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HUMAN DISTURBANCE OF SIERRA NEVADA BIGHORN SHEEP

.ORIN L. HICKS,1 School of Natural Resources, University of Michigan, Ann Arbor, Ml 48109 ;AMES M. ELDER,: School of Natural Resources, UniVersity of Michigan, Ann Arbor, Ml 48109

\bstract: California bighorn sheep (Ovis canadensis californiana) and recreationists were studied in the ~!err.l :\evada ~Iountains of California from :..·lay through August 1976. Direct observation of sh~ep ~nd :'t'ople, pellet transects, and hiker interviews were used to assess overlap in areas of use an~ nature of ::1teractions. Distance, juxtaposition, age and sex composition, and herd size are importar.r faLcors in ·eaction of bighorns to humans. ~1eadows used by humans were inherently poor meadows for bighorn .heep, based on vegetation analysis. Use of meadows by sheep was correlated wiih amount ~r preferred ::1ragc: species and vegetative cover. Hiker foot-trails did not affect sheep movements in the sP•:·mer range. !lighorn-human encounters were limited to specific locations and were not adversely affectin;g ilie bighorn ;'llpnlation. Nevertheless, regulations should continue to limit use of the study area by humans.

California bighorn sheep of the Sierra \enda l\<1ountains in California are the .'nly naturally occurring population of :his subspecies in the United States and were classified as 1are by the U.S. De­:mrtment of Interior (1966). Estimated ?opnlations declined from 390 in 1950 to !80 in 1972 due to a variety of suspected mflucnces (Jones 1950, NlcCuiiouzh and Schneegas 1966, Dunaway 197lb, Jor­gensen and Schaub 1972, \Veaver 1972).

Hansen (1971), \Voodward et al. (1974), Geist (1971:87-88, 1975), and others have described the impact of human ac·· tivities on populations of bighorn sheep. Dunaway (197lb) concluded that distur­bance by humans was the most important Cte:tor limiting populations of bighorns in the Sierra Nevada. Gaps between exist­ing herds were areas of high human use, .\ltd there was an a,:pparent correlation be­tween the recent increase in recreational .tctivity and the decline in bighorn num­bers. i-Iowever, little supporting data were available.

Acting on Dunaway's hypothesis, the U.S. Forest Service established the Cal----

1 Pn•sent address: Burlington Northern Re­'ourees Div., 700 South Ave. \Vest, ~lissoula, ~lT }~801.

2 Present address: 9430 Edward, Brighton, ~H i~liH.

J, \\ildl. ~1acmge. 43(4):1979

J. WILDL. MANAGE. 43(4):909-915

ifornia Bighorn Sheep Zoological Area in 1971. Regulations limited entrance to 25 hikers per day, and prohibited off-trail hiking and grazing of recreation and sad­dle stock (Dunaway 1971a).

The purposes of this study were to de­termine the amount of overlap in current use by humans and bighorns, the nature and extent of the interactions, and wheth­er the interactions have a deleterious ef­fect on the bighorns. The study extended from ~lay through August 1976, and co­incided with the peak periods of activity of both humans and sheep. .

The U.S. Forest Service and the Na~ tional Park Service provided.· financial s·upport. D. R .. McCullough and S. R. Tocher, University of Michigan, 'rovid-' ed guidance and assistance throughout the study. D. Garber (Forest Service) ar~d D. Parsons (Park Service) provided logis­tical support. \Ve thank J. \Vehausen for his assistance in formulating the study and participating in the fieldwork. G. Smith, J. Elder, S. Sherwood, D. Asay, and H. \V. Elliot, III also assisted in the fieldwork.

STUDY AREA AND METHODS

The 1It. Baxter herd area was chosen as the study site because it supports the largest herd of California bighorns in the

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910 DISTURBANCE OF BIGHOR,'l SHEEP • Hicks and Elder

Meadows Sampled:

1 Baxler lake 2 Oak Fork

I 1 Km I

3 Upper Summit Meadow 4 Lower Summit Meadow 5 Parker Lakes 6 Rae Lakes

> w ..J ..J

< >

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Fig. 1. The Mt. Saxter study area showing major topo­graphic features and the meadow sampling locations.

Sierra Nevada and receives considerable use by backpackers and packn·ains. The study area is dominated by a .steep east­em escarpment and grad'lal west slope (Fig. 1). Elevations exceed 3,900 m at :Nit. Baxter and drop on the east side to 1,500 m in Owens Valley. The crest is the boundary between Kings Canyon Nation­al Park to the west and Inyo National For­est to the east. The study area 1 ies within the John Muir Wilderness Area. Efforts were concentrated at Baxter Pass where encounters between bighorns and hu­mans were most frequent.

Bighorns and hikers on Baxter Pass were observed, with spotting scope and

binoculars, from a rock blind so that nei­ther was aware of the observers. Detailed activities of each bighorn band were summari..ed at 5-minute intervals (Alt­mann 1973). Location, movements, and behavior of bighorns and humans were recorded. When interactions between bighorns and humans were observed, a 5-point code system was used to classify reactions of the sheep: (0) Uncon.­cerned-feed, bed, and look occasional~ ly; (1) Curious-feed, bed, stand, and watch; (2) Concerned-feed, do not bed; (3) Immediate slow flight; and (4) Im­mediate fast flight.

Current use of meadows by bighorns was assessed at 2-week intervals by counting pellet groups on 4.5 X 30-m plots. Meadows \vere stratified into those with regular and no use by humans. Of the 6 meadows sampled (Fig. 1), Baxter Lake and Lower Summit meadows con .. tained trails and were classified as "hu­man-use, areas; Upper Summit, Parker Lakes, and Oak Fork meadows were deso ignated as "human non-usen meadows. An area not visited by hikers above the Rae Lakes was sl;)mpled as a human non­use meadow. Meadows were stratified in sloping and flat aspects, and pellet tran­sects were placed randomly within strata. Pe1rcent cover and species composition of vegetation on pellet transects were de­tennined for comparisons between loca­tions.

Two pellet transects were placed ad­jacent to the Baxter Pass trail to deter­mine its effect on sheep distribution. Both trail transects were 4.5 m wide and extended perpendicular to the trail on each side for a distance of60 m. The tran­sects were located in level areas at 3,700 min alpine zones on south-facing slopes. Trail pellet transects were sampled monthly.

\Vilderness users in the study area

J. \Vildl. Manage. 43{4)~1979

were interviewed trails daily UU.L.4AA,~

derness area, al activity, hiker sition, sheep en the presence of ence of dogs or trail activities.

Campsites search and tailed criterion space, trash provements was tive use code codes v ~ ·€ 0 to dicating heavy us

Peak-climbing mined by c;Ac:uu, ....... r

ters located on area and old brary collections.

RESULTS Including rep

observed. Most of ewes, lambs, higher elevations from 1 to 32 (x n1ained in open . .. escape terram, o forested areas, s areas of high h ewe ratio of 79: l indicated a good high reproductive marily to a mild creased neonatal

Baxter Pass, on portant summer majority of there. The area foraging, bedding, Sheep usually arri

J. ,Nild1. Manage.

blind so that nei­servers. Detailed orn band wen·

te intervals (Alt-tnovements, and

humans wen· ·ons behveen

were observed, a used to classify p: (0) Uncon­look occasional­bed, stand, ancl

......... ...,, ., do not bed; ight; and ( 4) I m-

ows by bighorns ek intervals by

s on 4.5 x 30-m d into those

se by humans. Of (Fig. 1), Baxter

t meadows con-cf; 1.ed as "hu­. Sufnmit, Parker

were des­m-use" meado\vs. hikers above the

d as a human non­were stratified in

and pellet tran­omlv within strata. ies ~omposition of

cts were de­between loca-

were placed ad-s trail to detcr­p distribution.

re 4.5 m wide and to the trail on

of 60 m. The tran-1 areas at 3,700

outh·facing slopes. ts were sampled

the study area

, ..-a ,')

~ ~e. 43(4):191.., . '

DISTURBANCE OF BIGHORN' SHEEP • Hicks and Elder 911

were interviewed at trailheads and along trails daily during July and August. In­terviews were informal, as 1 t,:ker to

er. Information was collected on l route, number of days in the wil-

erness area, camp locations, recreation­activity, hiker group size and compo-

. ition, sheep encounters, knowledge of presence of sheep in the a1rea, pres­

of dogs or stock animals, and off­activities.

Campsites were locatc'd by sy~t~matic and plotted Dn ah11hotos. A de­

ed criterion includir;.g fires, ~leeping trash accumulations, and site inl­ents was used to establish a rela­

ve use code for each campsite. The des were 0 to 4, with a score of 4 in­

heavy use. Peak-climbing activities were deter­

~., .. .u.ed by examining the check-in regis­located on major peaks in the study

""'"'""'" and old peak-climbing records in li­collections.

Including repetitions, 305 sheep were erved. 11ost of them were in groups ewes, lambs, and yearlirgs in the

. .-•••,t;.uer elevations. Group sizes ranged 1 to 32 (x = 7.2). Ewe groups re­

!ol'>"'"'uu.c;;d in open rocky habitat, close to terrain, but ram groups were in

orested areas, sometimes very close to areas of high human use. A lamb to adult

!bewe ratio of 79:100 (N = 63 adult ewes) ";-indicated a good 1976 lamb crop. This ~high reproductive success was due pri­t~arily to a mild winter in 1975 which in­,~ creased neonatal survival (Hicks 1977). .~ Baxter Pass, on the Sierra crest, was im-

.: portant sumn'l.er range for sheep, and a majority of bighorn sightings was made there. The area contained a mineral lick, foraging, bedding, and surveillance sites. Sheep usually arrived at the pass in late

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~J. Wildl. Manage. 43(4):1979

Table 1. Percentages of time spent by ewes, lambs, and yearlings on Baxter Pass, Sierra Nevada, based on 36 hours of observation during May-August 1976.

~Hdpoint of hour (PDT) Bt!d Feed !\love Stand

1100 6 26 61 7 1200 42 38 11 10 1300 43 19 28 10 1400 54 23 16 8 1500 27 38 25 10 1600 31 35 26 7 1700 21 60 10 9 1800 2 47 45 6

morning, and fed until late afternoon (Table 1). Bedding activity peaked in middle to late afternoon. As evening ap­proached, movement and feeding in­creased as sheep proceeded to night bed­ding sites .. Individual groups sometimes spent UP. to 6 hours a day on the pass and occasionally bedded there overnight.

Human Use of the Study Area In the Baxter Pass area, 39 groups of

hikers were interviewed. The mean group size was 4.0 hikers, and the mean trip length was 5.3 days. Of 35 groups questioned about off-trail use, 23 (66%) had engaged in some form, including peak-climbing and searching for big­horns.

Kings Canyon National Park records showed 2,675 overnight users in the Rae Lakes area during July and August. De­spite heavy use by people, rams used areas within 200 m of the trail passing through the Rae Lakes area. However, people in only 1 of 43 groups (2%) saw sheep.

Of 104 campsites investigated through­out the study area, 75% were within 50 m of water, trails, or both. ~·!any campsite areas appeared to have had heavy, re­peated use. Sheep did not currently use areas where campsites were located (El­der 1977).

912 DISTURBANCE OF BIGHOfu~ SHEEP· Hicks and Elder

Accorcling to records of peak-climbing, use has been steady and light ( <4 groups per year) for most peaks. wit. Baxter and Black Mountain have had increases. in use, up to 14 groups per year. Our obser­vations indicated that both peaks are q.lso important areas for sheep. A number of climbers in recent years have made as­cents in violation of Bighorn Zoological Area regulations, as evidenced by 2 ille­gal climbs of wit. Mar; Austin in 1974 and 1976, and 6 ascents of Black Mountain in 1975. Records failed to yield enough in­formation to determine accurateiy how many climbers had encountered sheep.

Encounters Between Humans and Sheep

Twenty incidents of human-sheep in­teractions were observed: 10 involved hikers, 9 involved study personnel, and 1 involved a pack-party of 23 people and 20 horses. Fifteen interactions (9 involv­ing hikers) occurred on Baxter Pass and 5 occurred in other areas of the summer range.

Of 58 groups of hikers observed cross­ing Baxter Pass, 9 groups crossed while sheep groups were on the pass. Similarly, 17 sheep groups were observed on the pass and 9 of these groups were there while people were on the pass. Six sheetJ groups may have left the pass because of disturbance by humans. Four sheep groups left the pass some time after the people had left, including a group that remained on the pass until darkness, pre­cluding further observation.

Distance, herd size, and elevation of humans in relation to sheep were impor­tant in determining the reaction of big­horns when approached by people. Poly­nomial regression analysis was used to describe the effect of distance (X, m) on the reaction codes of sheep (Y, 0-4) for the separate cases when humans ap-

proached from below or from above the sheep group. The equations were y (above) = 4.67 - 0.0093X + 0.000005X2 and Y (below) = 3.5 - 0.0081X ~ 0.000005X2

• Distance \vas correlated (P < 0.05) with reaction codes in both situa­tions. The results indicate that an ap­proach from above is more likely to elicit a reaction (r2 = 0.68) than an approach from below (r2 = 0.33) at an equal dis· tance. Sheep usually run uphill toward rocks when alarmed. If this avenue of es­cape was cut off by the approach of hu­mans, sheep reacted by quickly running to a position where upward flight was possible. Similar observations were re­ported by Light and \Veaver (unpub­lished, U.S. Forest Service, San Bernar­dino National Forest, California) for desert bighorn sheep (0. c. nelsoni).

Small sample size precluded testing the effect of bighorn group size on reac­tion code. However, several observations seemed to suggest that smaller groups were more susceptible to human distur­bance. In all cases (3), "solitary"' ewes (with or without lambs) left Baxter Pass as humans appeared. Conversely, a group of 5 sheep in the same area remained bedded as hikers approached to within 160 m. This may reflect security that sheep derive from being in groups.

These relationships apply to groups of ewes, lambs, and yearlings. Ram groups may have demonstrated a different pat­tern of behavior. For example, from above we approached to within 100 m of a group of 18 rams that showed only a code 1 (curious) reaction.

Bighorn Use of Meadows and Trails Human-use meadows were used less

by sheep than human non-use meadows (P < 0.05). However, this cannot be at­tributed to human activity because im· portant differences in vegetative compo-

]. Wildl. ~Innage. 43(4):19i9

sition occurred betv. · 1neadows. A N range test was used O\VS for differences eover (Zar 1974:151 meadow (a human-us 0.05) vegetative co" meadows. However meadows (incluu..•"~'" meadow, another h not different (P > 0. er.

Lower Sumn1it m discernible use by suitable forage was meadow was surro grnwth of willows sual surveillance vented wary ewes Ewe groups crossed utilized meadows b meadow near willows did not personal co

Bighorn pellet g was correlated (r2 = the percentage of present (X) in each 0.48X). The Oak F were consistently hi • clue to their proxim \Vhich enhances th horns. Bighorn us meadow pellet · correlated with tb slopes (r2 = 0.93, P

Foot-trails throug Baxter summer affect sheep n1ovem yearling groups on bedded along the paths. Ram groups ing trails to trave move into areas of to heavy human frequency of pellet

J. Wildl. ~lanage. 43l-1

DISTUHBA~CE OF BIGHOR."l" SHEEP • Hicks and Elder 913

or from above tJ1c · sition occurred between the 2 kinds of equations were y meadows. A Newman-Keuls multiple

range test \Vas used to compare the mead­. O\VS for differences in percent vegetative

+ 0. 00.0005X 2

3.5 - 0.0081X _;. was correlated (P <

codes in both situa­ndicate that an ap­Inore likely to elicit

tllan an approach 3) at an equal dis­

y run uphill toward If this avenue of es­the approach of hu-' . k1 oy qu1c . Y running upward flight \vas

servations were re­d Weaver (unpub­ervic:e~ San Bernar­st, California) for (0. c. nelsoni). precluded testing

group size on reac­observations

;mailer groups human distur-

3)~ "solitary" ewes s) left Baxter Pass

versely, a group area remained

ed to within Beet security that ng in groups. apply to groups of in.gs. Ram groups d a different pat-r exatnple, from

to within 100 m of showed only a

ows and Trails ·s \Vere used less non-use meadows his cannot he nt­vity because im­getative compo-

30 0 Current Year Groups

<tcover (Zar 1974:151-155). Baxter Lake co 25

""' r-meadow (a human-use area) had less (P < ~ 20 ~Old Groups

~0.05) vegetative cover than all the other -~meadows. HO\vever, the remaining 5 ~ 15 ~meadows (including Lower. Summit ::l

0 1-meadow, another human-use area) were (5 10 ~not different (P > 0.05) in vegetative cov­~er. ~·~ Lower Summit meadow received no ~discernible use by bighorns. Although "' ~suitable forage was abundant, the entire ~meadow was surrourtded by a dense ;. growth of \\dllows which obstructed vi­~rsual surveillance and apparently pre­~·vented wary ewes from entering the area. ~Ewe groups crossed canyon bottoms and ~~utilized meadows below Lower Summit ~~ineadow near human foot-trails where ~willows did not grO\v (John 'VVehausen, · . personal communication). · : Bighorn pellet group deposition (Y) - ·.:was correlated (r2 = 0.54, P < 0.01) with

.the percentage of preferred forage species -present (X) in each location (Y = -4.09 +

.. ·" 0.48X). The Oak Fork meadow transects ::were consistently high in pellet groups,

· .'due to their proxhT)ity to rocky slopes, .~.'·~which enhances their desirability to big­~.· horns. Bighorn use of the Oak Fork ~ meadow pellet transects \vas negatively .. correlated with the distance to rocky ~.slopes (r2 = 0.93, P = 0.01). ~ . it'~ Foot-trails through areas of the :\'It. #f· Baxter smnmer range did not adversely t'f;;; affect sheep movements. Ewe, lamb, and ~· yearling groups on Baxter Pass fed and ~?bedded along the edge of these foot ~·paths. Ram groups frequently used hik­~ ing trails to traverse forest cover and t? move into areas <:>f co:n.current moderate ~· to heavy human use. Figure 2 sho\vS the

frequency of pellet groups relative to dis~

· J. Wildl. ~Ianage. 43(4):1979

..... (!) 5 Cl,) a.

10 20 30 40 50 60 Distance from Trail (m)

Fig. 2. Ftequency of bighorn pellet groups ne3r the Bax­ter Pass trail, Sierra Nevada, 1976. Data ere from 2 tran­sects on the south side of Baxter Pass.

tance from the Baxter Pass trail. The trail cut through the largest patch of vegeta­tion on the south side of the pass. Sheep use was high at this location as they uti­lized the available forage.

DISCUSSION

Past vs. Present Human Use Recreational use of designated wild­

erness areas has increased steadily (Schoenfeld and Hendee 1978:31-36). In 1975, the John .\1uir Wilderness (in which the California Bighorn Zoological Area lies) was the most heavily used na­tional forest wilderness in the country. It received nearly 1.4 million visitor-days (Stankey et al. 1976). The mode of travel in the Sierra high country has shifted from packtrain and horseback to highly mobile backp~:tckers (Dunaway 1971b ). Although most of this use is limited to trails and designated campsites, these trends nevertheless point to increasing human activity in an area of limited sheep habitat. 1fanagement of the Sierra

•

914 DISTURBANCE OF BIGHOfu~ SHEEP •Hicks and Elder

bighorn will necessarily involve manage­ment of the visitors to the area and their recreational activities.

Poaching of bighorns and competition with domestic livestock, 2 major human­related factors in the historical decline of mountain sheep, have been eliminated by Forest Service administrative prac­tices. Current human activity in the Zoo­logical Area consists largely of hiking, fishing, ca1nping, peak-climbing, and photography.

Evaluation of Human Disturbance Our observations of the Mt. Baxter

sheep indicate that the herd is not de­clining due to recreational use of the area. Recruitment rates are high, lamb survival appears to be excellent, and few cases of diseased or infirm animals were noted. Predation is not a major factor (Jones 1950).

This study indicates that humans and bighorns in the .Mt. Baxter summer range usually are separated spatially. Interac­tions have been minimized by prefer­ence of people to camp near water and trails. Bighorns inhabit many other areas where these features do not exist. Intru­sions into bighorn areas were transitory since the purpose was to travel through the area or see some feature, such as peaks or bighorns, and then depart. Areas of frequent contact were limited to spe­cific areas, such as the Baxter Pass trail; and the bighorn sheep did not seem to be affected adversely. Bighorns contin­ued to return to Baxter Pass despite re­peated encounters with humans, and have becnme conditioned to hikers on the Baxter Pass trail. Sheep on the pass can usually watch people approach from a distance and from below minimizing the alarm reaction of sheep. Bighorns also used areas near concentrations of

recreationists in the Rae Lakes area but interactions were infrequent.

Humans are not crowding bighorns out of meadows in the .Nit. Baxter area. Few of the available summer range meadows are frequented by recreationists. In meadows used by both bighorns and hu­mans, use by sheep is positively related to vegetative cover and preferred forage species. T~us, overall distribution of big­horns was related positively to food re­sources and not negatively to human presence and use.

The results of this study were based on the current hiker use of the Bighorn Zoo· logical Area, which was below the maxi­mum Bighorn Zoological Area limit of 25 per day. Increased recreational use might adversely affect bighorns in the Mt. Bax­ter area. Light and vVeaver (unpublished, U.S. Forest Service, San Bernardino Na­tional Forest, California) found that in­tense recreational activity reduced desert bighorn occupancy of an area in the San Gabriel i\1ountains of southern Califor­nia. The i\1t. Baxter herd has been iso­lated from heavy human use by the nig­ged character of the area, and access only by backpacking or use of pack stock. Our management recommendation is to con­tinue current regulations with increased restrictions on off-trail hiking and altera­tion of the Baxter Pass trail to route peo­ple away from areas intensely used by sheep.

LITERATURE CITED ALnL-\NN, J. 1973. Observational study ofbehav­

ior: sampling methods. Behaviour 49:227-.265. DUNAWAY,. D. J. 1971a. Bighorn sheep habitat

management on the Inyo National Forest, a new approach. Des~rt Bighorn Counc. Trans. 15:18-!23.

--. 19'7lb. Human disturbance as a limiting factor of Sierra Nevada bighorn sheep. Trans. First :;-.;·orth Am. Wild Sheep Con£ 1:165-173.

ELDER, J. M. 1977. Human interactions with Sierra

J, vVildl. ~1anage. 43( 4):1979

Nevada bighorn sheep: · M.S. Thesis. Univ. of ~1 PP•

GEIST, V. 1971. ~1ountain havior and evolution. U · Chicago. 383pp.

--. 1975. On the man sheep: theoretical 105 in ]. B. Trefethen, modern North America. York.

HANSEN, C. G. 1971. reducing desert Bighorn Counc. Trans.

HICKS, L. L. 1977. Human Baxter herd of Sierra M.S. Thesis. Univ: of i\ 57pp.

JO~ES, F. L. 1950. A survey · bighorns. Sierra Club . jORGENSEN, P. D., AJ.~D D. B.

ifornia bighorn sheep herd unit. Calif. Dep. (Mimeo.)

J. \Yildl. ~Ianage. 43(4):

Rae Lnkes area but quent.

'ng bighorns out It. Baxter area. Fe\\

er range meadows recreationists. In

bighorns and hu­positively related

preferred forag(• distribution ofbig­

vely to food re­vely to human

y were based on the Bighorn Zoo­below the maxi-

al studv of bdw · ur ·19:227 -~w; sheep hahit,t!

National Fon.•:.l. •' Counc. Tr,111,

bance as a limitith! ghom sheep. Trall' · Con£: 1:165-17 ~ ractions with Skn.•

. 43(4): w7~l

DISTURBANCE OF BIGHOfu'l SHEEP • Hicks am[ Elder 915

Nevada bighorn sheep: the ~1t. Baxter herd. ~LS. Thesis. Univ. of .Michigan, Ann Arbor. 93

• pp. t GEIST, V. 1971. .Mountain sheep: a study in be­

havior and evolution. Univ. of Chicago Press, Chicago. 383pp.

1975. On the management of mountair~ sheep: theoretical considerations. Pages 77-105 in ]. B. Trefethen, ed. The wild sheep in modern North America. \Vinchester Presr., New York.

C. G. 1971. Overpopulation .u a factor in reducing desert bighorn populations. Desert Bighorn Counc. Trans. 15:46-52.

E"-...... ~ . .-v, L. L. 1977. Human disturbance of the Mt. Baxter herd of Sierra Nevada bighorn sheep. M.S. Thesis. Univ. of ~fichigan, Ann Arbor. 57pp.

ONES, F. L. 1950. A sun·ey of the Sierra Nevada bighorns. Sierra Club Bull. 35(6):29-76.

, P. D., AND D. B. SCHAUB. 1972. Cal­ifornia bighorn sheep survey-:\1t. Langley herd unit. Calif. Dep. Fish Game Rep. 7pp. (Mimeo.)

· 'Vildl. ~fanagc. 43(4):1979

:\fCCULLOUGH, D. R., AND E. R. SCHNEEGAS. 1966. \Vinter observations on Sierra Nevada bighorn sheep. Calif. Fish Game 52:68-84.

SCHOENFELD, C. A., AND ]. C. HENDEE. 1978. Wildlife management in wilderness. Boxwood Press. Pacific Grove~ Calif. 172pp.

. STANKEY, G. H., R. C. LUCAS, AND D. W. LIME. 1976. Crowding in parks and wilderness. De­sign and Environ. 7(3):38-41.

U.S. DEP. INTERIOR. 1966. Rare and endangered fish and wildlife of the United States. Resour. Pu bl. 34. 166pp.

WEAVER, R. A. 1972. California bighorn in the Sierra Nevada mountain range. Calif. Dep. Fish Game, Wildl. Manage. Admin. Rep. 72-7.17pp.

WOODWARD, T. N., R. J. GUTIERREZ, AND W. H. RUTHERFORD. 1974. Bighorn lamb produc­tion, survival and mortality in south-central Colorado. J. Wildl. Manage. 38:771-774.

ZAR, J. H. 1974. Biostatistical analysis. Prentice­Hall, Englewood Cliffs, N.J. 620pp.

Received 31 March 1978. Accepted 5 Apri/1979.