Post on 07-Oct-2020
Co-Authors
Doug Howell, Waterfowl Biologist
North Carolina Wildlife Resources Commission
Wildlife Management Division
Surveys and Research Program
Joe Fuller, Migratory Game Bird Coordinator
North Carolina Wildlife Resources Commission
Wildlife Management Division
Surveys and Research Program
Roald Stander, M.S. Student
University of Manitoba
Department of Environment and Geography
Master of Environment Program
Special Thanks! – You are viewing this document because you have played an integral role in insuring
this project’s successful fruition. Whether you are a property owner, research advisor, local wildlife
professional, project sponsor, or simply a helping hand, your help does not go unnoticed. I would like
to thank every person involved.
- Daniel Lawson
Graduate Research Assistant
Lawson 1
Background
The American black duck (Anas rupripes) population has been in decline since the 1950s. According to United States Fish and Wildlife Service (USFWS) mid-winter survey estimates, black duck numbers decreased more than 50% from the 1950s to the 1990s (Figure 1) (USFWS 2017). Since this time, the black duck population has stabilized in the Atlantic Flyway (Figure 2).
Figure 2: USFWS Mid-winter Waterfowl Survey Estimates for the American Black Duck in the Atlantic Flyway (1990-2015)
There are several potential explanations for
this decline, including loss in the quantity and
quality of breeding and wintering habitats,
overharvest, and interactions (competition,
hybridization) with mallards (Anas
platyrhynchos) during the breeding and
wintering periods (Anderson et al. 1987, Conroy
et al. 2002). The historical loss of coastal
wetlands in the Mid-Atlantic region has been
significant (Dahl 1990) and their continued
degradation (Tiner 1987, Dahl 2000, Dahl 2006,
Stedman and Dahl 2008, Dahl and Stedman
2013) may limit the ability of this area to support
black duck populations at conservation goals
(Morton et al. 1998, NAWMP 2014).
Although there have been ongoing efforts to
understand the limiting factors of Mid-Atlantic
black ducks during the nonbreeding season
(Cramer et al. 2012, Livolsi 2015, Ringelman et al.
2015), there is a need to better understand the
breeding season limiting factors as well,
especially in light of analyses that suggest long-
term declines in recruitment (Brook 2006).
Consequently, the Black Duck Joint Venture has
determined that there is a need to quantify
regional differences and factors influencing
black duck productivity.
Black ducks breed in highest concentrations in
the eastern Canadian provinces (Rusch et al.
1989), and nesting studies in this region
generally have found nest success is adequate to
maintain the population and is similar to
sympatric mallards (Petrie et al. 2000). A smaller
population of black ducks nest in the Mid-
Atlantic region, however less is known about
their nest success. Until recently, the status of
the breeding black duck population in North
Carolina was poorly understood. North Carolina
represents the southern extent of the species’
breeding range (Stewart 1958, Parnell & Quay
1962, Bellrose 1980). Although breeding black
ducks in North Carolina are well documented,
their long-term population trend and nesting
success is unknown. We suspect that breeding
populations have declined over time, similar to
breeding populations farther north in Virginia
and Maryland (Costanzo and Hindman 2007),
Figure 1: USFWS Mid-winter Waterfowl Survey Estimates for the American Black duck in the Atlantic and Mississippi Flyways (1955-2015)
Mid-winter Survey for American Black Ducks (1955-2015)
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but there is no empirical or baseline data to
support this.
There have been a few past attempts to
quantify the status of breeding black ducks in
North Carolina; however, these were spatially
limited. Parnell and Quay (1962) reported black
duck production between 1938-1958 on Pea
Island, North Carolina and conducted more
thorough nest searching and nest success
research in 1959-1960. They found black duck
nesting was beginning to decline and noticed
lower apparent nest success (69%) than those
observed in the Chesapeake Bay (91%) or
Canada (81%) (Stotts 1956, Wright 1954).
Additional research in 1990 (Fleming et al. 2000)
on Piney Island, North Carolina located 12 nests
with an apparent nest success of only 67%. In
2013, the North Carolina Wildlife Resources
Commission (NCWRC) initiated an aerial black
duck population survey to better understand the
distribution and density of breeding black ducks
in suitable coastal marsh habitat in North
Carolina (NCWRC unpublished data). This survey
is based upon the Atlantic Flyway Breeding
Waterfowl Plot Survey (AFPS; Heusmann and
Sauer 2000). During 2013-2016, the
methodology and survey area was refined to
produce more precise breeding population
estimates. In 2016, the sampling frame
contained 1,267 1-km² plots containing between
5-40% marsh habitat, and 595 plots containing
>40% marsh habitat which was deemed suitable
for nesting black ducks. Of these plots, a
randomly sampled subset of 134 plots was
surveyed via helicopter. Extrapolating the results
of the survey of this subset of plots to the
entirety of North Carolina coastal marsh habitat,
results in an estimate of 2,404 (90% CI = 1,131-
3,678) total black ducks and 694 (90% CI = 500-
888) nesting pairs. However, there is no
knowledge about their nest success and the
factors that could influence those values.
Proposed Research
As per research objective request from the
Black Duck Joint Venture, NCWRC along with the
University of Delaware Department of
Entomology and Wildlife Ecology (UDel) initiated
a project that would quantify the breeding effort
of the American black duck in coastal North
Carolina. Specifically, it is our (NCWRC and UDel)
goal to estimate reproductive parameters of
breeding black ducks in coastal habitat in North
Carolina as a function of nesting habitat quality,
human disturbance, predation, flooding, and
marsh burning.
Breeding Black Duck Survey 2017
Introduction: The North Carolina Wildlife
Resources Commission Breeding Black Duck
Survey conducted in 2017 is built upon surveys
conducted each year since 2013. Since the pilot
survey in 2013, NCWRC has developed a method
to index the breeding black duck population in
suitable coastal marsh habitat in North Carolina.
Results: This year 131 of 135 randomly chosen
1-km² plots were surveyed in three days, April 9-
11, 2017. Three were not surveyed due to
restricted airspace at the Dare County Bombing
Range and one plot could not be surveyed due to
residential development. The survey team
counted 158 total black ducks. Per Atlantic
Flyway Plot Survey (AFPS) protocols, this
represented 75 indicated pairs (IP) (Table 1).
Table 1: Group Size of Observed Black Ducks, April 2017.
Group Size Number of Observations 1 29
2 36
3 3
≥4 3
Mean counts of indicated pairs (IP's) of black
ducks were highest in plots containing >40%
marsh. However, plots containing 5-40% marsh
contributed 44% of the total IP estimate due to
the large number of plots in this survey stratum.
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The total population estimate included 1,048 IP's
and 2,270 total indicated birds (TIB) (Table 2).
Table 2: Population estimates of black ducks by survey strata in coastal North Carolina, April 2017.
Discussion: This survey represents the 5th year
of a multi-year effort to develop an aerial survey
to estimate the size of the breeding black duck
population in suitable coastal marsh habitat in
North Carolina. Since no changes were made to
the survey design in 2017, only results from 2016
and 2017 surveys are directly comparable.
Although the estimate of IP's increased
considerably from 2016, the 90% confidence
intervals overlap, suggesting that increases may
in part be related to sampling error.
Interestingly, TIB's in 2017 was very similar to
2016. Total indicated birds is influenced by
observations of grouped black ducks (>4
observed). Grouped black ducks may represent
migrant black ducks that have not left the state
or local, nonbreeding birds (during the survey
window). Previous modifications to survey
design have been made with the goal of reducing
standard errors of survey estimates. Due to
three plots having an outlier number of IP's
observed, standard error increased considerably
from 2016 (SE=110) to 2017 (SE=205). Moving
forward, there is likely no way around this issue
apart from adding additional survey plots.
The inability to determine the sex of any
observed black ducks from the air introduces
some bias into the estimate of IP’s and TIB’s. Per
AFPS protocols, a conservative approach was
used when recording groups of black ducks of
unknown sex. The inability to distinguish the sex
of black ducks has the potential to influence IP
estimates, both positively and negatively. For
example, groups of three black ducks were
treated as two IP’s. If these three black ducks
were identified as three drakes, they would have
been treated as three IP’s. Alternatively,
observations of single black ducks were counted
as one IP. However, some portion of the single
black ducks observed were likely hens disturbed
from their nest. In 2017, the survey team was
able to positively identify one hen flushing from
a nest and did not include this observation as an
IP.
NC American Black Duck Nesting Study
Introduction: The North Carolina Wildlife
Resources Commission and the UDel coordinate
the American black duck breeding ecology study.
This year we conducted nest searches for
incubating black ducks on six 100 m2 study sites
in coastal North Carolina. We monitored these
nests at seven-day intervals until they were
terminated (hatched, depredated, flooded, etc.).
Vegetation measurements were then taken at
nest termination. A select number of nests were
additionally monitored via trail camera in hopes
to better record causes of nest failure and to
synthesize an incubation break chronology for
black ducks in the southern Atlantic Flyway.
Further, we collaborated with Delta Waterfowl
Foundation to test the efficacy of nest searching
with aerial drones employing thermal imaging
cameras.
Stratum No. of Plots Surveyed
Total No. of Plots
Total Indicated Pairs/ Plot
Estimated Indicated Pairs
Estimated Total Indicated Birds
Plots with >40% Marsh 44 595 0.98 581 (293-870) 1,163 (586-1,740)
Plots with 5%-40% Marsh 88 1,267 0.37 466 (251-681) 1,107 (574-1,639)
Total Survey Area 131 1,862 - 1,048 (706-1,389) 2,270 (1,520-3,019)
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Nest Searching: Although there have been a few
previous attempts to quantify the breeding
status of black ducks in coastal North Carolina
(Parnell & Quay 1962, Fleming et al. 2000), there
were not any datasets available that identified
optimal black duck nesting habitat in this region.
To determine how and where to search for these
nests, we drew from studies conducted farther
north, in the Chesapeake Bay region (Krementz
1991, Costanzo and Hindman 2007, Haramis
1996, Stotts and Davis 1960). Based on our
findings, we decided to focus on three habitat
types: upland buffers (upland habitat that
borders wetlands), islands, and tidal brackish
marsh. Further, we chose six focal areas that
contained these habitats and, per the NCWRC
breeding black duck surveys, breeding black
duck pairs. For the sake of logistics, we placed
four sites northeast of the Pamlico River mouth
along the inner banks of the Pamlico Sound
stretching to the intersection of US 64 and the
Croatan Sound (Figure 3). We placed two study
sites encompassing parts of Pea Island and
Roanoke Island on the Outer Banks of North
Carolina (Figure 4).
Figure 3: Inner Banks Study Sites. Hyde and Dare Counties, North Carolina
Figure 4: Outer Banks Study Sites. Dare County, North Carolina
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Our nest searching technique was modified
from all-terrain vehicle (atv) chain drags used for
locating upland nesting waterfowl (Klett et. al.
1986), where a chain suspended between two
atvs is pulled across standing vegetation. The
chain covers all vegetation in between the atvs
and chain links rattle to produce a metallic sound
that causes nesting hens to flush as the atvs
progress forward. Since our study sites were not
accessible to atvs, we decided to modify the
dragging apparatus so it could be used by two
technicians on foot. Nylon rope seemed to be
the most sensible alternative. We used 100 ft.
lengths of rope and attached aluminum cans
spaced at ~2m intervals along the entire length
of the rope. Every can received small (~3-4 cm)
rocks to serve as noisemakers in lieu of shifting
chain links. Two technicians conducted nest
drags. One technician would stretch the rope to
the edge of a wetland, typically on the edge of a
body of water. The other technician would
stretch the other end of the rope directly inland
from the wetland edge. Once the rope was
extended, both technicians traveled forward
while remaining parallel to one another and the
wetland edge (Figure 5). An additional technician
was used as a spotter that constantly watched
the dragline to identify flushing hens. The
spotter would identify the exact location of the
flushing hen and guide the other technicians to
the nest. Technicians continued forward until a
hen was flushed. Once a hen was flushed, one
technician would approach the nest and begin
data collection while the other stayed at least 5
meters away and recorded data. In areas where
we could not drag the rope due to vegetation
height and rigidity, technicians distanced
themselves 5–25m apart and walked transects of
the selected area. We utilized this technique
specifically on spoil islands in the Pea and
Roanoke Island study sites (Figure 4).
Figure 5: Nest Dragging in North Carolina Brackish Marsh
We initiated nest searching on April 1ST and
continued until June 17th. During that time we
found our nest dragging technique to be a great
success and almost necessary to find the
sparsely positioned black duck nests in the many
thousands of acres of coastal salt marsh that
were surveyed. This season we found and
monitored a total of 56 duck nests. The majority
of nests were black duck (n=47, 84%). Mallard
and gadwall (Mareca strepera) made up the
remaining nests at 4 (7%) and 5 (9%),
respectively (Figure 6).
Figure 6: 2017 Nests Species Composition
The inner banks study areas (Figure 3)
contained mostly brackish marsh and upland
buffer habitat. We found 55% (n=31) of the
nests in these areas. The remaining 45% of nests
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(n=25) came from the island habitats of the
outer banks.
American black ducks favored nesting on the
slightly elevated beach ridges of the inner banks’
brackish marsh. Beach ridges were slightly
higher than the adjacent low marsh because of
sand deposition due to years of wave action.
These ridges were directly adjacent to the open
water of back bays and points jutting into the
sound. The dominant plant species on the
brackish marsh beach ridges (high marsh) were:
black needlerush (Juncus roemerianus), salt-
marsh cord grass (Spartina alterniflora), salt-
meadow cord grass (Spartina patens), and
saltgrass (Distichlis spicata). These species made
up the high marsh, with each species dominating
in patches or zones to form a mosaic vegetation
pattern (Figures 7 - 8).
Figure 7: Brackish High Marsh Mosaic
Figure 8: High Marsh Dominated by Spartina patens
On our two Outer Banks study sites (Roanoke
Island and Pea Island) we spent a great majority
of our time searching natural and man-made
islands within the Pamlico Sound. These islands
proved to be very diverse in topography,
vegetation structure and composition, and black
duck nesting productivity. Topography reflected
how the island was formed, whereas vegetation
structure and productivity reflected how long
ago. Man-made (dredge islands) where typically
elevated and contained an array of plant
communities (Figures 9 - 10). Some of which
were: dune grasslands, maritime shrublands,
upper and lower beach, and maritime vine
tangles. Typically, the older the island, the later
the successional stage. Naturally formed islands
were low lying and were broadly classified as
brackish marsh. As mentioned earlier, each
island had unique black duck nesting
productivity. Most of the variability was
attributed to predator influence and vegetation
structure.
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Figure 9: Man-made Dredge Island > 10 Years Old
Figure 10: Man-made Dredge Island < 10 Years Old
Collectively, nests were located an average of
25.6 meters from open water. Nests located in
flood prone spots, brackish marsh especially,
were slightly elevated (15-30 cm) structures that
consisted of needlerush or Spartina spp. leaves
(Figure 11) and resembled overwater-nesting
diving duck nests. Nests in the brackish marsh
that were not elevated, were tucked deep into
surrounding cover (Spartina patens, Distichlis
spicata, and Juncus roemerianus) and the bowl
was low in profile and mainly constructed of
Spartina patens (Figure 12). Both varieties had
down lining the nest bowl, but a profuse lining
seemed to be less common in elevated
structures.
Figure 11: Elevated Black Duck Nest in Brackish Marsh
Figure 12: Low-Profile Black Duck Nest in Brackish Marsh
On islands in the Outer Banks study sites, black
duck nests were located within dense vegetation
in any combination of warm season grasses,
Rubus, and forbs (Figures 13 - 14).
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Figure 13: Black Duck Nest in Pioneer Island Vegetation
Figure 14: Black Duck Nest in Dense Island Vegetation
We took vegetation measurements at nest
sites once nests were fated (e.g. abandoned,
depredated, etc.). We hoped to get an idea of
the exact microhabitat black ducks chose for
nesting in North Carolina. To achieve this,
technicians collected percent composition with a
Daubenmire frame and Visual Obstruction
Readings (VOR’s) with a Robel pole (Robel et al.
1970). Along with the VOR’s, we recorded
maximum average vegetation height. We found
percent composition at the microhabitat scale to
be; 65% grass, 14% litter, 7% forbs, 5% woody
vegetation, 5% water, and 4% bare soil. Our
average VOR was 0.5 meters meaning there was
more than 50% visual coverage by vegetation
below that height. Finally, max average
vegetation height yielded 0.9 meters.
Earliest and latest nesting initiation, peak(s) of
nesting initiation, and nesting season duration
are questions that have never been confidently
answered of black ducks nesting in coastal North
Carolina. Foremost, we estimated nesting
initiation questions by backdating to the
initiation date (the day the first egg was laid).
We did this by adding the number of eggs in the
nest to the incubation stage in days, and then
took the sum and subtracted it from the date we
discovered the nest. Nesting season was simply
the date the first nest of the season was initiated
until the final nest was terminated. The earliest
date we found black ducks initiating nests was
March 3; the latest date was May 24 (Figure 15).
This year we noticed two separate nest initiation
peaks. The first was during the first two weeks of
April (4/2 - 4/15). The second peak was over the
first two weeks of May (4/30 – 5/13). One
possible explanation for the separate peaks is an
inclement weather event that occurred in mid-
late April. During this time, several flood events
caused a high rate of nest failure in brackish
marsh adjacent to the Pamlico Sound. A few of
our monitored nests remained under water for
an extended period of time. It is possible that
the peak at the beginning of May could have
been a renesting effort.
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Figure 15: 2017 Black Duck Nest Initiation Chronology
Nest Monitoring: This season we monitored 47 black duck nests at 7-10 day intervals (Klett et al. 1986). The product of our monitoring efforts allowed us to have several exposure days to insure that our incubation stage estimates were accurate. Multiple visits also insured more precise nest fates, because it reduced the time terminated nests were exposed to the elements. The composition of nest fates for the 2017 season are as follows in (Table 3).
Table 3: 2017 Nest Fate Composition
We identified hatched nests according to (Klett
et al. 1986). In the nest, we looked for presence
of detached shell membranes and yellowish
feather sheaths or small egg fragments without
membranes in nest material, or presence of
ducklings in the nest bowl. Identifying
abandoned nests was a little bit trickier. On
initial nest visits, we noted the hen status as it
related to the nest (i.e. hen present, eggs warm
and covered, eggs cold and uncovered, etc.).
Along with collecting this data, we covered the
nest with down and other present nest bowl
materials and then made a distinct “X” on top
with two pieces of contrasting vegetation.
Likewise, we used the progression of embryo
development to determine if the hen was still
actively incubating the nest. There were several
factors we identified that caused hens to
abandon nests. (Figure 16).
Figure 16: 2017 Nest Abandonment Causes
The factor that attributed most to nest
abandonment was unfortunately, our own initial
Fate Black Duck Nests
Hatch 9
Abandoned 21
Depredated 12
Nonviable 3
Unknown 2
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activity at the nest site. Of this percentage, all
nests were still in lay or very early in incubation
(< 7days). Of the twelve depredated nests, we
identified several nest predators. Nest predators
identified included American and fish crow
(Corvus brachyrhynchos and Corvus ossifragus,
respectively), bald eagle (Haliaeetus
leucocephalus), raccoon (Procyon lotor),
American mink (Neovison vison), and red
imported fire ant (Solenopsis invicta). Nonviable
nests were nests where all eggs addled before
any other fate. To aid in fating nests, we placed
trail cameras on 35 black duck nests.
Trail Cameras: Placing trail cameras on nests
helped us to understand the nesting ecology of
the black duck in North Carolina. By formatting
cameras to capture images every minute, we
were able to record the frequency and duration
of incubation breaks. Cameras captured many
events that had an impact on the nest fate.
Some of these events included: flooding,
depredation, prolonged incubation breaks, and
abandonment. Sample trail camera photos are
pictured in (Figures 17-20).
Figure 17: April 25 Flooding Event with Submerged Black Duck Nest Pictured in Top-center
Figure 18: Black Duck Hen Elevating Nest Bowl Prior to High-water Event
Figure 19: Bald Eagle Depredation
Figure 20: Raccoon Depredation
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Collaborative Drone Research
Figure 21: Delta Waterfowl Research Drone
Introduction: This year we had the opportunity
to collaborate with Delta Waterfowl Foundation
and the University of Manitoba on research
testing the efficacy of thermal-imagery equipped
drones in avian nest searching. Due to the
sparseness of black duck nests within the
brackish marsh of coastal North Carolina, we saw
this as an opportunity to increase our nest
searching capacity while contributing to drone-
based wildlife sampling research. Roald Stander,
the drone research graduate student with
University of Manitoba, brought his research to
our study sites May 24-30.
Results: We chose study plots 10 – 40 acres in
size that contained known active black duck
nests. We surveyed sites between midnight and
sunrise. Detectability of the thermal targets by
the thermal camera varied from site to site; on
the same site over multiple days; or even on the
same site during a single survey. Different
habitats had certain physical characteristics
which increased/decreased the likelihood of
detecting the targets. Certain meteorological
conditions seemed to greatly influence
detectability. Humidity ultimately negatively
influenced detectability. Thermal reflectance
from moonlight was also observed.
Our goal was to fly three successional missions
over different nights recording coordinates of
each target. The aim of flying multiple times
over the same area was to rule out transient
birds, in that targets observed three nights in a
row would be indicative a nesting bird. Flying
three nights was not achieved at all sites due to
inclement weather. All of the sites that we
visited had a relatively low number of known
nests.
The thermal camera does not detect heat
signatures, but rather detects relative
temperature differences. When the habitat
being surveyed is of a homogenous
temperature, detectability is very high. The
avian thermal targets are the hottest objects
within the field of view (FOV) of the camera and
typically show up clearly.
Discussion: Surveying coastal regions provides
unique challenges due to the humid
conditions. Black ducks in the region typically
select salt marsh hay grass (Spartina patens) as
nesting cover. The structure of the grass seems
to inherently hold moisture due to the c-shaped
structure of the blade. The high levels of low-
lying humidity seems to be exacerbated by the
fact that this is a tidal area.
Despite all the challenges, we located 2/2
known black duck nests and 14 Clapper rail
nests. The known nests were relatively open
from above, and the rail nests were located in
black needlerush. One of the two active black
duck nests included in the survey was extremely
visible from 150 meters (Figure 22) using a
transect-based survey method. We were able to
hover over the nest at a relatively low height, <5
meters, without causing the hen to flush (Figure
24).
We noticed a raccoon momentarily disappear
as it was moving through matted patches of
vegetation, including Spartina patens. This
prompted us to test the detectability of a hot
thermal target (>60⁰C) placed in typical nesting
cover. The thermal camera could only detect
the target at 7’ AGL.
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The habitat inherently had challenges
associated with working in tidal areas. The
observed detectability warrants further testing.
Although we found all known nests, the results
were inconclusive.
Figure 22: Nesting Black Duck Thermal Imaging Snapshot
from 150 meters
Figure 23: Nesting Black Duck Thermal Imaging Snapshot
from 50 meters
Figure 23: Nesting Black Duck Thermal Imaging Snapshot
from <5 meters
Lawson 13
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