoreline tree would be used by MadagascarEish-Eagles for nesting or perching can be calcu-
lated by inserting tree height into the correspond-
ing logistic equation (Fig. 1 ) . Similarly, number of
perch trees along a 1.25 ha (250 X 50 m) shoreline
section can be used to estimate the probability that
Madagascar Fish-Eagles will use the shoreline sec-
tion for nesting (Eig. 1). These models are best
used under the conditions that were present dur-
ing this study (e.g., same eagle population density,
same time of year) and apply to eagles nesting onlakes, rivers, and estuaries.
Presence of tall trees close to shoreline is the
best predictor of Madagascar Eish-Eagle nest-site
use. The eagles often used the tallest trees near
water both for nesting and for foraging perches.
Rabarisoa et al. (1997) conducted MadagascarFish-Eagle surveys from 1991-95, and found areas
Probability
of
Use
292 Berkelman et al. VOE. 36, No. 4
Nest-tree Height (m)
Perch-tree Height (m)
0 S 10 15 20 25 30 35 40 45 50
No. of Perch Trees
Figure 1. Probability of Madagascar Fi.sb-Eagle use of iiesl trees, perch trees, and nest sites as a I’unclion of nest-
tree height (A), perch-tree height (B), and number of shoreline perch trees (C), in the region ol Antsalova Mada-
gascar, 1994. Probabilities were calculated by inserting dilferent values of the explanatory variable (tree height or
number of perch trees) into the equation resulting from stepwise logistic regression analysis.
Dec.ember 2002 Madagascar Fish-Eagle Nests 293
with dense forest adjacent to water that were un-
occupied by fish-eagles. Watson et al. (1996) are
developing means to augment the hsh-eagle pop-
ulation and seek areas of unoccupied fish-eagle
habitat where young eagles may be released. Ourmodels may be used both to identify areas of suit-
able, but unoccupied, fish-eagle habitat and high
conservation priority areas of occupied habitat.
The Tsimembo Forest surrounding Lakes Befo-
taka, Soamalipo, and Ankerika, where the highest
density of fish-eagles is found (Rabarisoa et al.
1997), should receive highest conservation priority.
The human population density around the lakes
was low until recent years when large numbers of
fishermen began to migrate to the region (Watson
and Rabarisoa 2000). Increased harvesting of tall
shoreline trees by migrant fishermen will have a
negative impact on the fish-eagles. People use the
tallest trees available for dugout canoes and build-
ing materials (Watson and Rabarisoa 2000) andmay prevent regeneration of tall trees by harvest-
ing large amounts of fuel wood to preserve fish by
smoke drying. Deforestation probably has already
substantially reduced the amount of fish-eagle hab-
itat available, and as the human population contin-
ues to increase, available habitat will continue to
decrease unless steps are taken to conserve fish-
eagle habitat.
At^KNOWI TDGMENTS
The Peregrine Fund provided financial and logistical
support for this research. We thank C. Razafimahatratra,
G. Raoelison, J. Mampiandra, and L. Kalavah for help
with data collection. Thanks to J. Rajesy, R. Rabarisoa, R.
I.ewis, P. Ravonjiarisoa, and M. Razafindrakoto for ad-
ministrative and logistical support in Antananarivo and
in the field. We thank C.A. Haas, J.J. Ney, R.G. Oderwald,
D.F. Stauffer, R. Thorstrom, R. Tingay, and A.R. Harmatafor comments on the manuscript.
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, S. Tiiomsett, D. O’Daniel, and R. Lewis. 1996
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the Madagascar Fish-Eagle {Haliaeetus vociferoides) JRaptor Rei 30:21-27.
Wood, P.B., T.C. Edwards, Jr., and M.W. Collopy. 1989.
Characteristics of Bald Eagle nesting habitat in Flori-
da. /. Wildl. Manage. 53:441-449.
Received 30 November 2001; accepted 9 July 2002
J. Raptor Res. 36(4);294-299
© 2002 The Raptor Research Foundation, Inc.
USE OF VEGETATIVE STRUCTURE BY POWERFUL OWLS INOUTER URBAN MELBOURNE, VICTORIA, AUSTRALIA—
IMPLICATIONS FOR MANAGEMENT
Raylene Cooke and Robert Wallis^School ofEcology and Environment, Deakin University, Warrnambool Campus, Warrnambool, 3280 Australia
John WhiteSchool of Ecology and Environment, Deakin University, Melbourne Campus, Burwood, 3125 Australia
Abstract.—The Powerful Owl (Ninox strenua) is Australia’s largest owl and is considered of least concern
nationally. Although a number of studies have reported on the ecology of Powerful Owls inhabiting
forests, few have focused on these owls living in urban areas. We report on the characteristics of different
roost trees used by Powerful Owls in a continuum of habitats from urban Melbourne to the more
forested outskirts. Records of weather conditions and daily temperatures were also analyzed to deter-
mine whether the owls were selecting particular roost trees for specific climatic conditions. We found
that roost-tree height and perch height was highly correlated, with the owls always roosting in the top
one-third of the tree, regardless of the tree height. As ambient temperatnre increased perch height
decreased, and vice-versa, but owls always roosted in the top one-third of the roost tree. Powerful Owls
did not simply move up and down the one tree, but moved to more suitable trees according to the
weather conditions. Hence, the species requires a structurally heterogeneous habitat to provide roost
trees for different temperatures. Eurtherraore, successful management of this species in the future will
require the protection of structurally diverse vegetation.
Key Words: Powerful Owl, Ninox strenua; disturbance, management, temperature, urbanization-, vegetation struc-
ture.
USO DE LA ESTRUCTURA VEGETATIVA POR NINOX STRENUA EN EXTERIORES URBANOS DEMELBOURNE, VICTORIA, AUSTRALIA—IMPLICACIONES PARA EL MANEJO
Resumen.—Ninox strenua es el biiho mas grande de Australia y es considerado nacionalmente de rnenor
interes. Aunque un numero de estudios se han concentrado en su ecologia en bosques, pocos se han
enfocado sobre los que habitan en areas urbanas. Reportamos las caracterlsticas del uso de diferentes
arboles percha utilizados por Ninox strenua en un continuum de habitats desde el Melbourne urbano
hasta los alrededores mas boscosos. Adicionalmente se analizaron los registros de condiciones climaticas
y temperaturas diarias para determinar si los buhos estaban seleccionando arboles percha particulares
debido a condiciones climaticas especificas. Encontramos que la altura de los arboles percha y la altura
de la percha utilizada estaba altamente correlacionados con el uso del tercio mas alto del arbol, sin
tener en cuenta la altura del arbol. Cuando la temperatura ambiente incrementaba la altura de la percha
decrecia, y viceversa, pero los buhos siempre percharon en el tercio mas alto del arbol percha. Los
buhos no se movieron simplemente hacia arriba y ab:qo del arbol, sino que se movieron a arboles mas
adecuados de acuerdo a las condiciones climaticas. Por lo tanto, la espccie requierc un habitat estruc-
turalmente heterogeneo que provea arboles perchas para diferentes temperaturas. Ademas de esto, el
manejo exitoso de esta especie en el futuro requiere de la proteccion de vegetacion estructuralmente
diversa.
[Traduccion de Cesar Marquez]
The Powerful Owl {Ninox strenua) is the largest
Australian owl. The male is slightly larger than the
female, growing to a length of 65 cm with a mass
^ E-mail address: [email protected]
of up to 1700 g (Higgins 1999). The Powerful Owl
is a nocturnal predator, with a diet consisting al-
most exclusively of medium-sized, arboreal, mar-
supial prey (Webster et al. 1999, Cooke et al. 2002).
The Powerful Owl is classified nationally as of
294
December 2002 The Powfrfue Owe in Urban Environments 295
“least concern” (rated nationally of conservation
significance, but at the lowest level, Garnett and
Crowley 2000) ,occurring at low densities in south-
eastern continental Australia. Within the state of
Victoria the species is listed as endangered (De-
partment of Natural Resources and Environment,
Victoria 1999) and threatened within the Greater
Melbourne Area (Mansergh et al. 1989). Estimates
of population numbers in the state of Victoria are
less than 500 pairs across the state (Garnett and
Crowley 2000).
The Powerful Owl was once considered to be a
specialist in ecological terms because of its appar-
ently restricted habitat and dietary requirements
(Fleay 1968, Seebeck 1976, Roberts 1977), indicat-
ing that it is vulnerable to habitat modihcation and
that it has specific conservation needs. Recent
studies, however, have contested these earlier find-
ings and consequently have questioned the degree
to which the Powerful Owl is vulnerable to habitat
modification and disturbance (Debus and Chafer
1994, Kavanagh and Bamkin 1994, Pavey et al.
1994, Cooke et al. 1997, Cooke et al. 2002).
Urban and suburban areas surrounding Mel-
bourne have been mostly cleared throughout the
past 100 years, with only small patches of remnant
vegetation remaining. Surprisingly, Powerful Owls
still remain in some urban areas, with one knownbreeding pair located only 18 km from central Mel-
bourne. Powerful Owls have also been recorded
living in close proximity to other Australian cities,
including Brisbane (Pavey et al. 1994, Pavey 1995)
and Sydney (Rose 1993). Tittle research has been
undertaken to determine the resources these owls
require for long-term survival in urban environ-
ments. Here, we describe roost tree characteristics
and features of roosts used in urban and suburban
areas by Powerful Owls. Results from this study are
then used to identify management options for Pow-
erful Owls in urban areas. The results of this study
may also provide valuable information for the fu-
ture management of other top-order raptors with
similar ecological attributes in urban areas.
Study Areas
During this study, we examined how Powerful Owls
used the structure of vegetation in a continuum of en-
vironments ranging from urban Melbourne (two sites),
through the urban fringe (three sites), and into moreforested areas (one site). Each site was selected on the
basis that it had a confirmed breeding pair of owls pres-
ent for several years.
The two sites located closest to Melbourne were the
Yarra Valley Metropolitan Park (100 ha) and WarrandyteState Park (586 ha), which were urban parklands man-aged for public recreation and 18 km and 24 km north-
east of central Melbourne, respectively. Both parks have
been extensively modified in the past and now consist ot
riparian areas and the occasional patch of remnant trees
surrounded fry a matrix of revegetated woodlands.
The next three sites along the continuum were OneTree Hill Reserve (143 ha), Smiths Gully (2.4 ha), andSteels Creek (21600 ha). One Tree Hill Reserve andSmiths Gully are both located 35 km from central Mel-
bourne while Steels Creek is located 65 km from Mel-
bourne. These three sites are all dry, open forests andconsist primarily of different Eucalyptus spp. as upper can-
opy trees with Acacia spp. dominating the middle story.
These three sites are also regularly visited by people andalso show signs of disturbance.
The sixth site along our continuum was Toolangi State
Forest (35 000 ha), which is located 80 km northeast of
Melbourne. This forest is a relatively undisturbed wet
sclerophyll forest dominated by mountain ash {Eucalyptwi
regnans). Middle story species are less common in this
area; however, the understory is dominated by various
ferns and bracken.
Methods
A total of 1300 day visits were made to the six study
sites between 1996-99. During these visits the roost tree
in which the Powerful Owl was located was recorded
Roost trees were those in which Powerful Owls spent time
during the daylight hours.
Here, we examined the different roost trees used by
the Powerful Owl at each of the study sites and the char-
acteristics of each tree used. These included the species
of tree, tree height, and the diameter at breast height
(DBH). Records of weather conditions and daily temper-
atures were also analyzed to determine whether the owls
are selecting particular roost trees for specific climatic
conditions.
Each study site was visited at least once weekly over a
4-yr period and each roost tree was examined for the
presence of the Powerful Owl or evidence that an owl
had used the tree recently. Evidence of usage included
fresh whitewash (excreta) or regurgitated food pellets
Temperature and weather conditions were noted, regur-
gitated food pellets were collected and, in situations
where the Powerful Owl was using the roost tree, the
perch height was measured using a clinometer.
Resutts
The Powerful Owls used 179 individual roost
trees at the six study sites. Twenty different tree
species were used as roost trees. The main trees
used for roosting were Eucalyptus spp. (54%), Aca-
cia spp. (18%), and Leptospermum spp. (15%). Oth-
er roost trees were hazel pomaderris {Pomaderns
aspera), the introduced Monterey pine {Pinus ra-
diata),cherry ballart (Exocarpos cupressiformis )
,
Christmas bush {Prostanthera lasianthos), the non-
296 Cooke et al. VoL. 36, No. 4
Table 1. Roost-tree characteristics at each of the six study sites. Values represent mean ± 1.96 SE.
Site NTree Height
(m) DBH (cm)
Perch Height
(m)
Yarra Valley Metropolitan Park 22 15.7 ± 2.2 55.0 ± 12.2 10.2 ± 1.9
Warrandyte 29 13.3 ± 2.3 40.3 ± 11.3 9.6 ± 2.0
One Tree Hill 22 16.2 ± 1.9 48.8 ± 10.0 12.2 ± 1.9
Smiths Gully 24 12,7 ± 1.8 37.1 ± 9.7 8.1 ± 1.1
Steels Creek 23 16.1 ± 2.2 38.5 ± 5.0 10.3 ± 1.9
Toolangi 59 13.0 ± 2.1 49.7 ± 9.6 11.2 ± 1.8
Pooled data 179 14.4 ± 0.9 45.6 ± 4.4 10.4 ± 0.8
indigenous sweet pittosporum (Pittosporum undu-
latum), and swamp paperbark {Melaleuca ericifolia).
To determine whether the dimensions of roost
trees varied between sites we compared the tree
height, roost height, and DBH of roost trees at
each site (Table 1). Roost tree heights were not
different among the six study sites (T5 173 = 1.856,
P = 0.104), with the mean height of roost trees
being 14.4 m ± 0.9 m (±1.96 SE). Perch heights
between the six study sites also did not differ sig-
nificantly (fy 173 = 1.643, P = 0.15), with the meanperch height being 10.4 m ± 0.8 m (±1.96 SE).
There was also no significant difference in the
DBH of the roost trees between the six study sites
( 5 ,i 7s“ 1.52, P — 0.186). Overall, the mean DBH
was 45.6 cm ± 4.4 cm (mean ± 1.96 SE). These
results suggest that the trees used for roosting have
similar physical dimensions at each site even
though the tree species may differ between sites.
0.90
01 0.85'5
z$ 0.80
o 0.75
% 0.70Q.
&0. 0.65n
" 0.60
i 0.55£® 0.500. YVMP One Tree Hill Steels Creek
Warrandyte Smiths Gully Toolangi
Site
Figure 1. Perch heights as a proportion of tree heights
(mean ± 1 and 1.96 SE) at each of the six study sites.
Plots with the same letters indicate homogeneous groups
as revealed by the Student Newman-Keuls (P < 0.05).
YVMP = Yarra Valley Metropolitan Park.
Given the variety of tree species used by the owls
for roosting, we decided to determine whether the
roost trees were being used in a similar fashion
among sites. Specifically, the relationship between
perch height and tree height was examined. Over-
all, perch height was positively correlated with tree
height (r = 0.91, P < 0.001, N = 179). Hence,
although the species of roost tree varied, the owls
tended to perch toward the top of the selected
roost tree. The perch height as a proportion of
tree height varied significantly between sites (E5 173
= 17.76, P < 0.001). Perch heights at the Yarra
Valley Metropolitan Park, Warrandyte State Park,
Smiths Gully, and Steels Creek were lower within
the roost trees than those in Toolangi State Forest
(Student Newman-Keuls test, P < 0.05; Fig. 1).
Although the mean perch height as a proportion
of the tree height varied among sites, roost tree
height was a predictor of perch height within each
site (Fig. 2). High values at all sites (except
Smiths Gully) suggest that there was a strong and
consistent relationship between perch height and
tree height (Table 2).
To further understand this relationship, a com-
parison was made between perch height and dif-
ferent temperature and weather conditions. Whenthere was no precipitation a strong negative asso-
ciation between temperature and perch height was
found (Table 3), with the owls at all sites choosing
lower perch heights as the temperature increased.
On days where rainfall occurred this trend was less
evident, with the owls at most sites showing no con-
sistent association between perch height and tem-
perature (Table 3).
Discussion
The Powerful Owls inhabiting the six study sites
used 179 roost trees. Of these, 87% were from only
Perch
Height
(m)
Perch
Height
(m)
Perch
Height
(m)
December 2002 The Powereul Owl in Urban Environments 297
Yarra Valley Metropolitan Park Warrandyte State Park
Perch height = -1.78 + 0.76 * tree height Perch height = -1.05 + 0.80 * tree height
One Tree Hill Reserve Smiths Gully
Perch height » -2.48 + 0.90 * tree height Perch height = 2.51 + 0.44 * tree height
Tree Height (m)
Steels Creek
Perch height = -1.66 + 0.74 * tree height
Toolangi State Forest
Perch height = -0.38 + 0.89 * tree height
Figure 2. The relationship between perch height and tree height at each of the six study sites. Lines indicate the
regression lines with 95% confidence limits.
298 Cooke ei ai.. VoL. 36, No. 4
Table 2. Regression results of the relationship between
perch height and tree height at all sites.
Site B? df F P
Yarra Valley
Metropolitan Park 0.844 1, 20 114.71 <0.001*
Warrandyte 0.859 1,27 171.34 <0.001*
One Tree Hill 0.825 1, 20 100.33 <0.001*
Smiths Gully 0.463 1, 22 20.84 <0.001*
Steels Creek 0.718 1, 21 56.89 <0.001*
Toolangi 0.980 1, 57 2792.09 <0.001*
* Represents a significant relationship between perch height and
tree height.
three different genera, Eucalyptus (54%), Acacia
(18%), and Leplospermum (15%). The other 13%of roost trees consisted of a variety of genera that
were infrequently used by Powerful Owls. Overall,
Powerful Owls roosted in 20 different tree species
at the six study sites and in most cases the roost
trees used were the most common species at the
specific study site. This indicates that the Powerful
Owls in the Yarra Valley corridor are probably us-
ing abundant and available tree species rather than
selecting less common species.
Roost tree characteristics such as height, perch
height, and DBH did not differ between the six
sites. Roost tree height and perch height, however,
were highly correlated, indicating a direct relation-
ship between the height of the roost tree and the
perch height. Powerful Owls observed at all six
sites generally roosted in the top one-third of the
roost tree, regardless of the tree height.
Overall, these results suggested that Powerful
Owls roosted in a number of tree species and they
were most likely found in the most common tree
species. It is probable that Powerful Owls are gen-
eralists in terms of the tree species in which they
will roost. The fact that the roost tree characteris-
tics (e.g., perch height, DBH) were similar at all
sites suggested that there was some degree of se-
lection of individual trees that offer optimal roost
characteristics. This was particularly highlighted by
the relatively small number of roost trees used at
each site compared with the number of trees avail-
able.
When temperature and weather conditions were
considered in relation to roost tree usage, the re-
sults suggested that as temperature increased
perch height decreased, and vice-versa. On hot
days. Powerful Owls were roosting lower in shadier
sites and on cooler days they roost at higher levels,
possibly to absorb sunlight. However, independent
of the height of the roost tree the Powerful Owls
still roosted in the top one-third of the roost tree.
This result suggests that they require habitats with
a large degree of structural variation to provide
roost trees for different temperatures.
The choice of roost trees used by the Powerful
Owls in clear and rainy conditions was also exam-
ined. The results showed that there was no signif-
icant difference in the perch height used by the
Powerful Owls at five of the six sites on wet days.
Steels Creek was the only exception to this pattern.
At most sites, Powerful Owls roosted in slightly low-
er trees on rainy days. However, at Steels Creek the
Powerful Owls actually roosted in taller, canopy
trees on precipitation days. Thus, it would appear
that the height at which Powerful Owls roost in
different weather conditions was not as important
as the amount of canopy cover provided by the
specific roost tree.
Results from this study also suggest that the
structural diversity within a site is important, given
Table 3. Correlation rc.sults from comparisons of perch height and temperature on days with and without precipi-
tation.
Site
No PrECIEI J AI ION PRKCtEITAlION
r-VAt.t.iE P-VAITIE r-VAt.UE P-VAl.UE
Yarra Valley Metropolitan Park -0.80 <0.001* -0.03 0.875
Warrandyte -0.27 0.021* 0.06 0.714
One Tree Hill -0.87 <0.001* -0.06 0.065
Smiths Gully -0.68 <0.001* -0.39 0.006*
Steels Greek -0.45 <0.001* 0.62 <0.001*
Toolangi -0.59 <0.001* -0.18 0.112
* Represents a significant relationship between perch height and temperature.
December 2002 The Powerful Owl in Urban Environments 299
that the Powerful Owls may use trees of different
heights to regulate their temperature in relation to
climatic conditions. Unfortunately environmental
change accompanying urbanization often results in
less structural diversity in vegetation, which can
mean that Powerful Owls have less choice in suit-
able thermal environments. What effect loss of
structure will have on survival and reproduction is
largely unknown, but it may in part explain why
the Powerful Owl is rarely found in highly-urban-
ized areas.
This information is important for future man-
agement of the Powerful Owl because it suggests
that this species does not simply move to higher or
lower branches in the one tree; rather, it moves to
an alternative roost tree with more suitable struc-
tural characteristics when it changes heights.
Therefore, management of the vegetation in the
urban areas must ensure that there is structural
diversity in the vegetation. Currently, the focus of
vegetation management for the Powerful Owl has
been on maintaining old eucalypts (canopy layer)
.
However, this may not provide for the structural
resource requirements of this species. Vegetation
management for the Powerful Owls should, there-
fore, be expanded to include the obviously impor-
tant mid-story species such as Acacia and Leptosper-
mum.
Acknowledgments
We thank Alan Webster for his on-site help, particularly
for providing historical records, and for continual sup-
port and other assistance. We also thank the Holsworth
Wildlife Research Fund, the M.A. Ingram Trust, Birds
Australia, and Deakin University for providing financial
support. We also wish to acknowledge the constructive
suggestions provided by referees of this manuscript.
Literature cited
Cooke, R., R. Wallis, A. Webster, and J. Wilson. 1997.
Diet of a family of Powerful Owls Ninox strenua from
Warrandyte, Victoria. Proc. R. Soc. Vic. 107:1—6.
, R. Wallis, and A. Webster. 2002. Urbanization
and the ecology of Powerful Owls Ninox strenua in out-
er Melbourne, Victoria. Pages 100-106 in I. Newton,
R. Kavanagh, J. Olsen, and I. Taylor [Eds.], Ecology
and conservation of owls. CSIRO Publishing, Mel-
bourne, Australia.
Debus, S.J.S. and C.J. Chafer. 1994. The Powerful Owl
Ninox strenua in New South Wales. Aust. Birds (Sup-
plement) 28:20-38.
Department of Natural Resources and Environment,
Victoria, 1999. Powerful Owl Ninox strenua. Flora and
fauna guarantee act. Department of Natural Resourc-
es and Environment, Melbourne, Australia.
Fleay, D. 1968. Nightwatchmen of bush and plain. Jaca-
randa Press, Brisbane, Australia.
Garnett, S.T and G.M. Crowity. 2000. The action plan
for Australian birds. Canberra: Environment Austra-
lia, Australian Government. Canberra, Australia.
Higgins, PJ- 1999. Handbook of Australian, New Zealand
and Antarctic birds. Vol. 4. Oxford Univ. Press, Mel-
bourne, Australia.
Kavanagh, R.P. and K.L. Bamkin. 1994. Distribution of
nocturnal forest birds and mammals in relation to the
logging mosaic in south-eastern New South Wales
Biol. Conserv. 71:41-53.
Mansergh, I.C., C. Beardsell, S. Bennett, R. Brereton,
K. O’Conner, K. Sandiford, and M. Schulz. 1989.
Report on the sites of zoological significance in the
Upper Yarra Valley (western section) and Dandenong
Ranges. Arthur Rylah Institute for Environmental Re-
search, Tech. Rep. Ser. No. 90, Melbourne, Australia
Pavey, C.R. 1995. Food of the Powerful Owl Ninox strenua
in suburban Brisbane, Queensland. Emu 95:231-232.
, A.K. Smyth, and J. Mathieson. 1994. The breed-
ing season diet of the Powerful Owl Ninox strenua at
Brisbane, Queensland. Emu 94:278-284.
Roberts, G.J. 1977. Birds and conservation in Queens-
land. Sunbird 8:73—82.
Rose, A.B. 1993. Notes on the Powerful Owl Ninox strenua
in New South Wales. Aust. Birds 26:134—136.
Seebeck, J.H. 1976. The diet of the Powerful Owl Ninox
strenua in western Victoria. Emu 76:167-170.
Webster, A., R. Cooke, G. Jameson, and R. Wallis. 1999
Diet, roosts, and breeding of Powerful Owls Ninox
strenua in a disturbed, urban environment: a case for
cannibalism? Or a case for infanticide? Emu 99:80—83.
Received 31 December 2001; accepted 7 August 2002
/ Raptor Res. 36(4) :300-308
© 2002 The Raptor Research Foundation, Inc.
NEST-SITE SELECTION OF THE CROWNED HAWK-EAGLE IN THEFORESTS OF KWAZULU-NATAL, SOUTH AFRICA,
AND TAI, IVORY COAST
Gerard Malan^School of Life and Environmental Sciences, University ofDurban-Westville, PB X5400f Durban 4000, South Africa
SusANNE ShultzPopulation and Evolutionary Biology Research Group, School of Biology, Nicholson Building, University of Liverpool,
Liverpool L69 3 GS, United Kingdom
Abstract.—Structural characteristics of Crowned Hawk-Eagle {Stephanoaetus coronatus) nest sites were
compared between forests in KwaZulu-Natal province, South Africa, and the Tai National Park, Ivory
Coast, and key features of nesting trees and nest-placement sites were identified. Nest-tree heights and
nest heights differed appreciably between three tree groups with the highest being indigenous Tai trees
(x tree height = 52 m and x nest height = 36 m, N = 8 nests), followed by exotic eucalyptus (x = 44
and 22 m respectively, N = 10) and indigenous trees (x = 24 and 14 m respectively, N = 17) from
KwaZulu-Natal. All the nest trees in Tai were eraergents, whereas 11 of 17 indigenous nest trees and
only two of 10 eucalyptus were so in KwaZulu-Natal. Non-emergent eucalyptus nest trees were predom-
inantly edge trees that may have provided easier access for flying eagles. Overall, nest forks were moreaccessible for flying eagles than random forks, although access did not differ between nests located in
emergent and non-emergent trees. Crowned Hawk-Eagles transport long sticks and heavy prey items to
their nests and access was probably the most critical feature of both the nest tree and placement of the
nest. Wildlife managers must, therefore, ensure that lone-standing or emergent trees are cultivated and
conserved, and flight paths to nests are kept open to allow Crowned Hawk-Eagles continued and easy
access to their nests.
Key Words: Crowned Hawk-Eagle, Stephanoaetus coronatus; nest access; emergent trees; nest-site selection;
wildlife management.
SELECCION DEL SITIO NIDO DEL AGUILA CORONADA EN LOS BOSQUES DE KWAZULU-NATAL,SUR AFRICA, Y TAI, COSTA DE MARFIL
Resumen.—Las caracteristicas estructurales de los sitios nido de las aguilas coronadas {Stephanoaetus
coronatus) fueron comparadas entre los bosques de la provincia KwaZulu-Natal, Sur Africa, y el parque
nacional Tai, Costa de Marfil, y se identilicaron los rasgos claves de los arboles nido y de los sitios de
ubicacidn de los nidos. Las alturas de los arboles nido y las alturas de los nidos difirieron apreciable-
mente entre arbol y grupo de arboles siendo los mas altos los nativos Tai (x altura del arbol = 52 m yX altura del nido = 36 m, N = 8 nidos), seguido por eucaliptos exoticos (x = 44 y 22 m respectivamente,
N ~ 10) y arboles nativos (x = 24 y 14 m respectivamente, N = 17) de KwaZulu-Natal. Los arboles nido
de eucaliptos no emergen tes fueron predominantemente arbcdes de borde que podian proveer mas
facil acceso a las aguilas en vuelo. En conjunto, las horquelas en nidos fueron mas accesibles para las
aguilas que horquetas colocadas al azar, aunque el acceso no dilirio entre los nidos colocados en arboles
emergentes y no emergentes. Las aguilas coronadas transportan grandes ramas y presas pesadas a sus
nidos y probablementc el acceso fue el rasgo mas critico tanto para la seleccion del arbol nido comopara la ubicacion del nido. Los manejadores de vida silvestre deben, por lo tanto, asegurar que arboles
aislados o emergentes son cultivados y conservados, y que las vias de vuelo a esos nidos permaneceran
abiertas para permitir a las aguilas coronadas continuo y facil acceso a sus nidos.
[Traduccion de (iesar Marquez]
Tree-nesting raptors select nesting trees and nest
sites on the basis of certain structural features that
^ Present address: Department of Nature Conservation,
Pretoria Technikon, P.B. X680, Pretoria 0001, South Af-
rica; e-mail address: [email protected]
hide the nest from potential predators, insulate the
nest against adverse weather conditions, place the
birds close to their hunting habitats and allow
them easy access to the nest (Moore and Henny
1983, Speiser and Bosakowski 1987, Lilieholm et
al. 1993, Burton et al. 1994, Selas 1996, Malan and
300
December 2002 Nest-seee Selection oe the Crowned Hawk-Eagle 301
Robinson 2001). Larger raptors often nest in an
exposed position that allows easy access to and
from the nest to deliver long sticks and heavy prey
(Speiser and Bosakowski 1987, Burton et al. 1994).
To further facilitate access, large raptors nest in tall
emergent trees or large trees with open branch
structures that respectively allow them access to the
nest both above and within the canopy (Moore and
Henny 1983, Burton et al. 1994, Malan and Rob-
inson 2001). Unfortunately, these preferences
bring large eagles in direct conflict with man as
large trees often are selectively harvested for com-
mercial and subsistence purposes (Bijleveld 1974,
Watson and Rabarisoa 2000).
In the predominantly arid South Africa, the de-
pletion of indigenous forest habitats and the arriv-
al of commercial exotic Eucalyptus, Pinus, Acacia,
and Populus trees have had a mixed impact on the
abundance and distribution of tree-nesting forest
birds (Low and Rebelo 1996, Allan et al. 1997).
Although by 1997 the area under commercial pulp-
wood and sawlog plantations (15 186 km^) was four
times larger than the existing natural forests (Van
der Zel 1996, Anon. 1998), the very short rotation
intervals of plantations (8-16 yr) do not allow the
trees to attain the size necessary to support large
stick nests. However, isolated, non-commercial
stands of large exotic trees are used for nesting by
indigenous birds, including raptors (Steyn 1977,
Macdonald 1986, Malan and Robinson 2001). In
indigenous forests, the processes of deforestation,
forest fragmentation, and the selective removal of
big trees from remnant patches alter the size, struc-
ture, and availability of indigenous trees for nest-
ing (Tarboton and Allan 1984, Allan and Tarboton
1985, Seydack 1995, Vermeulen 1999).
In South Africa, the Crowned Hawk-Eagle {Ste-
phanoaetus coronatus) has recently become of for-
mal conservation concern and the status of the
species has changed to near threatened due to the
loss of its previously suitable, indigenous nesting
habitat to short rotation, exotic plantations
(Barnes 2000) . Throughout much of its range, the
Crowned Hawk-Eagle breeds in tall evergreen for-
ests but can also nest in deciduous forests and
woodland-forest mosaics (Tarboton and Allan
1984). These birds prefer large forest trees for
nesting and the nest is usually situated in a major
fork, 8-30 m above ground but can be as high as
46 m (Steyn 1982, Tarboton and Allan 1984, Brownand Amadon 1989). In South Africa, CrownedHawk-Eagles nest in exotic eucalyptus and pines,
in addition to indigenous trees, consisting of most-
ly White Stinkwoods ( Celtis africana) (Tarboton andAllan 1984, Boshoff 1988).
The objective of this study was to compare
Crowned Hawk-Eagle nesting sites in three tree
groups and to use this information to provide re-
source managers with silvicultural guidelines for
providing nest-placement sites and stands for
Crowned Hawk-Eagles. As the forests in the
KwaZulu-Natal province. South Africa, are relative-
ly small in size and patehy in distribution (Boshoff
1997, Midgley et al. 1997), nest site characteristics
of these forests were compared with those from the
extensive and continuous, indigenous forest of the
Tai National Park, Ivory Coast. These comparisons
clarify which structural features are most important
when selecting a nest site, and how flexible
Crowned Hawk-Eagles are with regard to these
characteristics. Second, for KwaZulu-Natal, we ex-
amine stand size to determine the minimal habitat
requirements and compare topographical features
with randomly-selected sites to determine the ea-
gle’s selectivity for these features.
Study Areas
In South Africa, Crowned Hawk-Eagle nest sites werelocated for study during forest surveys in the KwaZulu-Natal (29°S, 31°E). Indigenous tree stands were surveyed
in forests characterized by a 10-25 m high canopy, dis-
tinct vegetation strata and numerous dominant tree spe-
cies (Low and Rebelo 1996, Midgley et al. 1997). Themean annual rainfall in these forests range from 900-1500 mm. Indigenous nest trees were sampled in the Or-
ibi Gorge, Vernon Crookes, Krantzkloof, Harold John-son, and Dlinza Eorest nature reserves, Ithala GameReserve, Hluhluwe-Umfolozi Park, all areas managed by
the KwaZulu-Natal Wildlife, and the Umgeni Valley Na-
ture Reserve and Tanglewood Natural Heritage Site. Ex-
otic eucalyptus were surveyed in abandoned plantations,
self-sown stands, and planted trees in large domestic gar-
dens, but none were known from commercial sawlog or
pulpwood plantations.
In the Ivory Coast, all nest sites were located within a
50 km^ area around the Station de la Recherche en Ecol-
ogie Tropicale (SRET, 7°00'N, 5°50'W) near the western
edge of the park. The Tai National Park is the largest
continuous lowland forest in West Africa (454 000 ha)
and contains the last sizeable protected habitat for a
number of Upper Guinea Forest endemics (Gartshore et
al. 1995). The mean annual rainfall at the research sta-
tion is 1800 mm. The forest was selectively logged in the
early 1970s, but the structure is essentially indistinguish-
able from a primary forest. The main forest canopy is
30-40 m in height, with emergent trees reaching to over
60 m (Guillaumet 1994).
Methods
The authors and conservation ofhcers located 27
Growned Hawk-Eagle nests in KwaZulu-Natal and eight
302 Malan and Shultz VoL. 36, No. 4
m Tai. Of the nests in KwaZulu-Natal, 19 were found by
listening for the loud queee-queee soliciting calls of nest-
lings or by spotting large nests (Steyn 1982). Althoughthis non-systematic search method may bias the sample
toward accessible and conspicuous nests (Daw et al.
1998), the nest-site data include nests from a wide selec-
tion of forest and nest-tree types. Sampled nest trees werelocated in indigenous forests, exotic monocultures, andmixed forests, and nest tree species were grouped into
either indigenous or eucalyptus stands.
The following nest-tree characteristics were recorded
from each nest site: the tree diameter at breast height
(14 m, DBH) of all stems >22 cm in diameter; tree
height (T), nest height (N), height of the first foliage,
and the height of the first side branch (R, irrespective if
It was dead or alive) . All height measurements were taken
with a clinometer. For trees with buttresses {N =3), the
circumference of the tree, including the buttresses, was
measured at breast height, a diameter calculated and di-
vided by two as to provide a conservative estimate of
DBH. The percent nest height was the proportional dis-
tance the nest was placed from the top of the tree ((N/
T)100) and the percent first branch height was the pro-
portional height the first branch was placed from the top
of the tree ((R/T)100).
Nests were classified as being placed within or belowthe foliage. Each nest was scored as either being posi-
tioned in a main fork, against the main branch (i.e., pri-
mary axis, mainly vertical), or on a side branch (i.e., sec-
ondary axes, mainly horizontal). The number of
branches supporting the nest was also counted. Lastly,
the nest tree was classified as emergent if the branch andfoliage structure protruded above the surrounding for-
est.
For each nest tree, we identified large and open forks,
excluding the nest fork, which could possibly support a
Crowned Hawk-Eagle nest that was 2 m wide and 2.5 mdeep (Steyn 1982). Each of these forks was categorized
as being positioned in a central fork or crotch (i.e., be-
tween main branches), as against the main branch, or ona side branch, and numbered from tree bottom to top.
A random fork was selected from the category of the fork
that supported the nest (i.e., if the nest was against a
main branch, the random fork was selected from similar
forks). If the random fork was not available from the
category that supported the nest, it was selected from a
combined sample of the remaining two positions.
For each cardinal direction (N, E, S, and W), accessi-
bility of the nests and random forks were determined by
whether the flying eagle would have a 30 m unobstructed
approach on a horizontal plane. For a flying eagle, a
flight path to the nest obstructed by foliage and/orbranches thus qualified inaccessibility.
We sampled characteristics of the three trees closest to
the nest tree. The distance from the nest tree to each
surrounding tree was measured. We calculated the meanarea occupied by the trees by squaring the mean distance
of the three trees from the nest tree. We then converted
the result to the number of trees per hectare and cal-
culated a tree density estimate at the nest tree (Phillips
1959).
For KwaZulu-Natal nest trees, each nest was plotted ona 1:10 000 orthophoto (black and white aerial photo-
graph with 50 m contour lines) to calculate stand size
and shape. From this photo, the maximum length (A)
and maximum width (B; perpendicular to the maximumlength axis) of the nest stand was measured. All mea-surements from 1:10 000 orthophotos were rounded to
10 m to allow for a 1 mm measurement error. Stand
shape (S) was defined as the maximum stand width di-
vided by the maximum length, with values ranging fromone (square shape) to zero (elongated shape). Nest stand
shapes were grouped into square (Shape ^0.5) or elon-
gated (Shape <0.5). The surface area of planted forests
was calculated from orthophotos by measuring the stand
lengths and widths. The surface area of indigenous forest
stands could not be calculated from orthophotos because
the edges of indigenous forests were not defined clearly
and the surface area was, therefore, estimated as S = (A/2)(B/2)(tt). From the orthophotos, the nest trees werealso categorized as being located on the edge of the stand
(i.e., the first tree encountered on the edge of a forest
stand). Lastly, distances to water, road, and nearest hu-
man habitation were measured from the nest tree andone random tree selected from each nest stand.
All data were subjected to the Kolmogorov-Smirnovone-sample test of normality. If the distribution of the
data was found to be non-normal, the non-parametric
Kruskal-Wallis test or Mann-Whitney Latest was employedThe Tukey honest significant difference test for unequalsample sizes was employed to determine which groups
are particularly different from each other after a signifi-
cant Kruskal-Wallis test was obtained from the Analysis of
Variance. The Pearson’s Chi-square test was used to test
for patterns with categorical variables. All data were an-
alyzed using the Statistica software package (StatSoft
1995) and probability levels were set at a = 0.05.
Results
Of the 35 Crowned Hawk-Eagle nests analyzed,
10 were located in eucalyptus and 17 in indigenous
trees in KwaZulu-Natal, and eight in indigenous
trees in Tai. Indigenous nest trees identified in
KwaZulu-Natal included Ficus spp. (7), Chrysophyl-
lum viridifolium (3), Syzygium cordatum (2), Cussonia
spicala, Scholia brachypetala, and Celtis africana. Theexotic nest trees were all eucalyptus. Nest trees
identified in Tai included Lofira alata, Klainodoxa
gabonesis, Ceiba pentandra, and Alstonia boonei.
All tree characteristics measured differed amongthe three tree groups (Table 1). Tai and eucalyptus
nest trees were taller than KwaZulu-Natal’s indige-
nous trees. Tai nest trees were larger in diameter,
and had higher first foliage, side branches and per-
cent first side branch heights than trees from
KwaZulu-Natal. Nest heights differed among all
three tree groups, and the percent nest heights
were lower in eucalyptus than Tai nests (Table 1).
The number of branches that supported nests
did not differ among tree groups (Kruskal-Wallis
2,35 ~ 1.7, P = 0.41), and the eagles used on av-
December 2002 Nest-site Sei.ection c:>f i he Crowned Hawk-Eagee 303
Table 1. Crowned Hawk-Eagle nest-tree characteristics of eucalyptus and indigenous tree groups in KwaZulu-Natal
and Tai. Means ± one standard deviation and range in parenthesis. Values with the same superscripts indicate values
that differed significantly from each other in the three-way comparison.
Species Ciass
Indigenous
KwaZui.u-Natal
Eucai.yptus
RWAZuriJ-NAIAL
Indigenous
Tai NKruskal-
Wallis HDBH (cm) 93^' ± 29 126*> ± 32 234^'^ ± 66 35 21.6**
(40-151) (83-206) (167-344)
Tree height (m) 24ab + 5 44a + g 52'^ ± 14 35 25.7**
(T5-34) (34-54) (33-67)
Height of hrst 9“’ ± 6 12*’ ± 9 33^>'> ± 7 35 17.8**
foliage (m) (1-19) (6-27) (26-42)
Height of first side 9“ ± 6 15'’ ± 7 34’’ ± 9 35 17.8**
branch (m) (1-20) (6-25) (25-47)
Nest height (m) ]4ab + 3 22a<: + 7 ± 10 35 23.4**
(7-21) (13-35) (2.5-49)
Percent nest height 58 ± 14 52^' ± 13 71" ± 13 35 7.6*
(43-93) (36-67) (44-90)
Percent first side 36^' ± 21 32b2: 12 66"’’ ± 13 35
branch height (4-62) (16-47) (44-78)
^ihc = p <; 0.05, I'ukey tests.
* P < 0.05.
P < 0.001.
erage 3 ± 1 branches (A ± SD, N = 35 trees) to
nest on. Twenty-seven of 32 nests (84%) were
placed within the foliage (as opposed to under the
foliage), and placement of nests in relation to the
foliage was not associated with tree groups (x^
0.7, P = 0.70). In Tai, 63% of the nests {N = 8)
were placed on the lowest side branch, more fre-
quently than nests in indigenous (13%, N — \1)
and eucalyptus trees in KwaZulu-Natal (10%, N =
10, = 9.3, P< 0.01).
Of the 35 nests sampled, 20 (57%) were placed
m a central fork, nine (26%) on a side branch, and
six (17%) against the main branch; nest placement
was not associated with tree groups (x^ = 6.3; P —
0.17). Whereas seven (78%) of the nine side-
branch nests and four (67%) of the six main-
branch nests were from the most abundant fork
category, 18 (90%) of the 20 central-crotch nests
Table 2. The emergence of Crowned Hawk-Eagle nest
trees above the surrounding forest.
Emergent Nest Trees Yes No Totai.
Indigenous—KwaZulu-Natal 11 6 17
Eucalyptus—KwaZulu-Natal 2 8 10
Indigenous—Tai 8 0 8
Total (Percent) 21 (60) 14 (40) 35
were from trees where this fork type was not the
most abundant (x^ = 6.3; P < 0.001). Overall, 22
(63%) of the 35 nests were not placed in the most
abundant fork category and nest placement could
not be associated with the most abundant fork cat-
egory of the different tree groups (x'^ 1.0; P =
0.59).
The number of forks per nest tree did not differ
among the tree groups (1 1 ± 6 forks in indigenous
KwaZulu-Natal trees, 14 ± 8 in eucalyptus, and 7
± 3 in Tai nest trees; Kruskal-Wallis ~ ^-4? P= 0.16). Whereas the number of central forks per
tree did not differ among tree groups (1 ± 1, Krus-
kal-Wallis 772,35 = 3.2, P = 0.21), the number of
side forks did (indigenous KwaZulu-Natal 5 ± 4
forks, eucalyptus 2 ± 2, and indigenous Tai 3 ± 3;
Kruskal-Wallis 772 35 = 6.2, P< 0.05), although the
classes were not significantly different from each
other (Tukey tests, all P > 0.05). Eucalyptus had
more forks against the main branch (11 ± 8) than
indigenous trees in KwaZulu-Natal (4 ± 3) and Tai
(3 ± 1; Kruskal-Wallis = 9.6, P< 0.01; Tukey
tests, all P < 0.05)
.
All the nest trees in Tai and 11 of 17 indigenous
nest trees in KwaZulu-Natal were emergents,
whereas only two of 10 eucalyptus protruded above
the forest canopy (x^ = 12.2, P < 0.05; Table 2).
Overall, nests were more accessible to flying eagles
304 Malan and Shultz VoL. 36, No. 4
Table 3. The number of Crowned Hawk-Eagle nest
trees, with flight paths sampled in four cardinal direc-
tions, which allowed access to nest and random forks for
17 indigenous and 10 eucalyptus trees in KwaZulu-Natal,
and eight indigenous trees in the Tai Forest.
Number of
Flight Paths None One Two Three Four x^
Nest fork 0 1 12 12 10
Random fork 4 12 8 4 7 18.6**
** p< 0.001.
than were random forks (Table 3) . Access to nests
could not be associated with their placement above
(as emergents) or within the forest canopy (Table
4) . In KwaZulu-Natal, seven of the eight non-emer-
gent eucalyptus were located on the edge of the
nest stand, whereas, all the non-emergent indige-
nous trees were located inside the nest stands (x^
= 7.3, P< 0.01).
The mean distance from the nest tree to the
nearest three trees did not differ among tree
groups (indigenous KwaZulu-Natal 11 ± 6 m, eu-
calyptus 12 ± 8 m, and indigenous Tai' 13 ± 5 m;
Kruskal-Wallis 7^2,34 ~ 1-0, P = 0.62). The density
of trees at nest sites also did not differ among tree
groups (all trees 156 ± 175 trees/ha, indigenous
KwaZulu-Natal 172 ± 183 trees/ha, eucalyptus 189
±219 trees/ha, and indigenous Tai 85 ± 62 trees/
ha; Kruskal-Wallis 7^2,34 ^ 1-0, P = 0.62).
The areas of 1 3 Crowned Hawk-Eagle nest stands
in KwaZulu-Natal were not normally distributed
and were predominantly less than 50 ha in size (Ta-
ble 5). Nest stands were primarily small (20 m in
width and 30-50 m in length) and elongated in
shape (shape-index <0.5; Table 5). Sbape-index
values could not be associated with eucalyptus andindigenous tree stands (x^ = 0.12, P = 0.73).
Table 4. The number of flight path.s per CrownedHawk-Eagle nest tree, sampled in four directions, which
allowed access to nest forks in emergent and non-emer-
gent trees.
Number of
Flight Paths None One Two Three Four Total
Emergent 0 0 5 7 9 21
Non-emergent 0 1 5 3 5 14 2.4
Nest and random tree distances to topographical
features were not different for all variables whencomparing means (Table 6) and Crowned Hawk-Eagles were, therefore, non-selective regarding
these topographical features. One tree selected for
nesting was 20 m from an inhabited brick house
and another 10 m from a used bitumen road.
Discussion
Nest-site Selection. Tree-nesting raptors assess
variables such as vulnerability to predators, protec-
tion against adverse weather conditions, the cost of
nest building, structural features of the nest tree,
and access to the nest when selecting a site to build
their nest (Newton 1979, Moore and Henny 1983,
Bosakowski and Speiser 1994, Burton et al. 1994).
Whilst smaller raptors regularly conceal their nests
to avoid predation, larger raptors are less secretive
and customarily put their nests in exposed posi-
tions (Speiser and Bosakowski 1987, Selas 1996).
The large, 2-2.5 m wide and 2.5-3 m deep nests
of the Crowned Hawk-Eagle (Steyn 1982) are very
conspicuous.
Although large raptors generally do not hide
their nests as they can defend their nestling against
predators (Moore and Henny 1983), CrownedHawk-Eagles do suffer some nest predation fromprimates, especially if the nest tree can be accessed
Table 5. Statistical distribution of KwaZulu-Natal Crowned Hawk-Eagle nest-stand variables and shape index with
the Kolmogorov-Smirnov distribution test (K-S d) for normality.
DominantCafegory(Percent) Mean ± 1 SD Range N K-S d
Surface area (ha) 0-50 (77) 35.4 ± 73.7 0.05-250.15 13 0.42*
Maximum width (m) 20 (69) 253 ± 363 20-1090 13 0.34
Maximum length (m) 30-50 (69) 759 ± 987 30-3520 13 0.32
Shape (0.0-1.0) 0.2-0.3 (23) 0.39 ± 0.22 0.04-0.80 13 0.16
* P < 0.0.5.
December 2002 Nest-site Selection of the Crowned Hawk-Eagle 305
Table 6. Topographical characteristics measured from Crowned Hawk-Eagle nest and random trees in KwaZulu-
Natal {N = 13 nests).
Variables Nest Tree Random Tree
Distance to water (m) 83 ± 147 (10-550)^^ 159 ± 199 (10-520) 0.86
Distance to house (m) 859 ± 1661 (20-6250) 906 ± 1738 (20-6550) 0.24
Distance to road (m) 282 ± 277 (10-810) 285 ± 341 (30-1010) 0.11
* Mann-Whitney fTtest.
^ Mean ± 1 SD (range).
from nearby trees (Tuer and Tuer 1974, Kalina and
Butynski 1994) . This may be a reason why CrownedHawk-Eagles often select emergents for nest sites,
especially in Tai where eight diurnal monkey spe-
cies are found at very high densities (McGraw
1998). In Tai, the tall nest trees with their wide
bases and high, first side branches (mean = 34 mfrom the ground) may be extremely difficult, if not
impossible, for monkeys to climb (T. Struhsaker
pers. comm.). In KwaZulu-Natal, the presence of
fewer primate species (three at the most; Smithers
1983) may have resulted in reduced predation risk
for nestlings and might have allowed for the use
of lower and non-emergent trees.
Sites may also be selected for nesting because
the foliage protects the nest against adverse weath-
er conditions (Moore and Henny 1983, Bosakowski
and Speiser 1994). Crowned Hawk-Eagle nests are
usually situated within the leafy canopy, but the
birds also nest in exposed positions in partially col-
lapsed or dead trees (Steyn 1982, Tarboton and
Allan 1984, Kalina and Butynski 1994). In this
study, 32 nests were located in or below the foliage
and therefore sheltered, whereas the remaining
three nests, two of which produced young during
the study, were located in exposed positions in
dead trees. Hence, although there was a trend for
the birds to nest in a sheltered position, other fac-
tors, such as the availability of suitable nesting sites
and the cost of building a new nest, probably in-
fluenced the continued occupation of a nest in a
dying or dead tree.
Lastly, tree-nesting forest raptors may select trees
for their size and structural features, such as a tall
and open canopy, that allow unobstructed access
to the nest (Speiser and Bosakowski 1987, Cerasoli
and Penteriani 1996). The Crowned Hawk-Eagle
may require a nest that is easily accessible as it
needs to fly to the nest carrying sticks up to 1.2 mlong and 8 cm thick (Steyn 1982). In addition.
Crowned Hawk-Eagles are capable of killing prey
3-4 times their body mass, such as bushbuck( Tra-
gelaphus scriptus; Daneel 1979), which they dismem-
ber and carry in parts to the nest. Brown (1966)
noted that, in the Karen Forest in Kenya, these ap-
proach flights were always above the canopy, very
laborious and broken into short 91-137 m stints so
as to rest between flights. Under these conditions,
access to the nest would be critical in order to de-
liver nesting material and prey to the nest. Nesting
above the forest canopy in an emergent tree en-
hances accessibility.
The large indigenous nest trees were simple in
structure and provided, on average, one central
fork, 3-4 forks against the main branch and 3-5
forks on side branches for the eagles to place their
nest. Notwithstanding, only 2-4 branches were
used on which to build these large nests, indicating
that big, primary and secondary forks were select-
ed and not the smaller, multi-stemmed forks from
within the canopy structure. Large raptors require
a large tree-fork (crotch) to place the nest in andthe more open branch structure may facilitate ac-
cess (Newton 1979). The exotic eucalyptus differed
from the indigenous nest trees in that they provid-
ed, on average, 1 1 more forks. This was largely due
to the single main-stem growth form of these com-
mercially-cultivated trees. Trees from these stands
were also largely of similar height, probably be-
cause trees in these single species stands were
planted simultaneously. As seven of eight non-
emergent, eucalyptus nest trees were located onthe edge of the nest stand, the eagles may circum-
vent the scarcity of emergent eucalyptus by select-
ing edge trees that have greater access to the nest.
In conclusion, because nests located within andabove the canopy were equally accessible, access
seemed to be the most critical feature identifying
a Crowned Hawk-Eagle nesting tree and site. Thefindings that indigenous nest trees in KwaZulu-Na-
tal did not differ from eucalyptus or indigenous
trees from Tai Forest in terms of tree density and
306 MaiAN AND Shui.tz VoL. 36, No. 4
central and side fork availability, may indicate that
indigenous trees with their multiple main stems
and open branch structure may be as accessible for
flying eagles as emergent or edge trees.
This study did not quantify the ‘openness’ and
accessibility of indigenous nest trees in KwaZulu-
Natal, particularly with regard to tree canopy di-
ameter and volume, branch spacing and diameter,
and branch angle as nests were often placed on
near horizontal branches. Also, we did not exam-
ine the inter-relationship between the largest-di-
ameter side branches (required to support the
large nests) and the position of the primary and
secondary forks below or just inside the foliage,
related to openness and improved access. We also
did not take into account the slope at the nest site
and aspect of the nest, as nests located on the
downhill side of the tree may have been more ac-
cessible to flying eagles. Given the floristic differ-
ences between forests in Tai and KwaZulu-Natal, a
comparison of nest sites Avith randomly selected
sites, conducted at each nest stand, would have fur-
ther contributed toward the understanding ofwhat
constitutes a suitable nest tree. Lastly, data on howeasy arboreal primates can climb nest trees, partic-
ularly from the base, would have added to our un-
derstanding of how successful Crowned Hawk-Ea-
gles are in eliminating the predation risk by
nesting in tall, emergent trees.
Recommendations. Wildlife managers need to
manage forests by balancing timber harvesting
with maintaining wildlife habitat and must employ
multi-resource plans to do so (Lilieholm et al.
1993, Vermeulen 1999, Malan and Robinson
2001). These plans should incorporate both prac-
tical and proactive management objectives to con-
serve nesting habitat for large eagles in exotic and
indigenous forests. Apart from silvicultural guide-
lines, other considerations must include the prox-
imity of nests to hunting habitat, their temporal
and spatial distribution, and tbe effects of humandisturbance on nesting eagles (Lilieholm et al.
1993).
In this study, because we could not obtain reli-
able data on the age of the nests and how manyyoung were fledged from each nest over time, wedid not compare the structural features of produc-
tive between unproductive nests. Although other
factors also influence productivity, e.g., experience
of breeders, prey abundance, and persecution
rates, the productivity analysis may have highlight-
ed subtle differences between suitable and unsuit-
able nest trees and nest-placement sites. Our rec-
ommendations should therefore be treated with
some caution, as nests included in this study might
have been found unsuitable on the long term be-
cause certain deficient nest features may have lim-
ited successful reproduction.
Nonetheless, the nest trees must have open-
branch structures and large tree-forks. As nest trees
are typically emergents or edge trees, these trees
can be cultivated by felling surrounding trees or
leaving the tall trees standing (Seydack 1995). In
this study more than half of the Crowned Hawk-
Eagle nests were positioned in a central fork, there-
fore, the techniques of coppice-reduction or selec-
tive pruning could be employed to cultivate a tree
with the preferred 2-4 main branches. As Brown
(1966) demonstrated, suitable nest trees can be
identified a priori, and managers can therefore im-
plement these techniques to ensure a continued
supply of suitable nest trees.
To qualify as a nest tree, commercial eucalyptus
should be managed to reach a minimum height of
34 m and DBH of 83 cm (i.e., minimum size se-
lected for nesting) . Indigenous trees selected must
attain a minimum height of 15 m and diameter of
35 cm. The mean stand density of 156 trees/ha can
be employed as a guideline for Crowned Hawk-Ea-
gle nesting habitat. Although exotic stands must be
managed to a minimum size so as not to encroach
onto indigenous vegetation, nest-tree stand size it-
self is nonessential. Furthermore, in plantations,
nest stands cannot be placed at random as raptors
often require nest trees to be located away from
certain topographical features (Andrew and Mosh-
er 1982, Malan and Robinson 1999). However, with
regard to the proximity of nests to human dwell-
ings, water bodies, and public roads, the CrownedHawk-Eagles of KwaZulu-Natal were remarkably
non-selective and tolerant. In fact, the city of Dur-
ban, located in this province, harbors 12 active
nests within its metropolitan boundaries. Inter-
stand distances were not recorded in this study, but
Crowned Hawk-Eagles are known to nest 1.8—4.0
km apart and, thus, require only a relatively small
patch of suitable hunting habitat (Tarboton and
Allan 1984, Allan et al. 1996, Mitani et al. 2001,
Shultz 2002). Given the size of some of the prey
these eagles hunt, nest stands must preferentially
be located near the hunting habitat so as to sbort-
en flight distances to the nest.
Because Crowned Hawk-Eagles use the samenest for 10 years or longer, often until the tree col-
December 2002 Nest-site Seitctton of the Crowned Hawk-Eagle 307
lapses (Brown 1966, Steyn 1982), suitable trees
should not be felled. If the nest stand or tree must
be harvested, the felling should be done outside
the birds’ breeding season (August-March) and 6-
12 months after the nestlings have fledged to allow
sufficient time for the young bird to become in-
dependent (Steyn 1982, Tarboton and Allan 1984).
Given that a nest takes 4-5 mo to build (Brown
1966), replacement nest trees, located in the vicin-
ity of the nest tree in use, should be cultivated long
in advance to provide a suitable alternative nest.
The Crowned Hawk-Eagle in South Africa has
been classified as near threatened because of past
exploitation of nest trees and the likely destruction
of nesting habitat in the near future (Boshoff et al.
1983, Barnes 2000). Occupied nests should be
closely monitored to assess the status of this species
and to collect data on what constitutes productive
nests. Large tree-nesting forest raptors will always
have few suitable trees to nest in as large trees and
forks are less abundant than smaller ones (Newton
1979). When nesting in large trees, eagles also
compete directly with humans for this scarce re-
source (Boshoff et al. 1983, Watson and Rabarisoa
2000). It is, therefore, no longer adequate simply
to protect forests for birds of conservation con-
cern, but specific efforts must be made to satisfy
the nesting requirements of the Crowned Hawk-
Eagle and other tree-nesting forest raptors; e.g., in
South Africa the Bat Hawk {Macheiramphus alci-
nus), Ayres’s Hawk-Eagle (Hieraaetus ayresii), and
Fasciated Snake-Eagle {Circaetus fasciolatus)
(Barnes 2000, Malan and Marais in press). Ulti-
mately, a species-specific management plan should
be developed for these and other tree-nesting for-
est birds and the maintenance of nest-tree struc-
tural and topographical features incorporated into
management decisions.
Acknowledgments
We want to thank Natal Portland Cement and the
KwaZulu-Natal Ornithological Trust for sponsoring this
project. We also thank KwaZulu-Natal Wildlife for allow-
ing us to work in their reserves and park. Bill Howells
and David Johnson were particularly helpful in locating
nest sites. Guy Tedder, Denise James, Martin Buchler,
Gavin Lorry, and Bill Walker also informed us of nesting
localities. In Tai, we thank Professor Ronald Noe for host-
ing the Crowned Hawk-Eagle project, the Centre Suisse
des Recherches Scientifiques, Centre de Recherche enEcologie, the Project Autonome pour la Conservation duParc National de Tai for logistical support, the Minstere
de la Recherche and the Direction de la Protection de la
Nature for permission to conduct the study. Funding (for
S. Shultz) was provided by the Raptor Research Foun-
dation, Inc., Leslie Brown Memorial Award, the Pere-
grine Foundation, a Wildlife Conservation Society Re-
search Fellowship, and the Leakey Foundation.
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Received 5 November 2001; accepted 2 August 2002
Short Communications
J.Raptor Res. 36(4):309-314
© 2002 The Raptor Research Foundation, Inc.
Juvenile Dispersal of Madagascar Fish-Eagles Tracked by Satellite Telemetry
Simon RafanomezantsoaThe Peregrine Fund, P.O. Box 4113, Antananarivo 101, Madagascar
Richard T. Watson ^ and Russell ThorstromThe Peregrine Fund, 5668 West Flying Hawk Lane, Boise, ID 83709 U.S.A.
Key Words: Madagascar Fish-Eagle, Haliaeetus vocifer-
oides; dispersal] satellite telemetry.
The Madagascar Fish-Eagle {Haliaeetus vociferoides) is
critically endangered (Stattersfield and Capper 2000)
with a small population limited to wetland habitats on
Madagascar’s western seaboard (Rabarisoa et al. 1997).
Observations of extra-pair adults at the nest and juveniles
m the territories of breeding pairs (Watson et al. 1996,
1999) suggest unusual behaviors that may occur as a re-
sult of overcrowding in limited suitable habitat, or if in-
nate, may reduce the species’ ability to disperse into un-
occupied habitat. In addition to the behavioral and
evolutionary significance of understanding these obser-
vations, the cause and consequence of this behavior mayaffect conservation interventions intended to prevent the
species’ extinction. We report the results of a pilot study
to measure the movements and habitat use of fledglings
after they left parental territories to better understand
post-fledging dispersal (Rafanomezantsoa 1998) and the
occurrence of extra birds at the nest, and to assess the
effect on dispersal of release of captive-raised birds (Wat-
son et al. 1996, 1999, Rafanomezantsoa and Kalavaha
1999).
The movements of raptors have been investigated for
decades mainly by banding, direct observation in limited
areas, or tracking using VHF radios (Meyburg and Mey-
burg 1999). Recently, satellite telemetry has provided a
method that makes possible the global location of birds
over an extended period. Satellite telemetry was consid-
ered the method of choice to study juvenile dispersal in
Madagascar Fish-Eagles which may reach maturity at 3-4
yr of age. In addition to the extended study period, ju-
veniles were expected to move distances greater than we
could follow with conventional VHE-radio telemetry be-
cause much of their range is inaccessible, especially dur-
ing Madagascar’s wet season when lowlands may flood
(Rafanomezantsoa 1997).
’ Corresponding author’s e-mail address: rwatson®
peregrinefund.org
Methods
This study occurred in coastal floodplain wetlands of
western Madagascar between the Manambolo River
(19°15'S, 44°30'E) and Soahany River (18°40'S, 44°30’E),
about 300 km west of the capital, Antananarivo. This area
lies within the Western Malagasy phytogeographical re-
gion (Humbert 1954), which is characterized by annual
rainfall from 1000-2000 mm, monthly mean tempera-
tures above 20°C, and elevations less than 800 m. Thewet season begins in October or November and lasts
through March. The dry season begins in May and lasts
through September or October. The climax vegetation is
tropical dry deciduous forest, but savanna grasslands,
maintained by burning, dominate the landscape (Gml-
laumet 1984). Most lakes in the region are floodplain
lakes whose surface area varies considerably between wet
and dry seasons (Kiener and Richard-Vindard 1972).
During the 1997 breeding season (May-December),Platform Transmitter Terminals (PTTIOO Series®; Micro-
wave Telemetry 2000, Inc., Columbia MD) with antennas
hxed at 45*^, were mounted with a backpack style harness
on two fledgling fish-eagles. One transmitter (PTT No3482) was mounted on a female that was rescued froman aggressive sibling, raised in captivity, and released at
fledging age (Watson et al. 1996, 1999). This bird was
released by hacking (a falconry term for the process of
release to the wild; Cade 2000) into unoccupied, suitable
habitat at Lake Mangily (18°30'S, 44°34'E). The second
PTT (No. 3480) was put on a male that fledged naturally
from a fish-eagle pair on Lake Ankerika (19°03'S,
44°27'E), about 65 km south of the first. PTTs were pro-
grammed for 8 hr on, 24 hr off for six cycles; 8 hr on,
96 hr off for 84 cycles; and 8 hr on, 240 hr off for the
remaining life of the transmitter, to gain more frequent
locations of movements made in the first year, followed
by less frequent locations for the remaining life of the
PTT, which we expected to be at least 4 yr.
Satellite telemetry uses the ARGOS Data Collection
and Location System (Meyburg et al. 1995). ARGOS as-
signs PTT locations a grade according to calculated pre-
cision. We used only locations graded as within 1000 mof actual position. ARGOS reports two locations, one be-
ing a spurious mirror of the true location. We deducedthe true location using either concurrent visual obser-
vations, likelihood of sequential locations, or known hab-
309
310 Short Communications VoL. 36, No. 4
itat at each location. Locations were plotted in chrono-
logical order on a topographical 1:100 000 map. The pro-
gram Ranges IV® (Kenward 1990) was used to calculate
distances moved and range areas based on minimumconvex polygons (MCP) around locations.
Results
PTT No. 3480 on the male operated for 282 d, from
1 Decemher 1997-8 September 1998, providing 70 us-
able locations. From these locations, the total MCP range
of the male was 1040 km^ (Fig. 1). Between the fledging
date on 13 October 1997 and 17 April 1998 (186 d), the
male moved in a relatively small area around its nest site.
During the wet season, from December-March, the male
visited small lakes and flooded lowlands to the south and
southeast of its nest site along the Manambolomaty River
and Lakes Kakobo and Antsohaly, covering an area of
156.4 km^. By 24 April 1998, the male had moved north-
northwest with one location near Lake Mangily (the fe-
male’s release site) on the way. For 76 d at the beginning
of the dry season, from 13 May 1998-28 July 1998, the
male was located in the vicinity of the Soahanina River
estuary, and associated ponds and mangroves, ranging
over an area of 540.5 km^. The maximum distance re-
corded from its nest was 51 km. By 5 August 1998 and
through 8 September 1998, when the last usable trans-
mission was received, the male was located again in the
vicinity of the nest where his parents were raising a nest-
ling.
The PTT on the female operated for 348 d, from 15
October 1997-28 September 1998, providing 40 usable
locations (Fig. 2). We received 21 usable locations from
15 October 1997-22 November 1997 when the PTTceased transmitting for unknown reasons. It then re-start-
ed 80 d later on 11 February 1998 and we received an-
other 19 usable locations through 28 September 1998.
About 95% of usable fixes were <5 km from the release
site. Direct observation conhrmed that the bird movedaround Lakes Mangily and Sarny until held observations
ended 13 March 1998 due to inaccessibility from flood-
ing. The maximum distance recorded from the release
site was 8.2 km and the mean distance was 2.6 km. Thefemale’s MCP range was 45 km^.
Discussion
Usable locations for the male were sufficient to deter-
mine several aspects of the bird’s movement. Locations
were usually received 10 or more days apart, which lim-
ited the amount of detail that could be gained from
them, Initial movements of the naturally fledged male
were distances of 5-18 km to sites that may be visible to
a soaring bird from its natal site. The male made one
large movement of short duration 51 km to the north-
west, where he remained for 76 d, making successive
short movements, until returning to his natal site. All ar-
eas visited were without territorial, breeding pairs. Themale did not visit prominent wetland areas within his
MCP range where human disturbance was high, such as
Lakes Bemamba and Antsohaly.
The released female’s range during the wet season, as
water flooded the surrounding lowland areas, included
Lakes Mangily and Sarny, other small lakes, and a portion
of the Miharana River. Compared to the male, the female
made only very short movements around the release site
While it is possible that the low number of usable loca-
tions influenced her measured range area, results were
spread throughout a similar period to those of the male
and observations by our field team confirmed her loca-
tions during much of the study period.
The differences in movement patterns of the male and
female are interesting. They may be related to sexual dif-
ferences in behavior, but there are a number of other
factors that could influence dispersal. For example, nat-
urally-raised and fledged compared with captive-raised
and released by hacking might affect their behavior. So-
cial interactions with neighboring conspecifics, the nat-
urally fledged male had at least 10 territorial pairs near-
by; whereas, the female had only one resident pair within
5 km, which could have caused a difference in dispersal
behavior. Also, distribution of food during the wet-season
floods might influence movements.
Habitats visited by both eagles were lakes, rivers, man-
groves, and lowlands temporarily flooded during the wet
season. We assume that movements of fledglings were
made in exploration of suitable foraging habitat because
there was no seasonal pattern to the movements, and
they were of short distance and duration relative to the
species’ capacity for flight.
Despite the potential of satellite telemetry to track
birds for up to 4 yr, because no signal was detected from
the PTTs after about 18 mo, we were unable to learn
more about the occurrence of extra birds at the nest be-
yond the observation that the male returned to its par-
ent’s territory about 10 mo after fledging and remained
there at least a month while the adults were caring for a
nestling. Since this study, direct observation of banded
birds, and molecular studies of their genetic relatedness,
have revealed far more information (Tingay 2000, Tingay
et al. 2002).
Tracking additional birds to increase sample size need-
ed to compare dispersal between naturally-fledged and
captive-reared and released juveniles, and document hab-
itat use during dispersal, has not been attempted. Thepractical difficulties and cost of captive rearing in Mad-
agascar, and the cost of satellite telemetry, precluded fur-
ther study. Few studies have been done on post-fledging
dispersal in raptors (e.g., Walls and Kenward 1994) or
comparison between captive-raised and naturally-fledged
birds (e.g., Amar et al. 2000) probably for similar reasons.
As satellite telemetry becomes more efficient and afford-
able, these areas of study may benefit.
Satellite telemetry provided us with a level of coverage
and continuity, especially for long-distance movements,
that we could not have achieved for the male using con-
December 2002 Short Communications 311
44° 30’
E
Figure 1 . Chronological movements and minimum convex polygon range of the male Madagascar Fish-Eagle fledged
from a nest on Lake Ankerika.
312 Short Communications VoL. 36, No. 4
Figure 2. Minimum convex polygon range of the captive-reared female Madagascar Fish-Eagle released by hacking
at Lake Mangily.
December 2002 Short Communications 313
ventional VHF radios and tracking from the ground. Wemay have achieved similar results by VHF-radio tracking
from an aircraft, but lack of landing fields and fuel in
the study area precluded this approach. The pro-
grammed on-off cycle of the transmitters provided fewer
useful locations than we expected. A longer (e.g., 12-24
hr) on-cycle might have generated more usable locations
m these birds that were more sedentary than migrating
raptors. For example, two migrating Bald Eagles {Hal-
iaeetus leucocephalus) with PTTs programmed for 8 hr on,
16 hr off, and 4 hr on, 44 hr off cycles generated 205
fixes in 136 d and 27 fixes in 119 d, respectively (Grubb
et al. 1994). A migrating Wahlberg’s Eagle {Aquila wahl-
bergi) with a PTT programmed for 8 hr on, 134 hr off
generated 104 locations in 234 d (Meyburg et al. 1995).
A 12-24 hr on-cycle would increase the chance of satel-
lites passing over an eagle in optimum position (such as
m flight) to receive the transmitter’s signal. Transmission
of usable locations ceased for unknown reasons well be-
fore their anticipated 4-yr lifespan. Unexplained periods
of no data received added to our uncertainty of the birds’
movements.
We believe satellite telemetry is valuable for tracking
the movement of large birds of prey; however, there are
several limitations. The accuracy of locations within the
PTT’s operational period varied from day to day. Theprecision of the location is known to be affected by sev-
eral satellite parameters and by the orientation, location,
and movement of the transmitter. PTTs are at present
larger and less streamlined than conventional VHF trans-
mitters, and require antennas that protrude at a 45° an-
gle rather than contour down the back and the tail of
the bird. Also, PTTs are .substantially more expensive,
though this cost may compare favorably with the cost of
data collection from VHF radios which require personnel
in the field and logistical support,
Resumen.—En 1997, colocamos radio transmisores a dos
polluelos de aguilas pescadoras de Madagascar (Haliaee-
tus vociferoides) para estudiar sus movimientos y uso de
habitat durante la dispersion post emplumamiento. El
macho partio naturalmente del nido de sus padres dur-
ante Octubre y nosotros liberamos la hembra criada en
cautiverio el 15 de Octubre. El rango del aguila machofue 1040 km^ entre el 1 de noviembre de 1997 y el 8 de
septiembre de 1998 (70 localizaciones) y se movio unadistancia maxima de 51 km desde su area natal, al norte
del rio Soahanina, El comenzo moviendose largas distan-
cias (>5 km) el 16 de Diciembre de 1997, permanecio
en la vecindad del estuario del rio Soahanina por 76 dias,
entonces retorno a la vecindad del nido (<5 km) el 5 de
Agosto de 1998. El rango de la Hembra fue 45 km^ entre
el 15 de Octubre de 1997 y el 28 de Septiembre de 1998
(40 localizaciones) y se movio una distancia maxima de
8.2 km desde el sitio de liberacion. Los rios, lagos, mang-
lares y zonas bajas temporalmente inundadas durante la
temporada humeda fueron visitados por ambas aguilas.
Sugerimos que los movimientos de los volantones se hi-
cieron para explorar habitats de forrajeo adecuados, ya
que no hay un patron estacional para los movimientos, y
fueron relativamente de corta distancia y duracion con
respecto a la capacidad de vuelo de la e.specie.
[Traduccion de Cesar Marquez]
ACKNOWLTDCiMEN'rS
This study was conducted by The Peregrine Fund’s
Madagascar Project with funding provided, in part, by
Environment Now, the Liz Claiborne and Art OrtenbergFoundation, the John D, and Catherine T. MacArthurFoundation, the Walt Disney Company Foundation, the
Little Family Foundation and other important contribu-
tors. The project received in-kind support from the Na-tional Aeronautics and Space Administration, UnitedStates Fish and Wildlife Service, and other partners. Weespecially thank David H. Ellis, Jon W. Robinson, andPaul Howey for their cooperation and support during
this project, and the constructive reviews of this manu-script byJames Berkelman, Mark Puller, and Robert Leh-
man.
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Rafanomezantsoa, S.A. 1997. Behavior and natal dis-
persal of fledgling Madagascar Fish-Eagles. Pages
403-412 in R.T. Watson [Ed.], Madagascar wetlands
conservation project. Progress report III, The Pere-
grine Fund, Boise, ID U.S.A.
. 1998. Contribution a 1’etude des comportements
et de la dispersion des jeunes pygargues de Madagas-
car Haliaeetus vociferoides (Desmurs 1845) dans le com-
plexe des 3 lacs d’Antsalova. Memoire de D.E.A. Univ-
ersite d’Antananarivo, Madagascar.
and L. Kalavaha. 1999. Transfert de jeunes Py-
gargues de Madagascar. Pages 115-123 in A. Andri-
anarimisa [Ed.]. Projet de conservation des zones
humides de Madagascar. Rapport d’avancement V,
1997-1998. The Peregrine Fund, Antananarivo, Mad-
agascar.
Statterseield, AJ. and D.R. Capper. 2000. Threatened
birds of the world. Lynx Edicions, Barcelona, Spain.
Tingay, R.E. 2000. Sex, lies, and dominance: paternity
and behaviour of extra-pair Madagascar Fish-Eagles.
M.S. thesis. University of Nottingham, U.K.
, M. CuLATR, E.M. Hallerman, R.T. Watson, and
J.D. Fraser. 2002. Subordinate males sire offspring in
Madagascar Fish-Eagle {Haliaeetus vociferoides) polyan-
drous breeding groups. /. Raptor Res. 36:280-286.
Wau.s, S.S. and R.E. Kenward. 1994. Movements of ra-
dio-tagged Common Buzzards Buteo buteo in their first
year. lUs 137:177-182.
Watson, R.T, S. Thomsett, D. O’Daniel, and R. Lewis.
1996. Breeding, growth, development, and manage-
ment of the Madagascar Fish-Eagle {Haliaeetus vocifer-
oides). J. Raptor. Res. 30:21-27.
, S. Razaeindramanana, R. Thorstrom, and S. Ra-
fanomezantsoa, 1999. Breeding biology, extra-pair
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Received 9 July 2001; accepted 28 June 2002
J. Raptor Res. 36(4) :315-319
© 2002 The Raptor Research Foundation, Inc.
Prey of the Peregrine Falcon {Falco peregrinus cassini) in
Southern Argentina and Chile
David H. Ellis^
USGS Patuxent Wildlife Research Center, HC 1 Box 4420, Oracle, AZ 85623 U.S.A.
Beth Ann SaboWildlife Forensics Services, P.O. Box 142613, Irving, TX 75014-2613 U.S.A.
James K. Fackler590 Davidson Road, Bow, WA 98232 U.S.A.
Brian A. Millsap
Fish and Wildlife Conservation Commission, 620 S. Meridian Street, Tallahassee, FL 32399 U.S.A.
Keywords; Peregrine Falcon; Falco peregrinus; Argentina;
Chile, Pallid Falcon; prey.
The Peregrine Falcon {Falco peregrinus cassini) in Pata-
gonia attracted wide interest two decades ago (Anderson
and Ellis 1981, McNutt 1984) when there was a focus on
determining the taxonomic position of the Pallid Falcon
(also called Kleinschmidt’s falcon and Tierra del Fuego
falcon; formerly named Falco kreyenborgi)
.
In 1981, how-
ever, the pallid falcon was confirmed to be a pale color
morph of the peregrine (Ellis et al. 1981, Ellis and Peres
1983), and since that time, little work has been conduct-
ed on this color morph. Continent-wide research has
continued and has yielded a fair understanding of the
breeding distribution of the Peregrine Falcon in South
America (Anderson et al. 1988, McNutt et al. 1988, Rise-
brough et al. 1990). Also, two preliminary food habits
studies on the peregrine have been completed in Pata-
gonia (McNutt 1981, Peres and Peres 1985). Together
those papers provided a list of 23 species observed as
prey, and McNutt (1981) listed another eight species
seen pursued (but not captured) by peregrines.
The purpose of this paper is to assemble all that has
been published on peregrine food habits for Patagonia
and Tierra del Fuego and to add to that list from our
1980 and 1981 expeditions.
Methods
In November-December of 1980 and 1981, we traveled
by motor vehicle searching for eyries in Chubut, Santa
Cruz, and Rio Negro provinces of Argentina and in Ma-gallanes, Chile. Although we accessed 16 eyries, somewere empty (prey remains sometimes scatter in the
wind), so our totals included prey from only 11 eyries.
We accessed eyries (normally by rope) and recovered re-
cent prey (feathers, feet, and bones with tendons at-
^ E-mail address: [email protected] or dcellis®
theriver.com
tached) but discarded those bones that were so bleachedthat they may be attributed to former occupants of the
eyrie. Most of the prey were identified from whole feath-
ers. No pellets were used in this anaylsis. We included
some feathers from the base of the eyrie cliffs, but ex-
cluded those that were likely molted by other occupants
of the cliff. For example, several of our eyries were in old
Black-faced (formerly buff-necked) Ibis {Tkeristicus cau-
datus) nests within active ibis colonies. Although ibis
feathers were frequently found near these eyries andeven though we occasionally observed peregrines pursu-
ing ibis, we viewed these attacks near eyries as displace-
ment activities. Only once did we include an ibis as prey
and this was after finding four fresh feathers within an
eyrie which was neither beneath an ibis roost nor near
an ibis nest. McNutt (1981) observed peregrines killing
nestling ibis.
No food habits study based on prey remains is without
bias (Marti 1987, Bielefeldt et al. 1992). For peregrines,
bias derives from the fact that many prey individuals are
missed because prey are normally plucked before arrival
at the eyrie and many defleshed carcasses are removedby the adults and deposited elsewhere. Also, several cast-
ings sometimes represent a single prey item. Commonprey are normally under represented in peregrine prey
tallies, including our sample, because of the difficulty of
totaling individuals. Our method was to derive a mini-
mum count from feet, bills, remiges, and rectrices. Forexample, a sample of 300 feathers and assorted other
remains from one species, and probably representing
dozens of individuals, may yield a much smaller mini-
mum count. Conversely, rare prey are likely to be over
estimated in most studies including this one, because a
single feather, bill, or foot can document prey that wasaccrued only once.
Prey were placed in plastic bags and air dried by open-ing the bags in a windless situation on sunlit days andfumigated prior to identification at the U.S. National Mu-seum (USNM: Smithsonian Institute). At USNM, we as-
sembled a synoptic series including all known and mostof the likely prey species. Because USNM does not have
examples for all plumages of all Patagonian birds, wecould not determine species on nine individuals.
315
316 Short Communications VoL. 36, No. 4
Table 1. Avian prey of the Peregrine Falcon in southern Patagonia and Tierra del Fuego.^’^ Numbers refer to
minimum number of items represented in remains. A plus ( + ) indicates that a taxa was documented, but the numberof Items was not reported. Nomenclature follows Sibley and Monroe (1990).
Family Scientific Name Common NameMcNutt198L^
Peres andPeres
19853
This
Study
3
Rheidae Rhea pennata Lesser Rhea + * 1*
Tmamidae Eudromia elegans Elegant Crested-Tinamou 2
Podicipedidae Podiceps major Great Grebe 1
Procellariidae Halobaena caerulea Blue Petrel +
Pachyptila belcheri Slender-billed Prion -t-
Pelecanoididae Pelecanoides magellani Magellanic Diving-Petrel -f
Pelecanoides sp. 3
Ardeidae Nycticorax nycticorax Black-crowned Night-Heron 1
Threskiornithidae Theristicus caudatus Buff-necked Ibis *7*4 1
Anatidae Chloephaga picta Upland Goose
Anas sp. 1
Anas flavirostris Speckled Teal 2 1
Anas platalea Red Shoveler 1
Falconidae Falco sparverius American Kestrel 2
Phasianidae Callus gallus domesticus Domestic Chicken 1*
Rallidae Fulica leucoptera White-winged Coot 1
Charadriidae Vanellus chilensis Southern Lapwing 1 -t- 3 & 2*
Charadrius falklandicus Two-banded Plover -f
Charadrius modestus Rufous-chested Plover -h
Oreopholus ruficollis Tawny-throated Dotterel 1 -f 7 & 1*
Scolopacidae Fimosa haemastica Hudsonian Godwit -f
Gallinago stricklandii Fuegian Snipe 1
Thmocoridae Thinocorus orbignyianus Gray-breasted Seedsnipe 2 -f 4
Thinocorus rumicovorus Least Seedsnipe 17 + 5
Laridae Sterna sp. 2
Sterna hirundinacea South American Tern +
Columbidae Zenaida auriculata Eared Dove 16
Metriopelia melanoptera Black-winged Ground-dove 1
Columba livia Rock Dove -f
Psittacidae Cyanoliseus patagonus Burrowing Parakeet 2
Enicognathus ferrugineus Austral Parakeet 4 1
Caprimulgidae Caprimulgus longirostris Band-winged Nightjar 1
Furnariidae Geositta cunicularia Common Miner 3
Upucerthia dumetaria Scale-throated Earthcreeper 2
Eremobius phoenicurus Band-tailed Earthcreeper 2
Cinclodes fuscus Bar-winged Cinclodes 1
Cinclodes patagonicus Dark-bellied Cinclodes 4
Feptasthenura aegithaloides Plain-mantled Tit-Spinetail 1
Tyrannidae Neoxolmis rufiventris Chocolate-vented Tyrant 1 + 2
Muscisaxicola macloviana Dark-faced Ground-Tyrant 1
Fessonia rufa Patagonian Negrito 1
Hirundinidae TachyrAneta nieyeni Chilean Swallow 2
Notiochelidon cyanoleuca Blue-and-white Swallow 2
Troglodytidae Troglodytes musculus Tropical House-Wren +
Sturnidae Mimus patagonicus Patagonian Mockingbird 1
Muscicapidae Turdus falcklandii Austral Thrush 2 -1- 2
December 2002 Short Communications 317
Table 1. Continued.
Family Scientific Name Common NameMcNutt198U
Peres andPeres
19853
This
Study3
Montacillidae Anthus correndera Correndera Pipit 1
Fringillidae Agelaius thilius Yellow-winged Blackbird 1
Sturnella militaris Pampas Meadowlark +Sturnella loyca Long-tailed Meadowlark 1
Molothrus bonariensis Shiny Cowbird 1
Phyrgilus gayi Grey-hooded Sierra-Finch 1
Phyrgilus fruticeti Mourning Sierra-Finch 3
Phrygilus unicolor Plumbeous Sierra-Finch 1
Melanodera melanodera Canary-winged Finch 1
Diuca diuca Common Diuca-Finch 3
Sicalis luteola Grassland Yellow-Finch 3
Carduelis barbata Black-chinned Siskin 1
Unknown 8 0 9
Total individuals 53+ unknown 102
Total identified
individuals 45 unknown 93
Minimum no. species 13 17 42
^ Not listed is a Kelp Gull (Larus dominicanus) observed as prey of a juvenile Pallid Falcon on 10 March 1979 (Ellis and Glinski 1980)
^ Nonavian prey include only a lizard {Liolaemus sp.) and a small rodent.
^ An asterisk (*) in these columns identifies prey that had not achieved adult size.
It is not certain that all 7 ibis were nestlings when taken.
We identified feathers by placing materials from oneeyrie in a shallow white box and from prior experience
sorted the feathers into piles tentatively assigned to a like-
ly taxon. A representative feather was grasped by forceps
then compared to specimens of likely donor species.
Once a good match for size, color, and pattern was
found, the pile of feathers was sorted to remove any that
did not represent this species and morph. Then the pro-
cess was commenced anew. After one of us completed anidentification for feathers without unique color patterns
(and most passerine primaries do not have bold color
patterns), a second person evaluated the feathers andconfirmed or rejected the identification. The most diffi-
cult materials often required an evaluation extending anhour or more before a certain match was found. Occa-
sionally, a feather had to be washed and blow dried be-
fore comparisons could be made. All identified materials
were bagged separately and archived.
In comparing feathers, it was often necessary to fan
the wing or tail on the museum skin; to do so without
tearing the skin required holding the appendage in
alignment with the body while deflecting the tip of the
feather with forceps. To aid in this process, we preparedflat skins with tail and one wing fanned for about 50 spe-
cies while in Argentina. For some other species, we mere-
ly placed wings, tail, feet, beak, and feathers representing
all body areas in a plastic bag. All specimens were deliv-
ered to the Argentine Museum of Natural Sciences,
Buenos Aires, Argentina, where the most valuable wereretained. The remainder were released for export andshipped to the U.S.A.
Results
From this and the previous two studies (McNutt 1981,
Peres and Peres 1985), we have documented a fair variety
of the prey taken by the peregrine in Patagonia. McNutt
(1981) identified 13 prey species and two other genera.
Peres and Peres (1985) noted 17 species, of which 10
were new (i.e., not previously noted by McNutt [1981])
The list from our study (Table 1) includes 42 species of
which 32 were not previously recorded. In summary, at
least 55 prey species in 26 families are known to be taken
by peregrines in Patagonia. To this can be added the
Kelp Gull {Larus dominicanus) recorded as prey of a ju-
venile Pallid Falcon seen on 10 March 1979 (Ellis and
Glinski 1980).
Discussion
Our list does not represent the full range of prey taken
by the Peregrine Falcon in South America, because first
of all, our study included only the southern fifth of the
distribution of this race. Second, other prey species are
known to be taken by this falcon in the Falkland Islands
(Cawkell and Hamilton 1961) and in more northerly re-
gions of South America (Hilgert 1988). Third, the low
numbers of individuals taken for common and likely prey
species (e.g., only two Austral Thrushes [Turdus falcklan-
dii\ and one Patagonian Mockingbird {Mimus patagoni-
cus)
)
suggest that much more variety will come from con-
318 Short Communications VoT. 36, No. 4
tmued sampling. The relationship between diversity (i.e.,
the number of species detected) and sample size can be
characterized as beginning with a 1:1 relationship but
with the plot soon leveling off and finally approaching
an upper asymptote (the true maximum in the numberof species taken) only after several hundred prey are tal-
lied (Heck et al. 1975, Marti 1987). At present, the total
for all three studies is less than 200 individuals. Further,
the two most commonly taken species in Table 1 were
represented by only ca. 23 and 16 individuals; before the
upper asymptote is reached, we expect that the numberof individuals of the most commonly-taken prey will ex-
ceed 100.
The list of species taken (Table 1) suggests that the
peregrine is prone to capture some prey on the ground.
The gosling was observed being taken on a gravel bar.
Surely, the young rheas, perhaps the tinamou, and likely
some of the other young birds in Table 1 were taken on
the ground. In addition to the avian prey tallied, we also
recorded one lizard {Liolaemus sp.) and a small mammal(Rodentia ca. 40 g); both of these would likely have been
taken on the ground (or kleptoparasitized) . In South
America there is no competing large falcon that hunts
terrestrial prey (i.e., like the Prairie Falcon [A mexicanus]
m North America and the Saker Falcon [A cherrug] in
Europe and Asia) that may constrain the Peregrine Fal-
con to an aerial foraging niche, so it was to be expected
that the peregrine in Patagonia would take quarry on the
ground more frequently than do some other races.
It is obvious from the variety of oceanic species on the
Peres list (Peres and Peres 1985; Table 1) that their study
emphasized coastal areas. Their sample was also from an
area where the pallid morph is relatively common (C.
Peres pers. comm.). Their results, in comparison with
our list for inland eyries, where the pallid morph is rare,
suggest that pallid and dark peregrines hunt different
prey. To document this potential difference (i.e., to com-
pare the foraging niches of two sympatric color morphs)
will surely be an interesting ecological study. Pallid and
normal birds appear very different in the field. Pallid
birds are less conspicuous and gull-like when seen be-
neath gray, overcast skies. We propose that the pallid
morph may have evolved when conditions were right for
a population of pale peregrines to live in isolation from
the population of normal peregrines further north on
mainland South America.
Resumen.—^A partir de publicaciones previas, conocemos
menos de 100 item presa que representan poco menosde 25 especies de aves para el halcon peregrine de la
Patagonia {Falco peregrinus cassini). Este estudio, incluye
presas de 11 nidos, anade 93 presas identificadas repre-
sentando 42 especies de aves (32 no reportadas previa-
mente), un lagarto, y un mamifero pequeno. Aunque do-
cumentamos una considerable variedad de presas para el
halcon peregrine en esta region, la frecuencia con la cual
nuevas presas fueron encontradas en cada nido visitado,
sugiere que la diversidad de aves tomadas fue mucho masgrande que la que se describe aqui. Esta alta diversidad,
en parte, resulta de variedades palidas y de color normal
que ocupan nichos de forrajeo un tanto diferentes.
[Traduccion de Cesar Marquez]
Acknowledgments
In 1980, the U.S. Air Force funded much of our travel
Our 1981 work was largely funded by the National Geo-graphic Society and an anonymous philanthropist. Wethank Peter Simpson, manager of Estancia Chacabuco,Rio Negro, Argentina, for logistical support. Phil Angleidentified the lizard. Jamie Jimenez, Clayton White, andDavid Whitacre reviewed and improved the manuscriptOur thanks to staff at the USNM for allowing space for
our synoptic series and patience during the extendedtime devoted to identifying prey.
Literature Cited
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, T.L. Maechtle, and W.G. Vasina. 1988. Thesouthern breeding limit of the Peregrine Falcon. Pag-
es 251-253 mT.J. Cade,J.H. Enderson, C.G. Thelan-
der, and C.M. White [Eds.], Peregrine Falcon popu-
lations: their management and recovery. ThePeregrine Fund, Boise, ID U.S.A.
Bielefeldt, J., R.N. Rosenfield, andJ.M. Papp. 1992. Un-
founded assumptions about diet of the Cooper’s
Hawk. Condor 94:427-436.
Cawkell, E.M. and J.E. Hamilton. 1961. The birds of
the Falkland Islands. Ibis 103:1-27.
Ellis, D.H. and R.L. Glinskj. 1980. Some unusual re-
cords for the Peregrine and Pallid Falcons in South
America. Condor 82:350-351.
and C. Peres. 1983. The Pallid Falcon Falco krey-
enborgi is a color phase of the Austral Peregrine Falcon
{Falco peregrinus cassini). Auk 100:269-271.
, C.M. Anderson, and T.B. Roundy. 1981. Falco
kreyenborgi: more pieces for the puzzle. Raptor Res. 15.
42-45.
Heck, K.L., Jr., G. van Belle, and D. Simberloff. 1975
Explicit calculation of the rarefaction diversity mea-
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havior of Peregrine Falcons in Guayllabamba, Ecua-
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populations; their management and recovery. ThePeregrine Fund, Boise, ID U.S.A.
Marti, C.D. 1987. Raptor food habits studies. Pages 67-
80 in B.A.Giron Pendleton, B.A. Millsap, K.W. Cline,
and D.M. Bird [Eds.], Raptor management tech-
niques manual. Natl. Wildl. Fed. Sci. Tech. Ser. No10 .
McNutt, J.W. 1981. Seleccion de presa y comportamien-
to de caza del Halcon Peregrino {Falco peregrinus) en
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Magallanes y Tierra del Fuego. An. Inst. Patagonia 12:
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. 1984. A Peregrine Falcon polymorph: observa-
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Condor 86:378—382.
, D.H. Ellis, C. Peres, T.B. Roundy, W.G. Vasina,
AND C.M. White. 1988. Distribution and status of the
Peregrine Falcon in South America. Pages 237-249 in
T.J. Cade, J.H. Enderson, C.G. Thelander, and C.M.
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management and recovery. Peregrine Fund, Boise,
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Received 7 January 2001; accepted 10 July 2002
J Raptor Res. 36(4) :320-323
© 2002 The Raptor Research Foundation, Inc.
An Elevated Net Assembly to Capture Nesting Raptors
Eugene A. Jacobs^
Linwood Springs Research Station, 1601 Brown Deer Lane, Stevens Point, WI 54481 U.S.A.
Glenn A. Proudfoot^Caesar Kleberg Wildlife Research Institute, Mail Stop 218, Texas A&M University-Kingsville,
Kingsville, TX 78363-8202 U.S.A.
Key Words: capture techniques-, dho-gaza; drop net, elevated
net, mechanical owl", mist net.
The use of a Great Horned Owl {Bubo virginianus) to
induce mobbing behavior, in combination with a net sys-
tem, has become the technique of choice for capturing
many species of nesting raptors (Hamerstrom 1963,
Bloom 1987, Bloom et al. 1992, Steenhof et al. 1994, Ja-
cobs 1996, McCloskey and Dewey 1999). However, some
species, and some individuals trapped previously, may be
reluctant to stoop at the owl when conventional tech-
niques (i.e., placing owl and nets near ground level) are
followed (Rosenfield and Bielefeldt 1993). In testing a
mounted and live Great Horned Owl to induce mobbing
behavior in American Kestrels {Falco sparverius)
,
Card et
al. (1989) found that the closer an owl decoy was placed
to the nest the more aggressive the kestrels became. Adecoy (mounted or live) placed near the nest of “trap
shy” Cooper’s Hawks {Accipiter cooperii) was more effective
than conventional techniques, but this method required
climbing tree(s) and was found to be time consuming
(Rosenfield and Bielefeldt 1993). Here we describe an
elevated net assembly that, in combination with an owl
decoy, proved successful for trapping five species of rap-
tors.
MATERIAI.S AND METHODS
The system consisted of an aluminum telescoping pole,
a horizontal cross bar, two vertical upright poles, a dho-
gaza type net (Clark 1981), and a mechanical owl
(equipped with two radio controlled servos that provided
movement to the owl’s head and perch) as described by
Jacobs (1996; Fig. 1). The cross bar that supported the
net assembly was a 3-m section of conduit tubing 2.5 cmin diameter. We used a commercially available conduit-
bending tool to form 90° angles 25 cm from each end of
the tubing, resulting in a “U ’’-shaped cross bar. A section
of sheet metal (45 cm X 45 cm) was then bent aroundthe cross bar to form a triangular bracket that enveloped
the cross bar. Using sheet metal screws, this sheet metal
envelope was attached to a 25-cm section of aluminum
‘ E-mail address: [email protected]
2 Present address: Department of Wildlife and Fisheries
Sciences, Room 210, Nagle Hall, Texas A&M University,
College Station, TX 77843-2258 U.S.A.
tubing 3 cm diameter at the center of the cross bar to
form a “T” that resembled the goal posts of most Amer-ican football fields. The “T” formation provided a stable
base for the net assembly and the diameter of the base
of the “T” allowed for quick insertion of the cross bar
to a telescoping pole. Two 2.2-m sections of conduit tub-
ing 1,8 cm in diameter were inserted into the upturned
ends of the cross bar to form the uprights that supported
the net. We used four tethered leads about 12 cm in
length, four metal rings (shower curtain rings) about 5
cm in diameter, and either wooden clothespins or mag-nets to attach the four corners of the net to the tops andbottoms of uprights. When clothespins were used, the
free ends of the tethered leads were held by clothespins
taped to the top two ends of the uprights. When magnets
were used, a metal washer tied to the free end of the
tethered leads provided support for the top two corners
of the net. The bottom two leads were attached to the
bottom of the uprights and remained stationary. Twometal rings were placed on each side of the net, one in
the top corner and one at the half-way point. The rings
attached the net to the uprights allowing the net to re-
main open during set-up, The rings also allow the net to
drop freely to the cross bar when a bird made contact
Once contact is made with the net, the net slides downthe uprights and creates a pocket entrapping the bird.
We inserted a 10-cm section of tubing (vertical, 1.1 cmin diameter) into the bottom of the owl’s perch and at-
tached a corresponding 30-cm section of tubing (0.9 cmdiameter) to the “T.” This was positioned so that about
15 cm of the tubing extended above the center of the
cross bar to support the owl’s perch.
The 2-8 m telescoping pole allowed us to adjust the
height of the net assembly to suit the nest site. Three guy
lines attached to the base of the “T” bracket stabilized
the net assembly when the telescoping pole was extendedto a height greater than 3 m. We used a 1-m section of
1 .3 cm diameter conduit tubing, hammered flat at oneend and cut to form a point, as support stakes for the
telescoping pole and 0.5 m stakes (fashioned the sameway) for the guy lines. Total cost of materials was ca. $250(U.S.); telescoping pole ($180), net (.$20), cross bar
($10), uprights ($10), anchor stake for telescoping pole
($10), guy lines and support stakes (.$10), and miscella-
neous material ($10).
Because vegetation structure varied among nest sites,
we elevated the net assembly to the maximum length of
the support pole (8 m) or to the highest feasible level
where tree branches blocked a greater extension. Thenet assembly was placed within 50 m of the nest tree, in
320
December 2002 Short Communications 321
Figure 1. Elevated dho-gaza net assembly used to trap small- and medium-sized raptors near their nests.
view of the nest and with a clear flight path around the
net. Great Horned Owl vocalizations and conspecific calls
were utilized to lure nesting raptors to the net system(Bloom et al. 1992). A concealed observer was positioned
nearby (<100 m) to operate the radio controls to the
mechanical owl and record the sex of the adults whenthey were detected in the nest area (<50 m of nest). Theobserver (s) was able to sex all American Kestrels andSharp-shinned Hawks (A. striatus) from plumage char-
acteristics or relative size compared to their mates (Clark
and Wheeler 1987). We reported trapping success by us-
ing the number of birds trapped, divided by the numberof birds “tested” (birds detected within 50 m of the nest)
multiplied by 100.
When trapping Ferruginous Pygmy-Owls {Glaucidium
brasilianum)
,
we modified this system by downsizing the
net assembly (cross bar and uprights) to 2 m X 1 m,replacing the dho-gaza with a shortened 2-shelf mist net,
and replacing the mechanical owl with a conspecific
mounted decoy. This modified setup was used as de-
scribed above (using lure to induce mobbing behaviorfrom nesting owls), or simply placed in front of the nest
cavity entrance to capture the adults as they entered the
cavity to feed nestlings. The elevated mist net was placedabout 1.5 m from the nest cavity’s entrance.
Results and Discussion
During the breeding seasons (1994-2001) this tech-
nique was “tested” on five species of small to mediumsized raptors. Overall, we successfully captured 73% (113
of 154) of the individuals “tested.” Our trapping success
322 Short Communications VoL. 36, No. 4
Table 1. Comparison of capture rates of elevated net with a mechanical owl, normal net with a mechanical owl, and
normal net with a live owl as a trapping technique for raptors.
Elevated Net with
Mechanical Owl(This Study)
Ground-level with
Mechanical Owl(Jacobs 1996)
Ground-level
with Live Owl
Red-shouldered Hawk 65% (30 of 46) 54% (15 of 28) 75% (199 of 264)1
Sharp-shinned Hawk 81% (34 of 42) 77% (48 of 62) —American Kestrel 70% (21 of 30) — 71% (15 of 21)2
97% (115 of 118)1
Cooper’s Hawk 67% (2 of 3) 60% (3 of 5) 52% (32 of 62)1
Ferruginous Pygmy-Owl 79% (26 of 33) — —' Data from Bloom et al. 1992.
^ Data from Steenhof et al. 1994.
was generally similar or slightly lower than studies using
a ground-level net set (height ^2.5 m) and live owl
(Bloom et al. 1992, Steenhof et al. 1994) and slightly
better than Jacobs (1996) found when using a normal
net set and a mechanical owl (Table 1 )
.
Bloom (1987) occasionally found it was difficult or
time consuming to capture both sexes of Northern Gos-
hawks (A. gentilis). Females were usually caught within 15
min, but males were often not captured. He speculated
that the male is less aggressive toward the owl during the
post-fledging period or is away from the nest (hunting)
and is unaware of the owl’s presence. With Sharp-
shinned Hawks and American Kestrels, we found of the
birds that were present (assumed to have seen the owl),
females responded more aggressively toward the owl
mount than did males. Trapping success for female
Sharp-shinned Hawks and female American Kestrels were
91% (21 of 23) and 79% (11 of 14), respectively. Males
of both species occasionally showed a reluctance to
“stoop” at the owl, resulting in a trapping success of 68%(13 of 19) for male Sharp-shinned Hawks and 63% (10
of 16) for male American Kestrels. The escape rate (per-
centage of birds that hit the dho-gaza net, but were not
captured) was 1.8% (2 of 113).
Benefits of this technique include: (1) a high response
rate; (2) a low escape rate; (3) the ability to readily adjust
net height; (4) minimal space (especially when com-
pared to a 12-m mist net) is required for setup; (5) this
technique kept the net off the ground, and hence, re-
quired less preparation time to reset the net after a cap-
ture when compared to a ground-level dho-gaza net.
Albanese and Piaskowski (1999) and Stokes et al.
(2000) have described similar techniques that use elevat-
ed mist nets to study birds that spend the majority of
their time in woodland canopies. However, those studies
used conventional mist nets in a manner designed for
continuous use at one location. Our technique was de-
signed to capture specific birds near their nest sites with
a mobile apparatus that allows researchers to visit multi-
ple locations with a minimal amount of setup time (ca.
15 min).
Even though we conducted 113 captures without any
visible injury, there is the potential for serious injury to
species that “stoop” at higher speeds and are of greater
mass than the Red-shouldered Hawk. A net that com-
pletely releases from the uprights (Bloom 1987) as well
as other modifications may be necessary to accommodate
the force of a larger raptor hitting the net. Alternatively,
because the “cut-down” mist net was successful in cap-
turing Ferruginous Pygmy-Owls as they approached or
exited the entrance to their nest cavity, this technique
should be effective for trapping most small cavity-nesting
birds without modification.
Resumen.—Debido a su alta tasa de exito, el uso de una
red de niebla en combinacion con un senuelo de Bubo
virginianus, es una de las tecnicas populaces mas usadas
para capturar rapaces durante su anidacion. Sin embar-
go, el protocolo estandar para esta tecnica limita su efec-
tividad a aves que tiene la habilidad de volar cerca al nivel
del suelo (<3 m) para atropellar al senuelo. Con el fin
de proveer una tecnica alternativa que pueda mejorar la
tasa de captura en algunas situaciones, construimos yprobamos un ensamblaje de redes elevado consistente de
un poste telescopico de aluminio, una barra cruzada hor-
izontal, dos postes verticales rectos, una red de niebla, yun buho raecanico. Desde 1994-2001, el exito en la cap-
tura de cinco especies de rapaces de talla pequena a me-
diana fue 73% (113/154 intentos). Debido a su adapta-
bilidad, el alto exito de captura y el bajo costo, este
sistema puede ser una herramienta beneficiosa para la
investigadon de las aves.
[Traduccion de Cesar Marquez]
Acknowledgments
We thank D. Haessly and R. Rosenfield for providing
information on the effectiveness of our system on Amer-ican Kestrels and Cooper’s Hawks, respectively. J. Runke
December 2002 Short Communications 323
provided the drawing in Figure 1. J. Bielefeldt, P. Bloom,
J Marks, M. McMillian, and B. Woodbridge provided
helpful suggestions for improving this manuscript.
Literature Cited
Albanese, G. and V.D. Piaskowski. 1999. An inexpensive
elevated mist net apparatus. N. Am. Bird Bander 24:
129-134.
Bloom, P.H. 1987. Capturing and handling raptors. Pag-
es 99-123 in B.A. Millsap, K.W. Cline, B.G. Pendleton,
and D.A. Bird [Eds.],Raptor management techniques
manual. Natl. Wildl. Fed., Washington, DC U.S.A
, J.L. Henckel, E.H. Henckel, J.K. Schmutz, B.
Woodbridge, J.R. Bryan, R.L. Anderson, P.J. De-
TRicH, T.L. Maechtke, J.O. McKinley, M.D. McCrary,
K. Titus, and P.F. Schempf. 1992. The dho-gaza with
Great Horned Owl lure: an analysis of its effectiveness
in capturing raptors./. Raptor Res. 26:167—178.
Clark, W.S. 1981. A modified dho-gaza trap for use at a
raptor banding station. J. Wildl. Manage. 45:1043-
1044.
and B.K. Wheeler. 1987. A field guide to hawks
in North America. Houghton Mifflin Co., Boston, MAU.S.A.
Card, N.W., D.M. Bird, R. Densmore, and M. Hamel1989. Responses of breeding American Kestrels to live
and mounted Great Horned Owls. J. Raptor Res. 23
99-102.
Hamerstrom, F. 1963. The use of Great Horned Owls in
catching marsh hawks. Proc. XIII Int. Ornithol. Congr
13:866-869.
Jacobs, E.A. 1996. A mechanical owl as a trapping lure
for raptors. / Raptor Res. 30:31-32.
McCloskey, J.T. and S.R. Dewey. 1999. Improving the
success of a mounted Great Horned Owl lure for trap-
ping Northern Goshawks./. Raptor Res. 33:168-169
Roseneield, R.N. and j. Bielefeldt. 1993. Trapping tech-
niques for breeding Cooper’s Hawks; two modifica-
tions. /. Raptor Res. 27:171-172.
Steenhof, K., G.P. Carpenter, and J.C. Bednarz. 1994
Use of mist nets and a live Great Horned Owl to cap-
ture breeding American Kestrels. J. Raptor Res. 28.
194-196.
Stokes, A.E., B.B. Schultz, R.M. Degraaf, and C.R
Griffin. 2000. Setting mist nets from platforms in the
forest./. Field Ornithol. 71:57-65.
Received 31 December 2001; accepted 13 July 2002
J Raptor Res. 36(4):324-327
© 2002 The Raptor Research Foundation, Inc.
Florida Bald Eagle (Haliaeetus leucocephalus) Egg Characteristics
M. Alan Jenkins, 1 Steve K. Sherrod, David A. Wiedenfeld, and Donald H. Wolfe, Jr.
George Miksch Sutton Avian Research Center, RO. Box 2007, Bartlesville, OK 74005 U.S.A.
Key Words: Bald Eagle, Haliaeetus leucocephalus; eggs\
eggshell characteristics', pesticides.
The Bald Eagle {Haliaeetus leucocephalus)
,
south of the
40th parallel, was declared endangered by the U.S. Fish
and Wildlife Service in 1967 owing to an observed pop-
ulation decline in the 48 contiguous states, which was
hrst noticed in Florida. A population of eagles in western
peninsular Florida showed a sharp decline by 1957-58
(Broley 1958), and in eastern-central Florida the species
declined by two-thirds between 1951-61 (Howell 1963).
Those declines were later attributed to poisoning or the
weakening effects on eggshells caused by chlorinated hy-
drocarbon pesticide residues, notably DDE (Nisbet
1989). Eggs with shells thinned by DDE broke before
hatching, destroying the egg and resulting in lowered
productivity. From 1984—91 biologists with the George
Miksch Sutton Avian Research Center collected entire
clutches of Bald Eagle eggs from Florida nests as part of
a project to restore nesting populations of this species to
the southeastern U.S. (Sherrod et al. 1989). The eggs
were incubated and hatchlings were reared in Oklahoma,
and the young were released by hacking in eight south-
eastern states. This paper describes the physical charac-
teristics of 395 Bald Eagle eggs and the analysis of pesti-
cide residues in 15 unhatched eggs collected during that
project. We report the results of testing for correlations
between egg characteristics, location of collection, year,
sex of the eagle hatched, and information on organo-
chlorine pesticides and eggshell thickness.
Study Area and Methods
Eggs were collected from nine counties in north-cen-
tral Florida (Fig. 1). At collection, each egg was markedwith a unique number, measured for length and breadth
with a caliper to the nearest 0.01 mm, and weighed to
the nearest 0.1 g (balance) or 0.01 g (electronic scale).
After incubation, the shells of hatched eggs were air-
dned and their thickness measured. Unhatched eggs
were frozen for as long as a year, a method of preserva-
tion which does not change the level of pesticide con-
centrations even if thawing and microbial degradation
occur (Stickel et al. 1984). Unhatched eggs were opened,
the contents removed, the shells were air-dried, and the
shell thickness measured.
Thickness measurements were made on fragments of
shell from three evenly spaced places near the equator.
Fragments were clamped in a hemostat and viewed with
a binocular microscope at lOOX. One microscope eye-
1 E-mail address: [email protected]
piece was equipped with a micrometer calibrated with a
stage micrometer. Each shell sample was viewed with the
microscope on its edge, the number of calibrations span-
ning the fragment recorded, and the thickness calculated
using a constant conversion factor obtained from the cal-
ibration (Enderson et al. 1982). The three thickness mea-surements of each egg were averaged.
Shell membranes of hatched eggs usually shrank, be-
coming detached from the shell and so they could not
be measured as part of the shell’s thickness. Shell mem-branes from unhatched eggs sometimes remained at-
tached after drying and, where possible, shells were mea-sured with attached membranes, then the membranesremoved and shell thickness re-measured. This gave shell
thicknesses with and without membranes for 37 eggs.
This allowed us to correct for loss of shell thickness
caused when shell membranes become detached. De-
tachment of the shell membranes after drying slightly
reduces the measured total shell thickness because the
mammillary tips from the shell come away attached to
the outer shell membrane during detachment (Terepka
1963).
Calculated egg volumes presented here include the
shell volume, a method preferable to trying to determine
inside volume (Stickel et al. 1973). The calculated vol-
ume formula was determined to be within —8 to +7 per-
cent of measured volumes for this species (Stickel et al
1973). Shell thicknesses may decrease during embryo de-
velopment as the embryo uses calcium from the shell for
bone formation (Romanoff and Romanoff 1949). How-ever, most of the decrease apparently occurs in the mam-millae core (Bond et al. 1988) and does not contribute
significantly to shell thinning (Bunck et al. 1985). Cal-
culated egg volume (V) was estimated using the formula
V = 0.508LB^ (Stickel et al. 1973), where L = length of
egg (cm) and B = breadth of egg (cm) . Calculated fresh
egg mass (M) was estimated as M = 0.56227LB^. Thecoefficient of 0.56227 yielded the best estimate of hatch-
ing date, assuming a period from the beginning of in-
cubation to pip of 33.5 d.
Unhatched eggs were considered fertile if they showedany sign of embryonic development upon dissection
Hatch order within clutches was recorded based on pip-
ping date and time. Hatch order was assumed to be iden-
tical with laying order because female eagles lay eggs a
few days apart and begin incubation with the first eggs,
making hatching within a clutch asynchronous (Gerrard
and Bortolotti 1988). However, time of pipping was only
accurate within ca. 12 hr because eggs were checked
twice daily for pipping.
Sex of fledgling-age eagles was determined from mea-
surements of bill depth and toepad length following the
methods of Walborn (1991).
Egg length, breadth, volume, length/breadth ratio, cal-
culated fresh mass, and shell thickness were checked for
324
December 2002 Short Communications 325
Key to Counties
A = Alachua O = Osceola
H = Highlands Po = Polk
La = Lake Pu = PutnamLe = Levy S - Seminole
M = Marion V = Volusia
Figure 1. Florida Bald Eagle study area and counties of egg collections.
correlations with year and the latitude of the Florida
county where collected to determine any latitude trend.
Analysis of variance was used to compare shell thickness,
volume, and hatch order by sex; volume and shell thick-
ness (for all and for both sexes) by hatch order; andvolume and shell thickness with fertility. Statistical tests
were made using Systat statistical package, version 7.0.
Organochlorine and polychlorinated biphenyl pesti-
cide residues of the contents of 15 unhatched eggs wereanalyzed by Hazleton Labs using Food and Drug Admin-istration (1973) methods. The reported residues are
based on calculated fresh egg masses.
Results
No significant correlations were found between egg
length, breadth, volume, length/breadth ratio, calculat-
ed fresh mass, and shell thickness and the year of collec-
tion or the latitude of the Florida county where collected
(Table 1). There was a significant increase of eggshell
thickness from 1984-91 (T - 0.073, df = 392, P < 0.05)
However, the increase was not signihcant if data for 1984
were excluded. The 1984 sample size {N = 18) is biased
by the inclusion of an unusually thin-shelled two-egg
clutch with very high pesticide residues. One of these two
eggs was found broken in the nest; the other failed to
develop. The eggshells we collected were 4.5% thinner
than the pre-1947 Florida sample {N = 211) measured
by Anderson and Hickey (1972).
Residue analysis results for 23 chlorinated hydrocar-
bons, percent moisture and percent lipids for 15 un-
Table 1 . Summary of Florida Bald Eagle egg characteristics.
Length(L)
(mm)
Breadth
(B)
(mm)
Calculated
Volume(mm^) L/B Ratio
Calcuiated
Fresh Mass
(g)
Shell
Thickness
WithoutMembranes
(mm)
N 392 392 392 392 392 395
Minimum 64.38 48.34 82.30 1.166 90.92 0.312
Maximum 79.50 59.88 140.20 1.517 154.92 0.553
Mean 71.04 55.37 111.08 1.284 122.71 0.453
Standard Deviation 2.732 1.690 9.233 0.051 10.20 0.035
326 Short Communications VoL. 36, No. 4
Table 2. Summary of chlorinated hydrocarbon pesti-
cide residues in 15 unhatched Florida Bald Eagle eggs,
1984-91. Data are corrected to calculated fresh egg mass-
es
Mean(ppm)
Maxi-
mum(ppm)
Mini-
mum(ppm)
Stan-
dard
Devia-
tion
DDE 2.47 10.10 0.66 2.35
DDD 0.05 0.58 0.0 0.14
DDT 0.24 3.89 0.0 0.94
HCB ND*Alpha-BHC NDGamma-BHC (lindane) NDBeta-BHC NDHeptachlor NDAldrin NDOctachlorostyrene NDHeptachlor epoxide 0.01 0.07 0.00 0.02
Oxychlordane 0.06 0.26 0.00 0.06
Gamma-chlordane 0.04 0.15 0.00 0.04
Alpha-chlordane NDTransnonachlor 0.29 1.06 0.00 0.25
Mirex NDDieldrin 0.10 0.66 0.00 0.15
Endrin NDMethoxychlor NDToxaphene NDPCB 1260 5.13 15.47 0.00 5.50
PCB 1248 0.02 0.24 0.00 0.06
PCB 1254 5.82 28.15 0.00 8.03
Percent moisture 80.78 83.60 76.00 2.04
Percent lipids 5.15 12.00 2.20 2.19
ND = None detected above detection limit of 0.1 ppm or lower.
hatched eggs are presented in Table 2 as benchmark data
for possible future information on this population.
Discussion
Bald Eagle body size is known to increase with increas-
ing latitude (Stalmaster 1987), but we found no correla-
tion of egg size characteristics with the small latitude span
we sampled. We speculated that eggs laid later in a clutch
might be smaller than the first, but our data failed to
detect such a trend. Likewise, sex of the eagles hatched
did not correlate with size of the egg or hatch order.
We expected an increase in eggshell thicknesses and
lessening of chlorinated hydrocarbon residues during the
years of our study because most uses ofDDT in the U.S.A.
have been banned; however, our thickness data did not
show a change over time during the period of our study.
The residues for our eggs, except one egg with high DDEresidues, are below the threshold levels indicated by
some authors as sufficient to affect raptor productivity
(Fyfe et al. 1988, Nisbet 1989, Risebrough 1989). Meanproductivity of Florida Bald Eagles during the years of
egg collection was 1.10 young/occupied territory (Nes-
bitt et al. 1998), and above the minimum of 1.0 young/
occupied territory that Wiemeyer et al. (1993) consid-
ered as representing a healthy population. Based on
these data, we believe that by 1984 the population of nest-
ing Bald Eagles in the areas of Florida from which wecollected eggs were reproducing at a rate that met the
criteria suggested by Wiemeyer et al. (1993). This pop-
ulation was relatively free of pesticide contamination and
that eggshell thinning was no longer a problem.
Resumen.—Las medidas y calculos de las medidas de 395
huevos de aguilas calvas {Haliaeetus leucocephalus) colec-
tados en Florida desde 1985-91 fueron evaluadas por me-
dio de relacion estadistica para el ano de coleccion, la-
titud del condado donde fueron colectados, sexo del
polluelo y orden de salida del huevo. No se encontraron
correlaciones significantes. Se hicieron analisis de resi-
duos de pesticidas organoclorados y bifenil policlorina-
dos en 15 huevos sin empollar. Con excepcion de una
nidada, los residues organoclorados fueron bajos.
[Traduccion de Cesar Marquez]
Acknowledgments
Cooperation for this project was given by the Florida
Game and Fresh Water Fish Commission, in particular
Don Woods and Steve Nesbitt; The University of Florida,
especially Michael Collopy, Petra Bohall Wood, and Rob-
ert Rosen; and the U.S. Fish and Wildlife Service’s En-
dangered Species Program and Regions 2 and 4. Grateful
thanks are due to our numerous funders and the Sutton
Board of Directors. Many Sutton employees worked tire-
lessly to make the restoration project successful, Alan Be-
ske, Gwyn McKee, and Sheryl Tatora in particular. JamesEnderson loaned eggshell measuring equipment. Themanuscript was greatly improved by comments fromStanley N. Wiemeyer, James C. Bednarz, Sally Jenkins,
and two anonymous reviewers.
Literature Cited
Anderson, D.W. and J.J. Hickey. 1972. Eggshell changes
in certain North American birds. Pages 514-540 in
K.H. Voous [Ed.], Proc. XV Int. Ornithol. Congr. Leiden,
Germany.
Bond, G.M., R.G. Board, and V.D. Scott. 1988. A com-
parative study of changes in the fine structure of avian
eggshells during incubation. Zool.J Linn. Soc. 92:105-
113.
Broley, C.L. 1958. The plight of the American Bald Ea-
gle. Audubon 60:162-163, 171.
Bunck, M.M., J.W. Spann, O.H. Patee, and W.J. Fleming
1985. Changes in eggshell thickness during incuba-
tion: implications of evaluating the impact of organ-
ochlorine contaminants on productivity. Bull. Environ
Contam. Toxicol. 35:173-182.
Enderson, J.H., G.R. Craig, W.A. Burnham, and D.D.
December 2002 Short Communications 32V
Berger. 1982. Eggshell thinning and organochlorine
residues in Rocky Mountain peregrines, Falco peregti-
nus, and their prey. Can. Field-Nat. 96:255-264.
Food and Drug Administration. 1973. Pesticide analyt-
ical manual. Vol. 1, Washington, DC U.S.A.
Fyfe, R.W., R.W. Risebrough, J.G. Monk, W.M. Jarman,
D.W. Anderson, L.F. Kief, J.L. Linger, I.C.T. Nisbet,
W. Walker, II, and BJ. Walton. 1988. DDE, produc-
tivity, and eggshell thickness relationships in the ge-
nus Falco. Pages 319—335 in T.J. Cade, J.H. Enderson,
C.G. Thelander, and C.M. White [Eds.], Peregrine
Falcon populations: their management and recovery.
The Peregrine Fund, Boise, ID U.S.A.
Gerrard, J.M, and G.R. Bortolotti. 1988. The Bald Ea-
gle. Smithsonian Institution, Washington, DC U.S.A.
Howell, J.C. 1963. The 1961 census of some Bald Eagle
nests in east-central Florida. Auk 79:716-718.
Nesbitt, S.A., M.A. Jenkins, S.K. Sherrod, D.A. Wood,A. Beske, J.H. White, P.A. Schulz, and S.T. Schwik-
ert. 1998. Recent status of Florida’s Bald Eagle pop-
ulation and its role in eagle reestablishment efforts in
the southeastern United States. Proc. Annu. Conf.
Southeast. A.ssoc. Fish Wildl. Agencies 52:377-383.
Nisbet, I.C.T. 1989. Organochlorines, reproductive im-
pairment, and declines in Bald Eagle (Haliaeetus leu-
cocephalus) populations: mechanisms and dose-re-
sponse relationships. Pages 483-489 in B.-U. Meyburg
and R.D. Chancellor [Eds.], Raptors in the modernworld. WWGBP, Berlin, Germany.
Risebrough, R.W. 1989. Toxic chemicals and birds of
prey: discussion at Eilat in 1987. Pages 515-525 in
B.-U. Meyburg and R.D. Chancellor [Eds.], Raptors
in the modern world. WWGBP, Berlin, Germany.
Romanoff, A.L. and AJ. Romanoff. 1949. The avian egg.
John Wiley and Sons, Inc., New York, NY U.S.A.
Sherrod, S.K., M.A. Jenkins, G. McKee, D.H. Wolfe, Jr ,
and S. Tatom. 1989. Restoring nesting Bald Eagle
Haliaeetus leucocephalus populations to the southeast-
ern United States. Pages 353-357 in B.-U. Meyburgand R.D. Chancellor [Eds.], Raptors in the modernworld. WWGBP, Berlin, Germany.
Stalmaster, M.V. 1987. The Bald Eagle. Universe Books,
New York, NY, U.S.A.
Stickel, L.F., S.N. Wiemeyer, and LJ. Blus. 1973. Pesti-
cide residues in eggs of wild birds: adjustment for loss
of moisture and lipid. Bull. Environ. Contam. Toxicol 9
193-196.
Stickel, W.H., L.F. Stickel, R.A. Dyrland, and D.H.
Hughes. 1984. Comparison of methods of preserving
tissues for pesticide analysis. Environ. Monit. Assess. 4-
113-118.
Terepka, A.R. 1963. Organic-inorganic interrelationships
in avian egg shell. Exp. Cell Res. 30:183-192.
Walborn, E.B. 1991. Use of morphometric measure-
ments in determining sex of southern Bald Eagles.
M.S. thesis, Oklahoma State University, Stillwater, OKU.S.A.
Wiemeyer, S.N., C.M. Bunck, and C.J. Stafford. 1993.
Environmental contaminants in Bald Eagle eggs
(1980-1984) and further interpretations of relation-
ships to productivity and shell thickness. Arch. Environ.
Contam. Toxicol. 24:213—227.
Received 7 January 2002; accepted 25 July 2002
J Raptor Res. 36(4):328-331
© 2002 The Raptor Research Foundation, Inc.
Osprey Ecology in the Mangroves of Southeastern Brazil
Robson Silva e Silva^
Rua Sdo Jose 48/31, 11040-200, Santos, SP, Brazil
Fabio OlmosLargo do Paissandu 100/4C, 01034-010, Sdo Paulo, SP, Brazil
Key Words: Osprey; Pandion haliaetus; Brazil; diet; man-
grove, wintering ecology.
The Osprey {Pandion haliaetus) is a widely distributed
raptor found in every continent but Antarctica. The Eur-
asian nominate and North American subspecies {P. h. car-
ohnensis) make extensive migrations, the latter being a
trans-equatorial migrant wintering in United States (Flor-
ida), Mexico, Central America and South America from
Colombia to Argentina and Chile (Poole 1989, del Hoyoet al. 1994, Martell et al. 2001).
In Brazil, Ospreys have been recorded in almost every
state and month, but most records were made between
September and April (Sick 1997). The Amazon basin,
where reports are most common, seems to be the main
wintering area for Ospreys in the country, but there are
also clusters of records in coastal localities (Sick 1997,
Olmos and Silva e Silva 2001). Band recoveries made in
Brazil show the birds come from the Mid-Atlantic and
northeastern USA (Poole and Agler 1987).
Despite being a well-known species in its breeding
grounds (del Hoyo et al. 1994), there is little information
on the wintering ecology of Ospreys in South America
(Saggese et al. 1996), although detailed studies have
been made in Africa (Prevost 1982, Boshoff and Palmer
1983). Ospreys spend most of the year (six or moremonths) in their wintering grounds, so information on
their ecology during this period is critical for a clearer
understanding of their life-histories and the pressures
laced by the birds outside the breeding season. Here, we
provide an account of the ecology of Ospreys using a
mangrove eco.system in southeastern Brazil, the first such
study in South America.
SruDY Area AND Methods
The study was conducted in the mangrove ecosystem
that covers the estuarine area between Sao Vicente Island
and the mainland, in the coast of Sao Paulo state, south-
eastern Brazil (ca. 23°53'S, 46°23'W). This area, belong-
ing to the Santos and Cubatao counties, is part of the
major mangrove ecosystem located in the region knownas Baixada Santista, covering 120 km^, and located in oneof the most populated and developed areas in Brazil
(Lamparelli 1999). The local climate is hot and humid,with annual rainfall ranging from 2000 to over 2500 mm.
^ E-mail address: [email protected]
Winter is the driest season, the lowest rainfall occurring
in July-August, the highest values occurring between Sep-
tember-March (Olmos and Silva e Silva 2001). For a gen-
eral description of the area’s geography and environ-
ment, see CETESB (1991) and Olmos and Silva e Silva
(2001 ).
The main feature in the study area is a channel (Pia-
gaguera channel) bisecting it and connecting Santos Bayto the estuarine area inland. This broad (ca. 1 km wide)
channel is mostly man-made and regularly dredged to
allow for the passage of cargo ships serving the local steel
and fertilizer plants. Because of dredging and silting,
there are large mudflats along the channel. Ten naviga-
tion buoys and six concrete towers dot the entire length
of the channel and are used as perches by feeding Os-
preys. Prey remains accumulate on top of these buoysand towers, making collecting the collection of dietary
data simple. Three rivers (Quilombo, Casqueiro, and Cu-
batao) empty into the channel.
Diet and behavioral data were collected as part of a
broader study of the mangrove avifauna conducted fromMarch 199T-July 2000 during 231 field-days (Olmos andSilva e Silva 2001). Data on Osprey abundance through-
out the year and habitat use were gathered between Au-gust 1995-November 1996, when we made 36 standard-
ized bird censuses by boat along a 19.25 km transect
covering all habitats present (Olmos and Silva e Silva
2001 ).
Habitat classification was adapted from the mappingmade by Sao Paulo state’s environmental agency (CE-
TESB 1991) and represents a gradient of mangrove tree
cover. Habitat categories sampled were: mangrove forest
with mostly touching canopies and complete cover, de-
graded mangrove with many gaps between trees makinga patchwork of clearings, mangrove degraded by pollu-
tion, groups of mangrove trees, and large areas of her-
baceous growth dotted by dwarfed mangroves, a mosaic
of mudflats (with scattered mangrove trees), and ex-
posed mudflats without any tree cover. For a detailed de-
scription of habitats see Olmos and Silva e Silva (2001)
Feeding Ospreys were observed opportunistically with
the help of spotting scopes and binoculars with the aimof identifying the captured prey. Prey remains accumu-lated on buoys and towers were recovered during regular
checks and identified to the lowest possible taxonomiclevel by comparison to reference material.
Results
Ospreys were first recorded along the Piagaguera chan-
nel in 1986 (Olmos 1989). Interestingly, the species was
not found there earlier in the 20th century (Luederwaldt
328
December 2002 Short Communications 329
Figure L Monthly numbers of Ospreys censused in the Santos-Cubatao mangroves, southeastern Brazil, between
August 1995-November 1996.
1919). It is almost impossible to tell adult birds from
young ones under field conditions (Boshoff and Palmer
1983), but we never observed newly-fledged Ospreys,
with their characteristic speckled plumage.
Ospreys are recorded in Santos-Cubatao throughorxt
the year. Census data show a peak during the austral sum-
mer and a minimum of three birds during the winter
(Fig. 1). Most (47%) records made during the censuses
were along the Cascalho River, where channel margins
are dominated by mangroves degraded by pollution (Ol-
mos and Silva e Silva 2001).
Table 1. Prey items of wintering Ospreys in the man-
groves of Santos and Cubatao, Brazil. Unidentified fish
were excluded.
Species N Percent
Mullets
Mugil sp. 69 76.7
Rhomboid mojarra
Diapterus rhombeus 16 17.8
Snooks
Centropomus sp. 2 2.2
Common trahita
Hoplias malabaricus 1 1.1
Brazilian mojarra
Eugerres brasilianus 1 1.1
Brazil geophagus
Geophagus brasiliensis 1 1,9
Total 90 100
From year-round census data. Ospreys had higher lin-
ear densities along rivers bordered by mangrove forest (x
= 0.71 birds/km) and mangroves degraded by pollution
(0.70 birds/km) compared to mudflats (0.2 birds/km)
and degraded mangrove (0.01 birds/km, Fij440 = 14 09,
P < 0.0001). Densities in mangrove forest and mangrove
degraded by pollution were not different, as well as dif-
ferences in densities between mudflats and degraded
mangroves (Tukey HSD test, both P < 0.001).
Most fish seem to be captured alive, but in November
1996, we did record an Osprey taking a dead fish floating
on the surface. The most important prey were mullets
(Mugil spp.) (76.7%) and rhomboid mojarra {Diapterus
rhomheus) (17.8%; Table 1). Only two freshwater fish,
common trahita {Hoplias malabaricus) and Brazil geopha-
gus {Geophagus brasiliensis) were recorded. One mullet
{Mugil platanus) left whole on a tower was 41. .5 cm TLand weighed 590 g, while a Diapterus rhombeus found mthe same circumstances was 30 cm and 490 g. Based on
prey remains and observations, fish smaller than 20 cmTL seem to be rare in the diet of Ospreys in southeastern
Brazil.
We rarely observed Ospreys hovering or flying low over
the water before capturing a fish. Once, an Osprey
caught a dying fish on the surface while “hovering.” In
most instances, the birds would soar over the water and
plunge dive rapidly after locating a fish. It was commonfor the birds to abort several dives (up to nine in a row)
before actually touching the water.
Ten out of 14 plunge dives by different birds were suc-
cessful (71%), with nine fish carried away and one falling
back to the water. After taking a fish, the birds would fly
330 Short Communications VoL. 36, No. 4
to one of the available towers, buoys, trees, or when the
prey was too heavy, even a mudflat. All hsh were eaten
head first, discarding opercula and gills. Mullet viscera
were also discarded. Usually only the tail would remain
but, sometimes, we would find the posterior half of a
large mullet. After feeding, the bird would fly dragging
its feet in the water for over TO m. Sometimes up to three
birds were seen fishing in the same small area. When one
was successful the others would chase it amid much call-
ing, trying to steal its fish.
A curious behavior was observed on 22 August 1997,
at the Pia^aguera channel. One Osprey, while holding a
tree branch, was seen flying and calling after another in-
dividual. The second bird would perch, also calling. Thefirst bird flew out of sight but came back quickly, always
calling, without the branch. Both birds then began to
soar, always calling, making several aborted dives. After
one Osprey finally captured an unidentified fish, it flew
away being followed by the other bird. An Osprey flying
while holding a tree branch was also seen on 18 July
2000; this bird was chasing a Crested Caracara (Polyborus
plancus),but we soon lost sight of them.
Contrary to the behavior reported in some wintering
areas (Boshoff and Palmer 1983), Ospreys were very vo-
cal in Santos-Cubatao throughout the year, especially
when two birds came close to each other. It was commonto see two Ospreys soaring together with Black Vultures
( Coragyps atratus) while calling. They would also call whenwe approached the perch of a feeding bird, which caused
It to fly with its prey.
Yellow-headed Caracaras {Milvago chimachima) benefit
from Ospreys by scavenging fish remains from the feed-
ing perches, sometimes waiting beside a feeding Osprey.
Crested Caracaras are more aggressive and actively try to
steal fish from the Ospreys; sometimes up to four cara-
caras may join in a chase after an Osprey carrying a fish,
but we never saw them being successful. Interestingly,
Great Egrets {Casmerodius alhus) would expel Ospreys
Irom their feeding perches, while Kelp Gulls {Larus dom-
imcanus), known to steal Ospreys’ food in South Al'rica
(Boshoff and Palmer 1983), ignore them in Brazil.
Ospreys did not seem to be actively persecuted by local
people and the many fishermen using the mangroves.
Nevertheless, on 26 December 1996, a female was found
with a wounded wing, perhaps the result of being shot.
This bird is now in the ornithological collection of the
Museu de Zoologia da Universidade de Sao Paulo
(MZUSP 74346).
Discussion
The lack of records of newly-fledged Ospreys with their
characteristic speckled plumage suggests only birds over
1 yr-old migrate to the study area. The year-round pres-
ence of Osprey in Brazil raises the possibility the birds
might breed in South America, but no evidence has been
found so far (Sick 1997). Nevertheless, nesting in a win-
tering area has been documented in South Africa (Dean
and Tarboton 1983). The presence of Ospreys in Brazil
during April-August show non-breeders, juveniles, stay in
their wintering range.
Although Sick (1997) attested, without details, that Os-
preys sometimes take mammals and birds when winter-
ing, the only documented food items of Ospreys in Brazil
were fish, making the diet seem less diverse compared to
breeding areas (Wiley and Lohrer 1973). Mullets are de-
tritus-eating fish abundant in Brazilian estuaries, where
they gather in shoals year-round (Menezes 1983). Their
abundance, size, and the habit of sunning close to the
surface make them ideal prey for a plunge diver like the
Osprey. In fact, the only former report of a prey taken
by an Osprey in Brazil refers to a mullet (Mugil incilis)
(Martuscelli 1992), also taken in a mangrove area in
southern Sao Paulo state. Mullet was also the main prey
taken by wintering Ospreys in mangroves and estuaries
in Senegal (Prevost 1982) and South Africa (Boshoff and
Palmer 1983). The availability of mullet may probably ex-
plain why Ospreys seem to be the most common in coast-
al areas, especially estuaries and mangroves (Haver-
schmidt and Mees 1994). Fish were also the only prey
recorded as taken by Ospreys in freshwater habitats in
Peru (Willard 1985) and Argentina (Saggese et al. 1996),
the detritus-eating Prochilodus sp. being reported by both
studies. We observed a high capture success (71%) for a
limited number of foraging attempts on fish, but not out-
side the 40-70% range reported by studies elsewhere
(Poole 1989, del Hoyo et al. 1994).
There is no direct or intensive persecution of Ospreys
in southeast Brazil. Nevertheless, their reliance on detri-
tus-eating fish might be problematical. The Santos-Cu-
batao estuary receives the discharges of one of the major
industrial areas in Brazil, well-known in the 1980s for its
high pollution levels (Gutberlet 1996). Despite improve-
ments, the sediments still hold high levels of heavy metals
and organochlorines such as Hexachlorobenzene (HCB)
and Polycyclic aromatic hydrocarbons (PAHs). For ex-
ample, sediments from the Piagaguera channel hold
109.200 to 733.700 [xg/kg of benzopyrene, some of the
largest concentrations in the world (CETESB 2001).
These contaminants may be ingested by fish like mullet,
feeding on detritus and benthic algae, and accumulated
and transferred to piscivores like Ospreys. Thankfully,
most contaminants seem to be trapped in the sediment
and mullet samples generally have small concentrations
(CETESB 2001), although this situation may change if
dredging makes the compounds available again in the
water column.
RF..SUMEN.—Las aguilas pescadoras {Pandion haliaetus) son
registradas todo el ano en los manglares de Santos-Cu-
batao al suroriente del Brasil, con un pico de abundancia
entre diciembre y marzo. Las aves usan todos los habitat
del manglar pero las densidades lineares mas altas ocur-
ren a lo largo de rios bordeados por bosques de manglar
{x = 0.71 aves/km) y manglares degradados por polu-
December 2002 Short Communications 331
cion (x = 0.70 aves/km). Las ^uilas pescadoras fueron
registradas comiendo unicanaente pescado y mostraron
una alta tasa de exito (71% de los intentos). Los salmo-
netes {Mugil spp.) fueron el item de comida mas comun(77%), seguido por las mojarras romboides {Diapterus
rhombeus) (18%). A pesar de la historia de alta polucion
industrial del area, los niveles de contaminantes en las
especies presa consumidos por el aguila pescadora fu-
eron bajos, y la especie no fue perseguida por los pob-
ladores locales.
[Traduccion de Cesar Marquez]
ACKNOWr.EDGMENTS
This work was possible through grants received fromFunda^ao O Boticario de Protegao a Natureza, MacAr-thur Foundation and Ultrafertil S.A. to both authors. Weare very grateful for their timely support over the years.
We also thank Maria do Carmo Amaral (Cubatao Zoo,
Cotia-Para Ecological Park) for saving the Osprey speci-
men now in the MZUSP. Joel Escobar and the personnel
at Nautica da Ilha provided invaluable support when weneeded to deal with boats and outboard motors. We wish
to thank Mark Martell, Alan E. Poole, and Richard O.
Bierregaard, Jr. for comments and suggestions on im-
proving the manuscript.
Lu erature Cited
Boshoff, A.E. and N.G. Palmer. 1983. Aspects of the bi-
ology and ecology of the osprey in the Cape Province,
South Africa. Ostrich 54:189-204.
Companhia Estadual de Tecnologia e Saneamento Am-
biental. 1991. Avaliayao do estado de degradagao dos
ecossistemas da Baixada Santista. Sao Paulo, Brazil.
. 2001. Levantamento da contaminagao ambiental
do sistema estuarino Santos/Sao Vicente. CETESB,
Sao Paulo, Brazil.
Dean, W.R.J. and W.R. Tarboton. 1983. Ospreys breed-
ing records in South Africa. Ostrich 54:238-239.
Gutberlet,J. 1996. Cubatao: desenvolvimento, exclusao
social, degrada^ao ambiental. Edusp/Fapesp, Sao
Paulo, Brazil.
del FIoyo, J., a. Elliott, and J. Sargatal (Eds.). 1994.
Handbook of the birds of the world. Vol. 2. New world
vultures to guineafowl. Lynx Edicions, Barcelona,
Spain.
Haverschmidt, E. and G.F. Mees. 1994. Birds of Surina-
me. Vaco Press, Paramaribo, Suriname.
IuAMPARELLI, C.C. 1999. Mapeamento dos ecossistemas
costeiros do estado de Sao Paulo. Secretaria do MeioAmbiente/CETESB, Sao Paulo, Brazil.
Luederwaldt, H. 1919. Os manguesaes de Santos. Rev
Mus. Paulista 11:310-409.
Martell, M.S., C.H. Henny, RE. Nye, and M.J. Soi.ensky
2001. Fall migration routes, timing, and wintering
sites of North American Ospreys as determined by sat-
ellite telemetry. Condor 103:715-724.
Martuscelli, P. 1992. Notas sobre aves pouco conheci-
das do estado de Sao Paulo. Pages 82-83 in Anais do
VI Encontro Nacional de Anilhadores de Aves, EDU-CAT, Pelotas, Brazil.
Menezes, N.A. 1983. Guia pratico para conhecimento e
identificayao das tainhas e paratis (Pisces, Mugilidae)
do litoral Brasileiro. Rev. Brasil. Zool. 2:1-12.
Olmos, E. 1989. A avifauna da baixada do polo industrial
de Cubatao. Rev. Bras. Biol. 49:373-379.
and R. Silva e Silva. 2001. The avifauna of a
southeastern Brazilian mangrove swamp. Int. J. Orm-
thol. 4:137-207.
Poole, A.F. 1989. Ospreys: a natural and unnatural his-
tory. Cambridge Univ. Press, Cambridge, U.K.
AND B. Agler. 1987. Recoveries of Ospreys band-
ed in the United States, 1914-84. y. Wildl. Manage. 51.
148-155.
Prevost, Y.A. 1982. The wintering ecology of Ospreys in
Senegambia. Ph.D. dissertation, University of Edin-
burgh, Scotland.
Saggese, M.D., E.R. De Lucca, S.F. Krapovickas, andE.H. Haene. 1996. Presencia del aguila pescadora
{Pandion haliaetus) en Argentina y Uruguay. Hornero
14:44-49.
Sick, H. 1997. Ornitologia Brasileira. Editora Nova Eron-
teira, Rio de Janeiro, Brazil.
Wiley, J.W. and F.E. Lohrer. 1973. Additional records of
non-fish prey taken by Ospreys. Wilson Bull. 85:468-
470.
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twenty-two tropical piscivores. Ornithol. Monogr. 36.
788-797.
Received 8 February 2002; accepted 3 July 2002
/ RapiorRes. 36(4) :332-334
© 2002 The Raptor Research Foundation, Tnc.
Diet of Breeding Tropical Screech-Owls (Otus choliba) in Southeastern Brazil
Jose Carlos MottaJunior'Departamento de Ecologia, Instituto de Biociencias da Universidade de Sdo Paulo, 05508-900, Sdo Paulo, SP, Brazil
Key Words: Tropical Screech-Owl; Otus choliba; breeding
dieL; prey biomass; Brazil.
The Tropical Screech-Owl {Otus choliba) occurs east of
the Andes Mountains from Costa Rica to Uruguay and
northern Argentina, and is also found throughout muchol Brazil (Meyer de Schauensee 1966, Burton 1992, Sick
1993). It is one of the most common and widespread
neotropical owl species inhabiting forest edges, open
woodlands, savannas, and other habitats with some ar-
boreal cover, including urban areas (Sick 1993, del Hoyoet al. 1999). Despite its commonness and widespread dis-
tribution, little ecological information is available on this
species, except for some data concerning natural history
and breeding (Thomas 1977, Smith 1983). Food habits
have been described only qualitatively (e.g., Thomas
1977, Smith 1983, Gallardo and Gallardo 1984). Here, I
provide more detailed information about the diets of
nestling and adult Tropical Screech-Owls during the
breeding season. Data on nest locations and the timing
of reproduction in southeastern Brazil are also present-
ed
Study Area and Methods
The study was conducted at Chacara Mattos/Faber-Cas-
tell (21°59'S, 47°56'W), located 1 km west of the city of
Sao Carlos, Sao Paulo State, Brazil. The 90 ha study area
consists primarily of Pinus spp. plantations with some sec-
ondary-grassland savanna. A small patch (3 ha) of dis-
turbed gallery forest also occurs in this area. The land-
scape surrounding the study area is sugar cane
plantations and the outskirts of the city of Sao Carlos,
fhe climate is a transition between Koppens’s Cwai andAwi, or rainy tropical with a wet (October-March) and a
dry (April-September) season (Tolentino 1967).
Four samples of pellet debris (representing ca. 30 pel-
lets) and six complete pellets were collected from three
occupied nest cavities. This material was washed through
a line mesh screen (0.2 mm) and oven-dried (5(LC) for
24 hr for storage arid analysis. Prey remains were identi-
hed by comparison with a reference collection madefrom material from the study. I also measured the mass
ol prey items collected from the study area. Individuals
m the prey remains were counted by pairing mandibles,
with the exception of beetles and ants, which were count-
ed by the number of heads, and scorpions by the numberof stings. The analyzed prey remains presumably were
from owlets and possibly adults. I also assumed that ver-
tebrate prey were entirely ingested like invertebrates, be-
cause crania and other body bones were always present
' E-mail address: [email protected]
in the pellets. Both prey remains and the reference col-
lection were deposited at the Departamento de Ecologia,
Universidade de Sao Paulo, Brazil.
Results and Discussion
All three nests were in cavities located at a height of
1.0-1. 5 m in dead Eucalyptus sp. tree trunks, presumably
made by woodpeckers originally. Smith (1983) pointed
out that Tropical Screech-Owl nests are typically located
in tree cavities. In spite of the monthly field excursions
to the study area during 1992-93, nests were only found
on 25 November 1992 (Nest 1 ,with one female and three
owlets), 28 October 1993 (Nest 2, with one female and
two owlets), and 6 November 1993 (Nest 3, with one fe-
male and three owlets). The three adult females inside
cavities were captured by hand and weighed with a spring
scale. The mean and standard deviation of body mass was
128.3 ± 11.7 g. Subsequently, the adults were placed back
into the cavities. Prey remains were collected the first
time the nest was found and shortly after owlets fledged.
Analysis of pellets and pellet debris revealed at least 34
species of prey consumed. Invertebrates, mostly orthop-
terans such as Lutosa brasiliensis, were most frequent in
the diet (Table 1). Spiders (Lycosidea) and ants (For-
micidea) were also important numerically. In terms of
biomass, invertebrates also prevail, however, the few ver-
tebrates found, represented a third of the consumed bio-
mass (Table 1).
The mean body mass of prey consumed by Tropical
Screech-Owls was 0.93 ± 2.35 g, ranging from 0.02-28.80
g {N = 309 prey items). Most prey (73.5%) weighed be-
tween 0. 1-1.0 g.
Tropical Screech-Owls only were observed foraging at
night. On two occasions, an individual was observed leav-
ing a perch on a tree and, in flight, capturing insects on
the leaves of another tree. On another occasion, an in-
dividual left a perch on a bush and captured an uniden-
tified invertebrate on the ground. Gallardo and Gallardo
(1984) reported a similar behavior in Tropical Screech-
Owls. 1 have observed these screech-owls catching insects
in flight, particularly in the vicinity of artificial light
sources, which was also reported by Smith (1983) and
Sick (1993). During the period of activity (1800-0600 H)
owls were observed on perches waiting for potential prey;
therefore, this species probably should be classified as a
“sit-and-wait” forager, which is typical for the genus Otus
(Jaksic and Carothers 1985).
The qualitative studies of Thomas (1977) and Smith
(1983) indicated that the diet of Tropical Screech-Owls
consisted mostly of insects in Costa Rica and both insects
332
December 2002 Short Communications 333
Table 1. Prey items found in pellets and pellet debris of Tropical Screech-Owls in southeastern Brazil, with their
percentages in relation to total number and estimated biomass (g). Activity periods and sites of prey were determined
based on field observations and information provided by Manoel M. Dias (pers. comm.).
Prey Items Aciivn Y Period Activity Site
Pfrcfne
NumberPFRt:FNT
Biomass
Rodents
Bolomys lasiurus Nocturnal/crepuscular,
Diurnal
Ground 0.3 10.1
Calomys tener Nocturnal/crepuscular Ground 0.3 3.6
Oligoryzomys nigripes Nocturnal/crepuscular Foliage/branches,
Ground0.3 6.0
Opossums
Gracilinanus sp. Nocturnal/crepuscular Foliage/branches,
Ground0.3 5.7
Snakes
Unidentified small sp. p ? 0.3 3.3
Amphibians
Hylidae (unidentified sp.) Nocturnal/crepuscular Foliage/branches 0.3 5.3
SUBTOTAL VERTEBRATES — — 1.9 34.1
Scorpions
Bothriurus spp. Nocturnal/crepuscular Ground 3.6 1.0
Tityius bahiensis Nocturnal/crepuscnlar Ground 0.3 0.1
Spiders
Lycosidae (unidentified sp.) Nocturnal/crepuscular Ground 11.3 5.9
Unidentified spp. p ? 1.3 0.8
Harvestmen
Opiliones (unidentified sp.) p p 0.3 0.1
Insects
Blattidae {Parahormetica sp.) Nocturnal/crepuscular Ground 1.6 3.2
Blattidae (unidentified sp.) ? ? 0.3 0.2
Termitidae (workers) Nocturnal/crepuscular,
Diurnal
Ground 2.6 0.2
Acrididae spp. Diurnal Foliage/branches 2.9 1.4
Tettigoniidae (Copiphorinae) Nocturnal/crepuscular Foliage/branche s 5.8 6.0
Tettigoniidae (Conocephalinae) Nocturnal/crepuscular Foliage/branches 0.6 0.2
Gryllacrididae {Lutosa brasiliensis) Nocturnal/crepuscular Ground 41.1 34.2
Gryllidae Nocturnal/crepuscular Ground 1.6 1.6
Unidentified Orthoptera ? ? 0.6 0.3
Mantidae Nocturnal/crepuscular Foliage/branches 4.2 2.8
Carabidae (small unidentified spp.) Nocturnal/crepuscular Ground 1.0 0.1
Scarabaeidae (Rutelinae) Nocturnal/crepuscular Foliage/branches 0.3 0.3
Scarabaeidae (Dynastinae) Nocturnal/crepuscular Ground 2.6 3.1
Cerambycidae Nocturnal/crepuscular Tree trunks 1.6 2.4
Unidentified adult Coleoptera ? p 1.0 0 4
Unidentified larvae Coleoptera p ? 1.0 0.4
Lepidoptera (unidentified small moth) ? p 0.3 0 1
Lepidoptera (unidentified caterpillar) ? Foliage/branches 1.0 0 3
Formicidae {Atta sexdens queen) Nocturnal/crepuscular,
Diurnal
Ground 0.3 0.2
Formicidae {Camponotus Nocturnal/crepuscular,
Diurnal
Tree trunks,
Ground5.2 0.1
Formicidae (Dorylinae) Nocturnal/crepuscular,
Diurnal
Ground 1.9 0 1
Formicidae (unidentified spp.) ? p 3.2 0 1
Other unidentified Insecta ? ? 0.3 02
SUBTOTAF INVERTEBRATES — — 98.1 65 9
334 Short Communications VoL. 36, No. 4
and vertebrates in Venezuela, respectively. Prey taken by
these owls include katydids, beetles, cockroaches, small
snakes, and rodents (Thomas 1977, Smith 1983, this
study). Larger species like Otus asio and O. kennicottii
seem to include proportionally more vertebrates in their
diets (e.g., Ritchison and Cavanagh 1992, del Hoyo et al.
1999). On the other hand, smaller species such as O.
tnchopsis, O. flammeolus, and O. choliba appear to be mostly
insectivorous (Ross 1969, del Hoyo et al. 1999, this
study)
.
The frequent consumption of the terrestrial arthro-
pods, Lutosa brasiliensis (Lycosidae) and others (68.5% by
number and 63.3% by biomass) suggests that prey are
often captured on the ground (Table 1). A similar pat-
tern in the prey data supports that the Tropical Screech-
Owls were essentially nocturnal; the diet consists mainly
of night prey (76.8% by number and 81.5% by biomass;
Table 1).
Resumen.—Se estudio la dieta del Autillo Choliba {Otus
choliba) durante el periodo reproductivo, entre los meses
de octubre y diciembre de 1992 y 1993, en nna localidad
del Sudeste de Brasil. Se identificaron por lo menos 34
especies de presas a partir de egagropilas, directamente
colectadas en tres nidos ubicados en cavidades de troncos
muertos a 1.0-1.5 m del suelo. Insectos, en especial Lu-
tosa brasiliensis (Gryllacrididae) y otros ortopteros, arahas
y escorpiones forraaron la base de la dieta. Aunque los
mvertebrados fueron los mas importantes numerica-
mente (98.1% del total de 309 individuos), los vertebra-
dos tuvieron representacion significativa en terminos de
biomasa consumida estimada (34.1% del total de 286.0
g) La inayoria de las presas eran nocturnas y terricolas,
mdicando los habitos de caza de esta lechuza.
[Traduccion del autor]
Acknowledgments
1 thank A.W. Faber-Castell S/A for facilities in the study
site. The entomologists Manoel M. Dias and Alejo M. Lar-
rambebere helped with invertebrate identihcation. Mar-
tha Desmond, F.R. Gehlbach, Gary Ritchison, and Clint
W Boal made valuable comments. Diego Queirolo kindly
revised the Spanish text. This work was a small part of a
Ph.D. dissertation sponsored by Coordenacao De Aper-
feigoamento Ce Pessoal De Nivel Superior and WorldWildlife Fund/Brazil.
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South America and their distribution. Livingston, Nar-
berth, PA U.S.A.
Ritchison, G. and P.M. Cavanagh. 1992. Prey use by
Eastern Screech-Owls: seasonal variation in central
Kentucky and a review of previous studies. J. Raptor
Res. 26:66-73.
Ross, A. 1969. Ecological aspects of the food habits of
insectivorous screech-owls. Proc. West. Found. Vertebr.
Zool 1:301-344.
Sick, H. 1993. Birds in Brazil. A natural history. Princeton
Univ. Press, Princeton, NJ U.S.A.
Smith, S.M. 1983. Otus choliba. Pages 592-593 in D.HJanzen [Ed.], Costa Rican natural history, Univ. of
Chicago Press, Chicago, IL U.S.A.
Thomas, B.T 1977. Tropical Screech-Owl nest defense
and nestling growth rate. Wilson Bull 89:609-612.
Tolentino, M. 1967. Estudo critico sobre o clima da re-
giao de Sao Carlos. Concurso de Monograhas Muni-
cipals, Sao Carlos, Brazil.
Received 17 September 2001; accepted 5 July 2002
Associate Editor: Clint W. Boal
Letters
J. Raptor Res. 36(4):335-336
© 2002 The Raptor Research Foundation, Inc.
Comments on the First Nesting Record of the Nest of a Slaty-backed Forest-Falcon{Micrastur mirandollei) in the Ecuadorian Amazon
De Vries and Melo (2000,/. Raptor Res. 34:148-150) recently reported the first documented nest of a Slaty-backed
Forest-Falcon {Micrastur mirandollei), based on their studies in Yasuni National Park, Ecuadorian Amazon. Certain
details they reported differ markedly from the nesting habits and behavior that my colleagues and I observed for the
Barred Forest-Falcon (M. ruficollis) (Thorstrom et al. 2000a, Auk 117:781-786) and Collared Forest-Falcon (M. semi-
torquatus) (Thorstrom et al. 2000b, Ornithol. Neotrop. 11:1-12) in northern Central America, from 1988-96. These
differences are profound enough to suggest that the raptor species was possibly misidentified as a forest-falcon, or
that the Slaty-backed Forest-Falcon displays some rather uncommon behavior within the genus of Micrastur.
De Vries and Melo (2000) reported on 14 September, and again on 23 October 1997, that the nesting forest-
falcons had a changeover, implying an incubation and a brooding switch, respectively. I never recorded an incubation
or brooding switch during 8 breeding seasons of nest observations of Barred {N = 70 nesting attempts) and Collared
Forest-Falcons {N = 9 nesting attempts). For these two forest-falcons, the males’ role was providing food to the
incubating and brooding female and nestlings. During incubation, the male contact-called to the female upon his
arrival to the nest vicinity with prey, and the female exited the nest to receive the prey item where she ate it. Onrare occasions, the male entered the cavity while the female ate. The male stayed inside for several minutes either
incubating, attempting to incubate or to look at the nest contents, and then he exited the cavity prior to the female’s
return (Thorstrom 1993, M.S. thesis, Boise State University, Boise, ID U.S.A., Thorstrom et al. 2000a, Thorstrom et
al. 2000b).
De Vries and Melo (2000) suspected also that the female fed herself away from the nest and returned to take over
incubation or brooding from the male. This does not agree with my observations (Thorstrom et al. 2000a, Thorstrom
et al. 2000b) and those of Baker et al. (2000, Ornithol. Neotrop. 11:81-82). Only on very rare occasions did the female
leave the nest during incubation to feed herself when the male was late with a prey delivery and hunger brought her
off the nest (Thorstrom 1993).
De Vries and Melo (2000) describe an open nest constructed of small sticks and deep enough to hide the head
of the incubating Slaty-backed Forest-Falcon. In contrast, all described nests for the genus Micrastur have been mcavities (Mader 1979, Condor 81:320) and all nesting attempts by both Barred Forest-Falcons and Collared Forest-
Falcons observed by my colleagues and me in Central America were in tree cavities (Thorstrom et al. 1990, Condor
90:237—239, Thorstrom et al. 2000a, Thorstrom et al. 2000b) except the observation by Baker et al. (2000) of a pair
of M. ruficollis nesting in a cliff pothole below canopy level. There is also a record of a Collared Forest-Falcon nesting
in a ruined building (Cobb 1990, cited by Howell and Webb 1995, The birds of Mexico and Central America, Oxford
Univ. Press, New York, NYU.S.A.). There is one mention of stick nesting by the Lined Forest-Falcon (M. gilvicollis)
in del Hoyo et al. (1994, Handbook of the birds of the world, Lynx Edicions, Barcelona, Spain), but no details were
provided. Forest-falcons do appear to have some flexibility in their choice of nest sites, but they seem to prefer a site
that simulates a cavity; i.e., trees or cliff potholes surrounded by forests.
The Slaty-backed Forest-Falcon has several described calls: one is a 10-14 nasal aah syllables and another a two
part series '‘ah, ow, ow, ow, ow, ow, ow, uah, uah, uah, uah, uaK' (Ridgely and Gwynne 1989, A guide to the birds of
Panama, Princeton Univ, Press, Princeton, NJ U.S.A.), a chanting series 8-13 nasal, thus contrasting with the 6 calls
“kui kui kui kui kui kui' reported by de Vries and Melo (2000).
The authors’ example of the Monk Parakeet {Myiopsitta monachus), a cavity nester that builds a stick nest, does not
support their suggestion that the Slaty-backed Forest-Falcon is normally a stick nest builder. Also, their basis for
suspecting the forest-falcons built the nest is somewhat vague, i.e., “We did not see the nest being built so we did
not know if the falcons had taken an old nest made by another species, but we felt that this was unlikely because we
did not see the nest on our regular censuses” (de Vries and Melo 2000). In Central America, forest-falcons were
never observed constructing nests out of sticks or carrying nesting material (Thorstrom et al. 2000a, Thorstrom et
al. 2000b). However, it is quite possible that forest-falcons can occupy a previously-built nest in a situation that
replicates a cavity. There are six known species of Micrastur, and the Lined Forest-Falcon may represent two separate
species (A. Whittaker pers. comm.), which would make seven. Among these, two (M. ruficollis, M. semitorquatus) are
335
336 Letters VoL. 36, No. 4
known cavity nesters, three (M. plumbeus, M. gilvicollis, and the proposed new species) are suspected cavity nesters,
and for one nesting details are unknown (M. huxkl£yi). Thus, the report by de Vries and Melo (2000), stating that Mmirandollei is a stick builder and nester, contrasts sharply with the large body of evidence from its congeners.
De Vries and Melo (2000) seemed uncertain about their identification of the species they were observing on the
nest. They came to the conclusion that the birds they had observed were not Gray-bellied Goshawks {Accipiter polio-
gastei) because of the white belly and yellow facial area of the supposed female, and the other bird, the supposed
male, had buff below with both birds having long legs and three narrow, dirty white tail bands (de Vries and Melo
2000). I suggest that the characteristics that de Vries and Melo used to identify this nesting pair of raptors were not
conclusive and that they have misidentified this species. The Grey-bellied Goshawk has dark back and crown, long
yellow legs, white to gray belly and female larger than male (del Hoyo et al. 1994). Accipiters have long legs, faint
tail bands, and females are larger than males. The size dimorphism was commented on by the authors “the first
falcon was smaller and probably the male of the pair.” Sexual size dimorphism of forest-falcons was very difficult to
distinguish in the field (pers. observ.) because they are only slightly to moderately dimorphic (Thorstrom 1993). Size
dimorphism is also a characteristic described for the Grey-bellied Goshawk and Bicolored Hawk {Accipiter bicolor) (del
Hoyo et al, 1994). The authors did not give any further detailed characteristics of the color of the legs, back, eyes,
and crown of the nesting raptors. The nesting behavior and habitat, vocalization, and plumage characteristics suggest
lhat the nesting birds described by de Vries and Melo (2000) were possibly accipiters, either the Crrey-bellied Goshawkor Bicolored Hawk.
I thank The Peregrine Fund for support and L. Kiff, R. Bierregaard, J. Bednarz, and one anonymous reviewer for
their comments on this manuscript.—Russell Thorstrom, The Peregrine Fund, 5668 West Flying Hawk Lane, Boise,
ID 83709 U.S.A.; E-mail address: [email protected]
Received 21 August 2001; accepted 19 June 2002
/. RaplorRes. 36(4);337
© 2002 The Raptor Research Foundation, Inc.
Micrastur or Accipiter, That is the Question
. . the more you look the more you see” (Peter Grant 1986, Ecology and evolution of Darwin’s finches. Princeton
Univ. Press, Princeton, NJ U.S.A.).
The main point made by Thorstrorn (2002, J. Raptor Res. 36:335-336) concerns the behavior of our birds, which
he claims is not the behavior of Micrastur (he should perhaps say the behavior of M. ruficollis and M. semilorquatus,
as the behavior of the other four species is still unknown) . We can report that the Slaty-backed Forest-Falcon {Micrastur
mirandolld) was present in the area of its now defunct 1997 stick nest (de Vries and Melo 2000,/ Raptor Res. 34:148-
150) in March of 1998. Although we cannot be sure that it is the same bird we saw previously at and around the
nest, it responded (vocalized, but did not come out into the open) to the species’ call as recorded by John Mooiem his series of bird sounds of eastern Ecuador. So far, we have been unable to locate its new nesting site.
The Grey-bellied Goshawk {Accipiter poliogaster) was present at some 5 km distance from the MicrasturncA site in
both 1997 and 1998. We observed this species in the more open and bare branches of the canopy, rather than the
densely-vegetated, middle canopy layer, where we noted Micrastur mirandollei.
We hope that the comment by R. Thorstrorn (2002) stimulates more observations on Micrastur, which are badly
needed. In addition, further study on why some avian raptors are so similar in plumage patterns, as is the case with
M. mirandollei and Accipiter poliogastca; would be valuable in understanding the potential adaptive benefits of such
“mimicry.” In our field experience, the “capped” appearance and tail banding oi Accipiter 'Are diagnostic, as are the
round grey head and yellow face that Micrastur features.
—
Tjitte de Vries and Cristian Melo, Departamento de Biol-
ogia, Pontificia Universidad Catolica del Ecuador, Apartado 17-01-2184, Quito, Ecuador; E-mail address: tdevries@
puceuio.puce.edu.ee
Received 8 November 2001; accepted 27 June 2002
337
BOOK REVIEWS
J Raptor Rf,s. 36(4) :338
© 2002 The Raptor Research Foundation, Inc.
Birds of Prey; Health 8c Disease. By John E.
Cooper. 2002. 3rd edition. Blackwell, Oxford,
U.K. xvii + 345 pp., 13 tables, 56 figures, 28 color
plates, 11 appendices. ISBN 0-632-05115-9. Hard-
back, £59.50.—The study of raptors is unquestion-
ably enhanced by the diversity of perspectives from
which it derives, i.e., from biologists, falconers,
medical practitioners, and others. Each of these
disciplines provides data and references that ad-
dress birds of prey in unique and relevant terms.
In updating his earlier pioneering work, Vetmnary
Aspects of Captive Birds of Prey, now entitled Birds of
Prey: Health & Disease, John Cooper continues his
intentionally eclectic collection of information and
points-of-view. The new work is organized identi-
cally to the former but for the addition of three
new chapters from contributing authors. Roughly
one-third of the information in the new book is
repeated verbatim from the earlier one, one-third
includes previous information updated by a brief
summary of advancements and a list of references
for further study, and the remainder is an expan-
sion that reflects work that has appeared since the
earlier volume.
Cooper has long advocated collaboration amongall who deal with birds of prey, which is borne out
by his approach to the new addition. Cooper is at
once observer, historian, and medical practitioner
in discussing the various topics. He makes no at-
tempt to cover the subjects in depth, but rather
provides context and references for the reader’s
use. The diverse array of topics, and the somewhat
lack of in-depth coverage, may serve as a disap-
pointment to some but will be acceptable to others
as an interesting and general guide. The value of
the book will certainly be defined by the expecta-
tions of those who use it.
The contributed chapters vary considerably in
scope and detail. Paolo Zucca’s chapter on anato-
my is generalized with varying degrees of detail.
Once again, subjectivity is a factor in some conclu-
sions. Ian Newton’s discussion of parasitic diseases
IS, by nature, broad, yet is thorough and sound in
content. The late David Peakall’s contribution re-
garding poisonings in free-living raptors is an in-
clusive general overview of chemical toxicity on a
worldwide scale.
This is an intensely personal work. Cooper states
emphatically that he has laced the writing with
opinions, personal experiences, and other subjec-
tive matter. One of the most difficult challenges in
reviewing this work is to assign it to a category for
the reader. The book is not a clinical manual, nor
a biology text, nor a handbook for falconers. It
does, however, contain elements of each along with
personal reflections on the experiences and opin-
ions of the principal author. Although resisting
classification. Birds of Prey: Health & Disease fills a
useful and interesting niche in raptor literature for
all those involved in the field.
—
James D. Elliott,
South Carolina Center for Birds of Prey, P.O. Box1247, Charleston, SC 29402 U.S.A.
J. Raptor Res. 36(4):338-339
© 2002 The Raptor Research Foundation, Inc.
Owls. By Floyd Scholz. 2001. Stackpole Books,
Mechanicsburg, PA. xiii + 379 pp., more than 700
color photographs. ISBN 0-8117-102T1. Cloth,
$80.00.—In 1993, Floyd Scholz published Birds of
Prey, which was a collection of detailed color pho-
tographs of 17 species of North American falconi-
forms (see /. Raptor Res. 28:278—279, 1994). Team-
ing up once more with photographer Tad Merrick,
Scholz has expanded his domain to include the
strigiforms. The result is an extensive series of col-
or photographs of 17 of the 19 species of owls
(Western Screech-Owl \_Otus kennicottii] and Whis-
kered Screech-Owl [O. trichopsis] omitted) that
breed in the United States and Canada.
Floyd Scholz is an extraordinary carver and
painter of birds, and the main purpose of Owls is
to serve as a reference guide for artists. An intro-
338
December 2002 Book Reviews 339
ductory chapter, “What is an Owl?” presents infor-
mation on the various morphological adaptations
of owls; the treatment enhances the text and is ba-
sically the same as that found in any coffee table
book or general ornithology text that deals with
owls. The species accounts make up the heart of
the book. Each includes a page of information on
morphology and behavior of the species in ques-
tion, details on the size of various body parts (in-
cluding line drawings of the species from the back
and side), and numerous color photographs (typ-
ically 30-40 per species). The photos are taken
from nearly every conceivable angle to provide de-
tails on plumage, talons, ear tufts, facial ruffs, eyes,
bills, nostrils, and napes, to name but a sample of
the features depicted. These photos contain fine
points that would seldom be noticed without hav-
ing a bird in the hand and thus will serve as a
valuable reference for people who do not have ac-
cess to museum specimens. Most of the photos are
of captive birds, the exceptions being a handful of
very nice shots of wild Northern Hawk Owls (Sur-
nia ulula)
,
Great Gray Owls {Strix nebulosa), and
Boreal Owls {Aegolius funereus) by Ron Austing and
Robert Taylor.
The photo selection, and the photos themselves,
are truly excellent, but two criticisms are worth
mentioning. First, the Great Horned Owl {Bubo vir-
ginianus) shown in many of the photos can be
readily described by two words: pissed off. Tm not
sure why an artist would need photos of an owl in
this state, nor why someone would continue to
bother a bird that so obviously detested whatever
treatment it was receiving. In fairness to the author
and photographer, this same attitude is displayed
by a wild female Great Horned Owl depicted onthe cover of the Birds of North America species ac-
count. Second, I was surprised that none of the 32
photos of the two species of pygmy-owls contained
a decent view of the so-called “false eyes” on the
back of the head. This is a minor quibble to be
sure, but an opportunity missed nonetheless.
The last two chapters are entitled “Techniques
for the Artist and Garver” and “Gallery,” the latter
consisting of a collection of photos of some of the
owls Mr. Scholz has carved and painted. The carv-
ings are absolutely gorgeous and point to the enor-
mous talent of the author. This book will appeal to
anyone with an interest in owls, although the price
may place it out of reach of all but the confirmed
“owlaholics,” to borrow a phrase coined by HeimoMikkola.
—
Jeff Marks, Montana Cooperative Wild-
life Research Unit, University of Montana, Missou-
la, MT 59812 U.S.A.
J Raptor Res. 36(4);340—343
© 2002 The Raptor Research Foundation, Inc.
Journal of Raptor Research
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Table titles must be complete sentences.
Use same size of type as in text.
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VII. Figure Legends
Print all figure legends on one page, double
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Number using Arabic numbers consecutively in
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VIII. Preparation of Illustrations
(Illustrations are referred to as figures and include
drawings, graphs, and black and white half-tones
[photographs] . CONSULT THE EDITOR IN AD-VANCE ABOUT COLOR.)
Use professional standards in preparing figures,
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lustrations (Allen Press, PO. Box 368, Lawrence,
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Plan figures to fit proportions in the JRR, pref-
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December 2002 Information for Contributors 343
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J RaplorRes. 36(4):M4-350
© 2002 The Raptor Research Foundation, Inc.
Index to Volume 36
By Kristina Baker
This index includes references to general, species, common names, key words, and authors. Reference is also madeto book reviews, letters, and reviewers. Taxa other than raptors are included where referenced by authors.
A
Abuladze, Alexander and Jevgeni Shergalin, The Golden
Eagle in north Caucasia and Transcaucasia, 10-17
(suppl.)
Afdpiler, 229-230
(ooperii 229-230
gentilis, 141-143, 229-230, 265-279
sLriaius, 229-230
Aegolius funereus, 2 1 8—2 1
9
Age differences, 115-120
Agostini, Nicolantonio, Luca Baghino, Charles Coleiro,
Ferdinando Corbi, and Guido Premuda, Circuitoxis
autumn migration in the Short-toed Eagle { Circaetus
gallicus), 111-114
Alaska, 50-54 (suppl.)
Albinism, 200-202
Alloparental care, 70-73
Ammer, Frank K. and Petra Bohall Wood, Probable
breeding of Short-eared Owls in southern West Vir-
ginia, 237-238
Andersen, David E., see Warnke, D. Keith
Anderson, David L., see Thorstrom, Russell
Angulo, Elena, Factors influencing length of the pc^st-
fledging period and timing of dispersal in Bonelli’s
Eagle {Hieraaetus fasciatus) in southwestern Spain,
157
Anthropogenic food sources, 220-224
Aparicio, Jose, see Cordero, Pedro J.
Apodaca, Christine K., see Seavy, Nathaniel E.
Aquila dirysaetos, 3-9 (suppl.), 10-17 (suppl.), 18-19
(suppl.), 20-24 (suppl.), 25-28 (suppl.), 29-31
(suppl.), 32-40 (suppl.), 41-49 (suppl.), 50-54
(suppl.), 55-61 (suppl.), 62-69 (suppl.), 70-77
(suppl.)
xvahlbergi, 51—57
Argentina, 206-212, 315-319
Asia otus, 73-77
Athene cunicularia Jloridana, 3-10
Avila, Gregorio Lopez, see Whitacre, David F.
Avila, Juventino Lopez, see Whitacre, David F.
Avery, Michael L., John S. ITiimphrey, Eric A. Tillman,
Kimberly O. Phares, and Jane E. Hatcher, Dispersing
vulture roosts on communication towers, 45-50
Ayers, Serena, see Thorstrom, Russell
B
Baghino, Luca, see Agostini, Nicolantonio
Bainbridge, Ian R, see McGrady, Michael J.
Baja California Peninsula, 3-9 (suppl.)
Baker, Aaron, see Thorstrom, Russell
Balbontin, Javier and Miguel Ferrer, Plasma chemistry
reference values in free-living Bonelli’s Eagle {Hi-
eraaetus fasciatus) nestlings, 231-235
Bald and Golden Eagle Protection Act, 29-31 (suppl.)
Band, encounters, 97-110
recoveries, 97-110
Barry, Irene M., see Powell, Larkin A.
Barton, Nigel W.H., Nicholas C. Fox, Peter F. Surai, and
Brian K. Speake, Vitamins E and A, carotenoids, and
fatty acids of the raptor egg yolk, 33-38
Bates, John M., see Grifliths, Carole S.
Bats, 146-148
Beasom, Sam. L, see Proudfoot, Glenn A.
Bechard, MareJ. and Michael J. McGrady, Status and con-
servation of Golden Eagles, 2 (suppl.)
Bednarz, James C., Working toward excellence, 1-2
Behavior, 77-81, 121-127, 136-139
copulation, 66-70
hunting, 194-199
ranging, 70-77 (suppl.)
Beheim, Janne, Katrine Eldegard, Gro Bj0rnstad, Mats
Isaksson, Geir Sonerud, Olav Heie, and Helge
Klungland, DNA polymorphisms in Boreal Owls {Ae-
golius funereus) ,2 1 8—2 1
9
Bellocq, M. Isabel, Patricio Ranhrez-Llorens, andjulieta
Filloy, Recent records of Crowned Eagles {Harpyhal-
iaetus coronalus) from Argentina, 1981-2000, 206-
212
Berkelman, James, James D. Fraser, and Richard T. Wat-
son, Nesting and yjerching habitat use of the Mada-
gascar Fish-Eagle, 287-293
Bertram, Joan and Antoni Margalida, Social organization
of a trio ol Bearded Vultures {Gypaetus barbatus): sex-
ual and parental roles, 66-70
Bianchi, Edward W., see Hunt, W. Grainger
Bias, 11-16
Bildstein, Keith 1.., sec Yosef, Reuven
Bj0rnstad, Gro, see see Beheim, Janne
Blood, 231-235
parasites, 139-141
Bloxton, Thomas D., Audi Rogers, Michael F. Ingraldi,
344
December 2002 Index to Volume 36 345
Steve Rosenstock, John M. Marzluff, and Sean RFinn, Possible choking mortalities of adult Northern
Goshawks, 141-143
Boano, Giovanni and Roberto Toffoli, A line transect sur-
vey of wintering raptors in the western Po Plain of
northern Italy, 128-135
Bogliani, Giuseppe, see Sergio, Fabrizio
Bolivia, 146-148
Boto, Alberto, see Sergio, Fabrizio
Brazil, 328-331, 332-334
Breeding, 161-169
diet, 332-334
season, 194-199
success, 24-32, 81-84, 224-228
Brendel, Ulrich M., Rolf Eberhardt, and Karen Wies-
mann, Conservation of the Golden Eagle (Aquila
chrysaetos) in the European Alps—a combination of
education, cooperation, and modern techniques,
20-24 (suppl.)
Bubo bubo, 11-16
virginianus, 58—65
Buhay, Jennifer E. and Gary Ritchison, Hunting behavior
of and space use by Eastern-Screech Owls during the
breeding season, 194—199
Buteo buteo, 24-32, 115-120, 128-135, 188-193
lineatus, 152-153
C
Calvert, Dan J., see Powell, Larkin A,
Canada, 32-40 (suppl.)
Canary Islands, 17-23
Cannibalism, 200-202
Capote, Nieves, see Donazar, Jose Antonio
Capture, 188-193
techniques, 320-323
Caracara cheriway, 203—206
Carpathian Mountains, 25—28 (suppl.)
Carrion, 152-153
Caryospora hutzeri, 84—86
Cathartes aura, 45-50, 144—145
burrovianus, 183-187
melambrotus, 183-187
Caucasia, 10-17 (suppl.)
Ceballos, Olga, see Donazar, Jose Antonio
Central America, 39-44
Chavez-Ramirez, Felipe, see Proudfoot, Glenn A.
Chihuahua, 3-9 (suppl.)
Chile, 315-319
Choking, 141-143
Circaetus gallicus, 111-114
Cliffs, 39-44
Coahuila, 3-9 (suppl.)
Coccidiosis, 84—86
Coleiro, Charles, see Agostini, Nicolantonio
Colonization, 18-19 (suppl.)
Colorado, 256-264
Columbretes Islands, 139-141
Common Buzzard, 24—32, 115-120, 128-135, 188-193
Communication tower, 45-50
Conservation, 10-17 (suppl.), 20-24 (suppl.), 29-31
(suppl.), 41-49 (suppl.), 51-57, 206-212
Constraints, 41-49 (suppl.)
Control region, 17-23
Cooke, Raylene, Robert Wallis, and John White, Use of
vegetative structure by Powerful Owls in outer urban
Melbourne, Victoria, Australia—implications for
management, 294-299
Coragyps atratus, 45-50
Corbi, Charles, see Agostini, Nicolantonio
Cordero, Pedro J., Jose M. Aparicio, and David T. Parkin,
Genetic evidence of alloparental care of a female
Lesser Kestrel in an alien nest, 70-73
Coulson, Jennifer O., Mississippi Kites use Swallow-tailed
Kite nests, 155—156
Crested Caracara, 203-206
Cromrich, Lee A., Denver W. Holt, and Shawne M. Lea-
sure, Trophic niche of North American Great
Horned Owls, 58-65
Culver, Melanie, see Tingay, Ruth E.
Cumulative impacts, 55-61 (suppl.)
Cytochrome b, 183-187
D
Dams, 245-255
de Vries, Tjitte and Cristian Melo, Micrastur or Accipiter,
that is the question, 337
Deforestation, 51-57
Degraaf, Richard M., see Smith, Harvey R.
Demography, 3-10
Denali National Park, 50-54 (suppl.)
Density, 24—32
Development, 3-10, 77-81
Dho-gaza, 320-323
Diet, 24-32, 58-65, 148-152, 328-331
assessment methods, 11-16
Dispersal, 176-182, 309-314
natal, 203—206
roost, 45-50
Distribution, 10-17 (suppl.)
Disturbance, 294—299
DNA, fingerprinting, 280-286
mitochondrial, 17—23
multilocus fingerprinting, 70-73
polymorphisms, 218-219
Donazar, Jose Antonio, Juan Jose Negro, Cesar Javier Pa-
lacios, Laura Gangoso,Jose Antonio Godoy, Olga Ce-
ballos, Fernando Hiraldo, and Nieves Capote, De-
scription of a new subspecies of the Egyptian Vulture
(Accipitridae: Neophron percnopterus) from the Canary
Islands, 17-23
Driscoll, Daniel E., see Hunt, W. Grainger
Durango, 3-9 (suppl.)
346 Index to Volume 36 VoL. 36, No. 4
Dykstra, Cheryl R., Michael W. Meyer, and D. Keith Warn-
ke, Bald Eagle reproductive performance following
video camera placement, 136-139
Dykstra, Cheryl R., see Warnke, D. Keith
E
Eagle, Bald, 29-31 (suppL), 121-127, 136-139, 161-169,
245-255, 256-264, 324-327
Bonelli’s, 231-235
Crested, 77-81
Crowned, 206-212
Crowned Hawk-, 300—308
Golden, 3-9 (suppL), 10-17 (suppL), 18-19 (suppl.),
20-24 (suppl.), 25-28 (suppl.), 29-31 (suppl.),
32-40 (suppl.), 41-49 (suppl.), 50-54 (suppl.),
55-61 (suppl.), 62-69 (suppl.), 70-77 (suppl.)
Long-crested, 51-57
Madagascar Fish-, 280-286, 287-293, 309-314
Short-toed, 111-114
Wahlberg’s, 51-57
White-tailed Sea, 220-224
Eberhart, Rolf, see Brendel, Ulrich M.
Effigy, 45-50
Eggs, 324-327
yolk, 33-38
Eggshell characteristics, 324-327
Elat, 115-120
Eldegard, Katrine, see Beheim, Janne
Elliot, James D., A review of Birds of Prey: Health & Dis-
ease, by John E. Cooper, 2002, 338
Elhs, David H., Beth Ann Sabo, James K. Fackler, and
Brian A. Millsap, Prey of the Peregrine Falcon {Falco
peregtinus cassini) in southern Argentina and Chile,
315-319
Ellis, David H., Lynn W. Oliphant, and James K. Fackler,
Schizochromism in a Peregrine Falcon from Arizo-
na, 200-202
Emergent trees, 300-308
Englund, Judy Voigt, see Martell, Mark S.
Environmental education, 20-24 (suppl.)
European Alps, 20-24 (suppl.)
F
Fackler, James K., see Ellis, David H., 200-202
Fackler, James K., see Ellis, David H., 315-319
Fahler, Natalie A. and Lester D. Flake, Nesting of Long-
eared Owls along the lower Big Lost River, Idaho: a
comparison of 1975-76 and 1996-97, 73-77
Falco deiroleucus, 39-44
eleonorae, 139-141
naumanni, 70-73, 148-152
peregtinus, 176-182, 200-202, 203-217, 315-319
tinnunculus, 81—84, 84-86
Falcon, Eleonora’s, 139-141
Orange-breasted, 39-44
Pallid, 315-319
Peregrine, 176-182, 200-202, 213-217, 315-319
Fatty acids, 33-38
Feeding, 144-145, 152-153
habits, 224-228
Ferrer, Miguel, see Balbontin, Javier
Filloy, Julieta, see Bellocq, M. Isabel
Finn, Sean R, Daniel E. Varland, and John M. Marzluff,
Does Northern Goshawk breeding occupancy vary
with nest-stand characteristics on the Olympic Pen-
insula, Washington?, 265-279
Finn, Sean R, see Bloxton, Thomas D.
Firmanszky, Gabor, The status of the Golden Eagle {Aq-
uila chrysaetos) in Hungary, 18-19 (suppl.)
Flake, Lester D., see Fahler, Natalie A.
Flocking, 111-114
Florida, 3-10, 203-206
Flyways, 97-110
Food, 144-145
-niche breadth, 58-65
Foraging habitat, 220-224
Forestry, 24—32
Fox, Nicholas C., see Barton, Nigel W.H.
Fractures, 229-230
Framework, 41—49 (suppl.)
Fraser, James D., see Berkelman, JamesFraser, James D., see Tingay, Ruth E.
French, Thomas W., see Roth, Aaron J.
G
Gangoso, Laura and Cesar J. Palacios, Endangered Egyp-
tian Vulture {Neophron percnopterus) entangled in a
power line ground-wire stabilizer, 238-239
Gangoso, Laura, see Donazar, Jose Antonio
Genetics, 183-187
Gladdium brasilianum, 170-175
Godoy, Jose Antonio, see Donazar, Jose Antonio
Grant, Justin R., see McGrady, Michael J.
Great Lakes, 136-139
Griffiths, Carole S. and John M. Bates, Morphology, ge-
netics and the value of voucher specimens: an ex-
ample with Cathartes vultures, 183-187
Gypaetus barbatus, 66-70
H
Habitat, 287-293
management, 55-61 (suppl.)
preferences, 224-228
quality models, 20-24 (suppl.)
selection, 245-255
use, 51-57
Haliaeetus albicilla, 220-224
leucocephalus, 29-31 (suppl.), 121-127, 136-139, 161-
169, 245-255, 256-264, 324-327
vociferoides, 280-286, 287-293, 309-314
Hallerman, Eric M., see Tingay, Ruth E.
December 2002 Index to Volume 36 347
Harmata, Alan R., Vernal migration of Bald Eagles from
a southern Colorado wintering area, 256-264
Harpyhaliaetus coronatus, 206-212
Hatcher, Jane E., see Avery, Michael L.
Hawk, Cooper’s, 229-230
Red-shouldered, 152-153
Sharp-shinned, 229-230
Heie, Olav, see see Beheim, Janne
Hieraaetus fasciatus, 231-235
Hiraldo, Fernando, see Donazar, Jose Antonio
Hoffman, Stephen W., Jeff R Smith, and Timothy D.
Meehan, Breeding grounds, winter ranges, and mi-
gratory routes of raptors in the mountain west, 97-
110
Hokkaido, Japan, 220-224
Holt, Denver W., see Cromrich, Lee A.
Home range, 70-77 (suppL), 245-255
Homosexual matings, 66-70
Humphrey, John S., see Avery, Michael L.
Hungary, 18-19 (suppl.)
Hunt, W. Grainger, Ronald E. Jackman, Daniel E. Dris-
coll, and Edward W. Bianchi, Foraging ecology of
nesting Bald Eagles in Arizona, 245-255
I
Idaho, 73-77
Immobilization, 188-193
Ingraldi, Michael R, see Bloxton, Thomas D.
Injuries, 229-230
Isaksson, Mats, see Beheim, Janne
Italy, 11-16, 24-32, 128-135
J
Jackman, Ronald E., see Hunt, W. Grainger
Jacobs, Eugene A. and Glenn A. Proudfoot, An elevated
net assembly to capture nesting raptors, 320-323
Janovsky, Martin, Thomas Ruf, and Wolfgang Zenker,
Oral administration of tiletamine/zolazepam for the
immobilization of the Common Buzzard {Buteo bu-
teo), 188-193
Jenkins, M. Alan, Steve K. Sherrod, David A. Wiedenfeld,
and Donald H. Wolfe, Jr., Florida Bald Eagle {Hal-
iaeetus leucocephalus) egg characteristics, 324-327
Jones, Gwilym S., see Roth, Aaron J.
K
Karasov, William H., see Warnke, D. Keith
Kery, Marc, New observations of the Peregrine Falcon
{Falco peregrinus) in Peru, 213-217
Kestrel, Eurasian, 81-84, 84-86
Lesser, 70-73, 148-152
Klungland, Helge, see see Beheim, Janne
Kochert, Michael N. and Karen Steenhof, Golden Eagles
in the G.S. and Canada: status, trends, and conser-
vation challenges, 32-40 (suppl.)
Kopij, Grzegorz, Food of the l,esser Kestrel {Falco nau-
manni) in its winter quarters in South Africa, 148-
152
Krone, Oliver, Fatal Caryospora infection in a free-living
Juvenile Eurasian Kestrel {Falco tinnunculus)
,
84—86
L
land use, 55-61 (suppl.)
Landaeta, Carlos A., see Vargas, Julieta
Leasure, Shawne M., see Cromrich, Lee A.
Leucism, 200-202
Linda, Lomo, see Nunnery, Tony
Logistic regression, 265-279
Londei, Tiziano, The Fox Kestrel {Falco alopex) hovers,
236-237
Lophaetus occipitalis, 51-57
M
Madagascar, 287-293
Madders, Mike and Dave Walker, Golden Eagles in a mul-
tiple land-use environment: a case study in conflict
management, 55-61 (suppl.)
Malan, Gerard and Susanne Shultz, Nest-site selection of
the Crowned Hawk-Eagle in the forests of Kwazulu-
Natal, South Africa, and Tai, Ivory Coast, 300-308
Management, 20-24 (suppl.), 294—299
Manganaro, Alberto, see Salvati, Luca
Mangrove, 328-331
Marches!, Luigi, Paolo Pedrini, and Fabrizio Sergio, Bi-
ases associated with diet study methods in the Eur-
asian Eagle Owl, 11-16
Margalida, Antoni, see Bertran, Joan
Mark-recapture, 3-10
model, 176-182
Marks, Jeff, A review of Owls, by Floyd Scholz, 2001, 338-
339
Martell, Mark S., Judy Voigt Englund, and Harrison B.
Tordoff, An urban Osprey population established by
translocation, 91—96
Martinez-Abrain, Alejandro and Gerardo Urios, Absence
of blood parasites in nestlings of the Eleonora’s Fal-
con {Falco eleonorae), 139-141
Marzluff, John M., a review of The Spanish Imperial Ea-
gle, by Miguel Ferrer, 2001, 242-244
Marzluff, John M., see Bloxton, Thomas D.
Marzluff, John M., see Finn, Sean P.
Mating system, 280-286
Mays, Jody L., see Proudfoot, Glenn A.
McAllister, Kelly R., see Watson, James W.
McGrady, Michael J., Justin R. Grant, Ian P. Bainbridge,
and David R.A. McLeod, A model of Golden Eagle
{Aquila chrysaetos) ranging behavior, 62-69 (suppl )
McGrady, Michael J., see Bechard, MarcJ.
McGrady, Michael J., see McLeod, David R.A
McIntyre, Carol L., Patterns in nesting area occupancy
and reproductive success of Golden Eagles {Aquila
348 Index to Volume 36 VOL. 36, No. 4
chrysaetos) in Denali National Park and Preserve,
Alaska, 1988-99, 50-54 (suppl.)
McLeod, David R.A., D. Philip Whitfield, and Michael J.
McGrady, Improving prediction of Golden Eagle
{Aquila chrysaetos) ranging in western Scotland using
GIS and terrain modeling, 70-77 (suppl.)
McI.eod, David R.A., see McGrady, Michael J.
Mediterranean areas, 81-84
Meehan, Timothy D., see Hoffman, Stephen W.
Melo, Cristian, see de Vries, Tjitte
Mexico, 3-9 (suppl.)
Meyer, Michael W., see Dykstra, Cheryl R.
Meyer, Michael W., see Warnke, D. Keith
Microsatellite, 218-219
Migration, 97-110, 111-114
differential, 97-110
spring, 115-120
vernal, 256-264
Millar, Jody Gustitus, The protection of eagles and the
Bald and Golden Eagle Protection Act, 29-31
(suppl.)
Miller, Richard S., see Smith, Harvey R.
Millsap, Brian A., see Ellis, David H.
Millsap, Brian A., Survival of Florida Burrowing Owls
along an urban-development gradient, 3-10
Minnesota, 91-96
Mizera, Tadeusz, see Waclawek, Krzysztof
Monitoring, 32-40 (suppl.)
Morphnus guianensis, 77-81
Morrison, Joan L., see Nemeth, Nicole M.
Mortality, 32-40 (suppl.), 141-143
Mottajunior, Jose Carlos, Diet of breeding Tropical
Screech-Owls (Otus choliba) in southeastern Brazil,
332-334
Movements, 62-69 (suppl.)
N
Navigation, 111-114
Negro, Juan Jose, see Donazar, Jose Antonio
Nemeth, Nicole M. andjoan L. Morrison, Natal dispersal
of the Crested Caracara {Caracara cheriway) in Flori-
da, 203-206
Neofjhron percnopterus majormsis, 1 7-23
Nest, access, 300-308
helper, 280-286
tree, 287-293
Nest-site selection, 300-308
Nesting, 73-77
biology, 77-81
Nestlings, 77-81, 139-141
free-living, 231-235
Net, drop, 320-323
elevated, 320-323
mist, 320-323
New records, 206-212
Ntnox strenua, 294—299
North America, 58-65, 229-230
western, 97-110
Northern Goshawk, 141-143, 229-230, 265-279
Nunnery, Tony, Lomo Linda, and Mark R. Welford,
Barred Forest-Falcon {Micrastur ruficollis) predation
on a hummingbird, 239-240
O
Olfaction, 144-145
Oliphant, Lynn W., see Ellis, David H.
Olmos, Fabio, see Silva e Silva, Robson
Oral administration, 188-193
Orientation, 111-114
Osprey, 91-96, 328-331
Otus asio, 194-199
choliba, 332-334
Overstory depth, 265-279
Owens, Thomas E., see Watson, James W.
Owl, Barn, 146-148, 224-228
Boreal, 218-219
Burrowing, 3-10
Eastern Screech-, 194-199
Eurasian Eagle-, 11-16
Ferriginous Pygmy-, 170-175
Great Horned, 58-65
Long-eared, 73-77
Mechanical, 320—323
Powerful, 294-299
Tengmalm’s, 218-219
Tropical Screech-, 332-334
P
Palacios, Cesar Javier, see Donazar, Jose Antonio
Palacios, Cesar J., see Gangoso, Laura
Pandion haliaetus, 91-96, 328-331
Parental roles, 66-70
Parkin, David T, see Cordero, Pedro J.
Pedrini, Paolo, see Marches!, Luigi
Perch time, 194—199
tree, 287-293
Peru, 213-217
Pesticides, 324-327
Phares, Kimberly O., see Avery, Michael L.
Piscivory, 245-255
Plasma, 33-38
chemistry, 231-235
Poland, 25-28 (suppl.)
Polyandry, 280-286
cooperative, 66-70
Population restoration, 176-182
Post-fledging, length, 157
movement, 220-224
status, 161-169
Powell, Larkin A., Dan J. Calvert, Irene M. Barry, and
Lowell Washburn, Post-fledging survival and dispers-
Dec;ember 2002 Index to Voeume 36 349
al of Peregrine Falcons during a restoration project,
176-182
Pranty, Bill, Red-shouldered Hawk feeds on carrion, 152-
153
Pre-Alps, 24-32
Premuda, Guido, see Agostini, Nicolantonio
Prey, 141-143, 315-319
biomass, 332-334
size, 146-148
Productivity, 91-96, 161-169
Protozoa, 84-86
Proudfoot, Glenn A., Sam L, Beasom, Felipe Chavez-Ra-
mirez, and Jody L. Mays, Response distance of Fer-
ruginous Pygmy-Owls to broadcasted conspecific
calls, 170-175
Proudfoot, Glenn A., see Jacobs, Eugene A.
Provisioning, 121-127
R
Radio-tracking, 256-264
Radiotelemetry, 245-255
Rafanomezantsoa, Simon, Richard T. Watson, and Russell
Thorstrom, Juvenile dispersal of Madagascar Fish-Ea-
gles tracked by satellite telemetry, 309-314
Ramirez-Llorens, Patricio, see Bellocq, M. Isabel
Ranazzi, Lamberto, see Salvati, Luca
Range, 62-69 (suppl.)
model, 70-77 (suppl.)
use, 194-199
Raptor nutrition, 33-38
Raptors, 128-135
Recovery, 161-169
Repopulation, 25-28 (suppl.)
Reproduction, 50-54 (suppl.)
Reproductive performance, 136-139
Restani, Marco, A review of Raptors of the World, by
James Ferguson-Lees and David A. Christie, 2001,
241-242
Riparian, 73-77
Ritchison, Gary, see Buhay, Jennifer E.
Rivers, 245-255
Rodriguez-Estrella, Ricardo, A survey of Golden Eagles in
northern Mexico in 1984 and recent records in cen-
tral and southern Baja California Peninsula, 3-9
(suppl.)
Rogers, Andi, see Bloxton, Thomas D.
Rome, 224-228
Rosenstock, Steve, see Bloxton, Thomas D.
Roth, Aaron J., Gwilym S. Jones, and Thomas W. French,
Incidence of naturally-healed fractures in the pec-
toral bones of North American Accipiters, 229-230
Ruf, Thomas, see Janovsky, Martin
S
Sabo, Beth Ann, see Ellis, David H.
Salvati, Luca, Lamberto Ranazzi, and Alberto Manganaro,
Habitat preferences, breeding success, and diet of
the Barn Owl ( Tyto alba) in Rome: urban versus rural
territories, 224-228
Salvati, Luca, Spring weather and breeding success of the
Eurasian Kestrel {Falco tinnunculus) in urban Rome,Italy, 81-84
Saskatchewan, 256-264
Satellite telemetry, 309-314
Scandolara, Chiara, see Sergio, Fabrizio
Scavenging, 144-145
Schizochromism, 200-202
Scotland, 62-69 (suppl.)
Seavy, Nathaniel E. and Christine K. Apodaca, Raptor
abundance and habitat use in a highly-disturbed- for-
est landscape in western Uganda, 51-57
Sergio, Fabrizio, Alberto Boto, Chiara Scandolara, and
Guiseppe Bogliani, Density, nest sites, diet, and pro-
ductivity of Common Buzzards {Buteo buteo) in the
Italian pre-Alps, 24-32
Sergio, Fabrizio, see Marchesi, Luigi
Sex, 231-235
Shergalin, Jevgeni, see Abuladze, Alexander
Sherrod, Steve K., see Jenkins, M. Alan
Shiraki, Saiko, Post-fledging movements and foraging
habitats of immature White-tailed Sea Eagles in the
Nemuro Region, Hokkaido, Japan, 220-224
Shoreline, 297-293
Shrub cover, 265-279
Shultz, Susanne, see Malan, Gerard
Silva e Silva, Robson, and Fabio Olmos, Osprey ecology
in the mangroves of southeastern Brazil, 328-331
Simonetti, Javier A., see Vargas, Julieta
Smith, Harvey R., Richard M. DeGraaf, and Richard S.
Miller, Exhumation of food by Turkey Vulture, 144-
145
Smith, Jeff R, see Hoffman, Stephen W.
Solifugae, 148-152
Sonerud, Geir, see Beheim, JanneSonora, 3-9 (suppl.)
South Africa, 148-152
South America, 213-217
Spain, 66-70
Speake, Brian K., see Barton, Nigel W.H.
Status, 32-40 (suppl.), 206-212
Steenhof, Karen, A review of The Raptor Almanac, by
Scott Weidensaul, 2000, 87-88
Steenhof, Karen, see Kochert, Michael N.
Stephanoaetus coronatus, 300—308
Stinson, Derek, see Watson, James W.Subspecies, 17-23
Surai, Peter E, see Barton, Nigel W.H.
Survey, 39-44
broadcast, 170-175
roadside, 51-57
winter, 128-135
Survival, 3-10, 176-182
350 Index to Volume 36 VoL. 36, No. 4
T
Tea plantation, 51-57
Temperature, 294-299
Territoriality, 62-69 (suppl.)
Territories, 224-228
Thorstrom, Russell, Comments on the first nesting re-
cord of the nest of a Slaty-backed Forest-Falcon {Mi-
crastur mirandollei) in the Ecuadorian Amazon, 335-
336
Thorstrom, Russell, Richard Watson, Aaron Baker, Ser-
ena Ayers, and David L. Anderson, Preliminary
ground and aerial surveys for Orange-breasted Fal-
cons in Central America, 39-44
Thorstrom, Russell, see Rafanomezantsoa, Simon
Tiletamine, 188-193
Tillman, Eric A., see Avery, Michael L.
Time budgets, 121-127
Tmgay, Ruth E., Melanie Culver, Eric M. Hallerman,
James D. Fraser, and Richard T. Watson, Subordinate
males sire offspring in Madagascar Fish-Eagle {Hal-
iaeetus vociferoides) polyandrous breeding groups,
280-286
Toffoli, Roberto, see Boano, Giovanni
Tordoff, Harrison B., see Martell, Mark S.
Transect, 128-135
Translocation, 91-96
Tropical, 77-81
Tryjanowski, Piotr, see Yosef, Reuven
Tyto alba, 146-148, 224-228
U
Uganda, 51-57
Urban, habitats, 81-84, 224—228
wildlife, 91-96
wildlife management, 3-10
Urbanization, 294—299
Urios, Gerardo, see Martinez-Abrain, Alejandro
U.S., 32-40 (suppl.)
V
Vargas, Julieta, Carlos Landaeta A., and Javier A. Simo-
netti. Bats as prey of Barn Owls { Tyto alba) in a trop-
ical savanna in Bolivia, 146-148
Variability, 218-219
Varland, Daniel E., see Finn, Seair P.
Vegetation structure, 294-299
Video camera, 136-139
Vitamins, 33-38
Voucher specimens, 183-187
Vultures, 45-50
Bearded, 66-70
Egyptian, 17-23
Turkey, 144—145
Yellow-headed, 183-187
WWaclawek, Krzysztof and Tadeusz Mizera, The status of
the Golden Eagle {Aquila chrysaelos) in Poland, 25-
28 (suppl.)
Wallis, Robert, see Cooke, Raylene
Warnke, D. Keith, David E. Andersen, Cheryl R. Dykstra,
Michael W. Meyer, and William H. Karasov, Provi-
sioning rates and time budgets of adult and nestling
Bald Eagles at inland Wisconsin nests, 121-127
Warnke, D. Keith, see Dykstra, Cheryl R.
Washburn, Lowell, see Powell, Larkin A.
Washington, 161-169, 265-279
Watson, James W., Derek Stinson, Kelly R. McAllister, and
Thomas E. Owens, Population status of Bald Eagles
breeding in Washington at the end of the 20^’^ cen-
tury, 161-169
Watson, Jeff and Philip Whitfield, A conservation frame-
work for the Golden Eagle {Aquila chrysaetos) in Scot-
land, 41-49 (suppl.)
Watson, Richard, see Thorstrom, Russell
Watson, Richard T., see Berkelman, James
Watson, Richard T., see Rafanomezantsoa, Simon
Watson, Richard T., see Tingay, Ruth E.
Weather conditions, 81-84
Welford, Mark R., see Nunnery, Tony
Whitacre, David R, Juventino Lopez Avila, and Gregorio
Lopez Avila, Behavioral and physical development of
a nestling Crested Eagle {Morphnus guianensis)
,
77—
81
White, John, see Cooke, Raylene
Whitheld, D. Philip, see McLeod, David R.A.
Whitfield, Philip, see Watson, Jeff
Wiedenfeld, David A., see Jenkins, M. Alan
Wiesmann, Karen, see Brendel, Ulrich M.
Wildlife, habitat relationships, 265-279
management, 300-308
Wind energy, 55-61 (suppl.)
Winter quarters, 148-152
Wintering, 256-264
ecology, 328-331
Wisconsin, 121-127
Wolfe, Jr., Donald H., see Jenkins, M. Alan
Wood, Petra Bohall, see Ammer, Frank K.
Y
Yosef, Reuven, Piotr Tryjanowski, and Keith Bildstein,
Spring migration of adult and immature buzzards
{Buteo buteo) through Elat, Israel; timing and body
size, 115-120
Z
Zacatecas, 3-9 (suppl.)
Zemplen Mountains, 18-19 (suppl.)
Zenker, Wolfgang, see Janovsky, Martin
Zolazepam, 188-193
Zones, 41-49 (suppl.)
THE JOURNAL OF RAPTOR RESEARCHA QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.
(Founded 1966)
EDITOR IN CHIEFJames C. Bednarz
James R. Belthoff
Clint W. Boal
Joan L. Morrison
Juan Jose Negro
ASSOCIATE EDITORSMarco Restani
Ian G. WarrentinTroy I. Wellicome
BOOK REVIEW EDITORJeffrey S. Marks
CONTENTS FOR VOLUME 36, 2002
Number 1
Editor’s Page: Working Toward Excellence. James C. Bednarz 1
Survival of Florida Burrowing Owls Along an Urban-Development Gradient.
Brian A. Millsap 3
Biases Associated with Diet Study Methods in the Eurasian Eagle-Owl. Luigi
Marchesi, Paolo Pedrini, and Fabrizio Sergio 11
Description of a New Subspecies of the Egyptian Vulture (Accipitridae; Neo-
phron fercnopterus) FROM THE Canary Islands. Jose Antonio Donazarjuan Jose Negro,
Cesar Javier Palacios, Laura Gangoso, Jose Antonio Godoy, Olga Ceballos, Fernando Hiraldo, and
Nieves Capote 17
Density, Nest Sites, Diet, and Productivity of Common Buzzards {Bijteo buteo)
in the Italian Pre-Alps. Fabrizio Sergio, Alberto Boto, Chiara Scandolara, and Giuseppe
Bogliani 24
Vitamins E and A, Carotenoids, and Fatty Acids of the Raptor Egg Yolk. Nigel
W.H. Barton, Nicholas C. Fox, Peter F. Surai, and Brian K. Speake 33
Preliminary Ground and Aerial Surveys for Orange-breasted Falcons in Central
America. Russell Thorstrom, Richard Watson, Aaron Baker, Serena Ayers, and David L. Anderson 39
Dispersing Vulture Roosts on Communication Towers. Michael l. Avery, John s,
Humphrey, Eric A. Tillman, Kimberly O. Phares, and Jane E. Hatcher 45
Raptor Abundance and Habitat Use in a Highly-Disturbed-Forest Landscape in
Western Uganda. Nathaniel E. Seavy and Christine K. Apodaca 51
Trophic Niche of North American Great Horned Owix. Lee a. Cromrich, Denver w.
Holt, and Shawne M. Leasure 58
Short Communications
Social Organization of a Trio Of Bearded Vultures ( Gypaetus barbatus) : Sexual and Parental
Roles. Joan Bertran and Antoni Margalida 66
Genetic Evidence of Ali.oparental Care of a Female Lesser Kestrei. in an Alien Nest. Pedro J.
Cordero, Jose M. Aparicio, and David T. Parkin 70
NE.STING OF Long-eared Owls Along the Lower Big Lost River, Idaho: A Comparison of 1975-76
and 1996-97. Natalie A. Fahler and Lester D. Flake 73
Behavioral and Ph\sical Development of a Nestling Crested Eagle {Morphnus GuiANENsrs)
.
David
F. Whitacre, Juventino Lopez Avila, and Gregorio Lopez Avila 77
Spring Weather and Breeding Success of the Eurasian Kestrel {Falco riNNUNCULUs) in Urban
Rome, Italy. Luca Salvati 81
Eatal Caryospora Infection in a Free-living Juvenile Eurasian Kestrel {Falco riNmmcuLus) .Olivei:
Krone 84
Book Review. Edited by Jeffrey S. Marks 87
Manuscript Referees 89
Number 2
An Urban Osprey Population Established by Translocation. Mark s. Marteii, Judy
Voigt Englund, and Harrison B. Tordoff 91
Breeding Grounds, Winter Ranges, and Migratory Routes of Raptors in the
Mountain West. Stephen W. Hoffman, Jeff P. Smith, and Timothy D. Meehan 97
Circuitous Autumn Migration in the Short-toed Eagle( Circaetus gallicus) .
Nicolantonio Agostini, Luca Baghino, Charles Coleiro, Ferdinando Corbi, and Guido Premuda Ill
Spring Migration of Adult and Immature Buzzards {Buteo buteo) through Elat,
Israel: Timing and Body Size. Reuven Yosef, Piotr Tryjanowski, and Keith L. Bildstein 115
Provisioning Rates and Time Budgets of Adult and Nestling Bald Eagles
AT Inland Wisconsin Nests. D. Keith Wamke, David E. Andersen, Cheryl R. Dykstra,
Michael W. Meyer, and William H. Karasov 121
A Line Transect Survey of Wintering Raptors in the Western Po Plain of
Northern Italy. Giovanni Boano and Roberto Toffoli 128
Short Communications
Bald Eagle Reproductive Performance Following Video Camera Placement. Cheryl R. Dykstra,
Michael W. Meyer, and D. Keith Warnke 136
Absence of Bi.ood Parasites in Nestlings of the Eleonora’s Falcon {Falco ejmonoraf). Alejandro
Martinez-Abram and Gerardo Urios 139
Possible Choking Mortalities of Adult Northern Goshawks. Thomas D. Bloxton, Andi Rogers,
Michael F. Ingraldi, Steve Rosenstock, John M. Marzluff, and Sean P. Finn 141
Exhumation of Food by Turkey Vulture. Harvey R. Smith, Richard M. DeGraaf, and Richard S.
Miller 144
Bats as Prey of Barn Owls ( lYro alba) in a Tropical Savanna in Bolivia. Julieta Vargas, Carlos
Landaeta A., and Javier A. Simonetti 146
Food of the Lesser Kestrel (Falco naumanni) in its Winter Quarters in South Africa. Grzegorz
Kopij 148
Red-shouldered Hawk Feeds on Carrion. Bill Pranty 152
Letters
First Repiacement Clutch by a Polvandrous Trio of Bearded Vultures (Gypaetus baebatus) in the
Spanish Pyrenees. Antoni Margalida and Joan Bertran 154
Mississippi Kites Use Swallow-tailed Kite Nests. Jennifer O. Coulson 155
Erratum 157
Number 3
Population Status of Breeding Bald Eagles in Washington at the end of the
20th Century. James W. Watson, Derek Stinson, Kelly R. McAllister, and Thomas E. Owens 161
Response Distance of Ferruginous Pygmy-Owls to Broadcasted Conspecific
Calls. Glenn a. Proudfoot, Sam L. Beasom, Felipe Chavez-Ramirez, and Jody L. Mays 170
POST-FLEDGING SURVIVAL AND DISPERSAL OF PEREGRINE FALCONS DURING A RESTORATION
Project. LarkinA. Powell, DanJ. Calvert, Irene M. Barry, and Lowell Washburn 176
Morphology, Genetics, and the Value of Voucher Specimens: An Example with
CATT/ARTES Vultures. Carole S. Griffiths andJohn M. Bates 183
Oral Administration of Tiletamine/Zolazepam for the Immobilization of the
Common Buzzard {BUTEO BUTEO) . Martinjanovsky, Thomas Ruf, and Wolfgang Zenker 188
Hunting Behavior of and Space Use by Eastern Screech-Owls during the
Breeding Season. Jennifer E. Buhay and Gary Ritchison 194
Short Communications
ScHizocHROMiSM IN A PEREGRINE Falcon erom ARIZONA. David H. Ellis, Lynn W. Oliphant, and James
K. Fackler 200
Natal Dispersal of the Crested Caracara (Caracara cherjway) in Florida. Nicole M. Nemeth and
Joan L. Morrison 203
Recent Records of Crowned Eagles {Harpyhaliaetus coronatus) from Argentina, 1981-2000.
M. Isabel Bellocq, Patricio Ramirez-Llorens, and Julieta Filloy 206
New Observations of the Peregrine Falcon {Falco peregrinus) in Peru. Marc Kery 213
DNA Polymorphisms in Boreai. Owls {Aegolius funereus) . Janne Beheim, Katrine Eldegard, Gro
Bj0rnstad, Mats Isaksson, Geir Sonerud, Olav Heie, and Helge Klungland 218
Post-fledging Movements and Foraging Habitats of Immature White-tailed Sea Eagi.es in the
Nemuro Region, Hokkaido, Japan. Saiko Shiraki 220
Habitat Preferences, Breeding Success, and Diet of the Barn Owl (Tyto alba) in Rome; Urban
versus Rural Territories. Luca Salvati, Lamberto Ranazzi, and Alberto Manganaro 224
Incidence of Naturally-healed Fractures in the Pectoral Bones of North American Accipiters.
Aaron J. Roth, Gwilym S. Jones, and Thomas W. French 229
Piasma Chemistry Reference Values in Free-living Bonelli’s Fagle (Hieraaetus fasciatus)
Nestlings. Javier Balbontin and Miguel Ferrer 231
Letters
The Fox Kestrel {Falco alopex) Hoytrs. Tiziano Londei 236
Probable Breeding of Short-eared Owls in Southern West Virginia. Frank K. Ammer and Petra
Bohall Wood 237
Endangered Egyptian Vulture {Neophron percnopierus) Entangled in Powerline Ground-wire Stabilizer.
Laura Gangoso and Cesar J. Palacios 238
Barred Forest-Falcon {Miciustur ruficollis) Predation on a Hummingbird. Tony Nunnery and
Mark R. Welford 239
Book Reviews. Edited byjeffrey S. Marks 241
Number 4
Foraging Ecology of Nesting Bald Eagles in Arizona, w. Grainger Hunt, Ronald e.
Jackman, Daniel E. Driscoll, and Edward W. Bianchi 245
Vernal Migration of Bai.d Eagles from a Southern Colorado Wintering Area.
Alan R. Harmata 256
Does Northern Goshawk Breeding Occupancy Vary with Nest-stand Character-
istics on the Olympic PeNINSUIA, Washington? Sean P. Finn, Daniel E. Varland, and
John M. Marzluff 265
Subordinate Males Sire Offspring in Madagascar Fish-Eagle {Haliaeetus vociee-
ROWES) POLYVNDROUS BREEDING GROUPS. Ruth E. Tingay, Melanie Culver, Eric M.
Hallerman, James D. Fraser, and Richard T. Watson 280
Nesting and Perching Habitat Use of the Madagascar Fish-Eagle. James Berkeiman,
James D. Fraser, and Richard T. Watson 287
Use of Vegetative Structure by Powerful Owls in Outer Urban Melbourne,
Victoria, Austraija—Implications for Management. Rayiene Cooke, Robert WaiUs,
andJohn White 294
Nest-Site Selection of the Crowned Hawk-Eagle in the Eorests of Kwazulu-
NATAL, South Africa, and TAI, Ivory Coast. Gerard Malan and Susanne Shultz 300
Short Communications
Juvenile Dispersal of Madagascar Fish-Eagles Tracked by Satellite Telemetry. Simon
Rafanomezantsoa, Richard T. Watson, and Russell Thorstrom 309
Prey OF the Peregrine Falcon {Falco Peregrinus cassini) in Southern Argentina and Chile. David
H. Ellis, Beth Ann Sabo, James K. Fackler, and Brian A. Millsap 315
An Elevated Net Assembly to Capture Nesting Raptors. Eugene A. Jacobs and Glenn A. Proudfoot 320
Florida Bald Eagle {Haliaeetus teucocephalus) Egg Characteristics. M. Alan Jenkins, Steve K.
Sherrod, David A. Wiedenfeld, and Donald H. Wolfe, Jr. 324
Osprey Ecology IN THE Mangroves OF Southeastern Brazil. Robson Silva e Silva, Fabio Olmos .... 328
Diet of Breeding Tropical Screech-Owls ( Otus choliba) in Southeastern Brazil. Jose Carlos
Motta-Junior 332
Letters
Comments of the First Nesting Record of the Nest of a Slaty-backed Forest Falcon {Micrastur
MIRANDOLLEI) IN THE ECUADORIAN AMAZON. Russell Thorstrom 335
Micrastur or Accipiter, That is the Question. Tjitte de Vries and Cristian Melo
Book Reviews. Edited by Jeffery S. Marks
Information For Contributors
337
338
340
Index to Volume 36 344
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2003 ANNUAL MEETING
The Raptor Research Foundation, Inc. 2003 annual meeting will be held on 3-7 September 2003in Anchorage, Alaska. For information about the meeting see the following website: http://www.alaskabird.org or contact Nancy DeWitt ([email protected])
.
Persons interested in predatory birds are invited to join The Raptor Research Foundation, Inc. Sendinquests for information concerning membership, subscriptions, special publications, or change of address
to OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A.
TheJournal ofRaptor Research (ISSN 0892-1016) is published quarterly and available to individuals for $33.00per year and to libraries and institutions for $50.00 per year from The Raptor Research Foundation, Inc., 14377117th Street South, Hastings, Minnesota 55033, U.S.A. (Add $3 for destinations outside of the continental UnitedStates.) Periodicals postage paid at Hastings, Minnesota, and additional mailing offices. POSTMASTER: Sendaddress changes to TheJournal ofRaptor Research, OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A.
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Raptor Research Foundation, Inc., Awards
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The Tom Cade Award recognizes an individual who has made significant advances in the area of captive prop-
agation and reintroduction of raptors. Nomination packets can be submitted at any time. Contact: Brian
Walton, Predatory Bird Research Group, Long Marine Laboratory, University of California, Santa Cruz, CA95064 U.S.A.; tel. 408-459-2466; e-mail: [email protected].
The Fran and Frederick Hamerstrom Award recognizes an individual who has contributed significandy to the
understanding of raptor ecology and natural history. Nomination packets can be submitted at any time. Con-
tact: Dr. Clint Bo<il, Texas Cooperative Fish and Wildlife Research Unit, BRD/USGS, Texas Tech University,
15th Street & Boston, Ag Science Bldg., Room 218, Lubbock TX 79409-2120 U.S.A.; tel. (806) 742-2851;
e-mail: [email protected].
Student Recognition and Travel Assistance Awards
The James R. Koplin Travel Award is given to a student who is the senior author and presenter of a paper or
poster to be presented at the RRF annual meeting for which travel funds are requested. Contact; Dr. Patricia
A. Hall, 5937 E. Abbey Rd. Flagstaff, AZ 86004 U.S.A.; tel. 520-526-6222; e-mail: [email protected].
Application Deadline: due date for meeting abstract.
The William C. Andersen Memorial Award is given to the students who are senior authors and presenters of the
best student oral and poster presentation at the annual RRF meeting. Contact: Laurie Goodrich, HawkMountain Sanctuary, 1700 Hawk Mountain Road, Kempton, PA 19529 U.S.A.; tel. 610-756-6961; email;
[email protected]. Application Deadline: due date for meeting abstract; no special application
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Grants
For each of the following grants, complete applications must be submitted to the contact person indicated by
15 February. Recipients will be notified by 15 April.
The Dean Amadon Grant for $200-400 is designed to assist persons working in the area of distribution and sys-
tematics (taxonomy) of raptors. Contact: Dr. Carole Griffiths, 251 Martling Ave., Tarrytown, NY 10591
U.S.A.; tel. 914-631-2911; e-mail: [email protected].
The Stephen R. Tully Memorial Grant for $500 is given to support research, management, and conservation of
raptors, especially to students and amateurs with limited access to alternative funding. Contact; Dr. KimTitus, Alaska Department of Fish and Game, Division of Wildlife Conservation, P.O. Box 240020, Douglas,
AK 99824 U.S.A; e-mail; [email protected].
The Leslie Brown Memorial Grant for up to $1,000 to support research and/or dissemination of information
on birds of prey, especially to proposals concerning African raptors. Contact: Dr. Jeffrey L. Lincer, 9251
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