*rs o_ r s ..

Population Estimation and Monitoring L

BIGHORNSHEEP DISTRIBUTIONAND ABUNDANGE 539 3_ . .z.A.

..... <_ _ iP_ IFE _ i:_ e; z. , .-tE _X- ;.>v.<,Peninsular Ranges, California.

Distribution and abundance of bighorn sheep in the Peninsular Rangess, California

Esther S. Rubinn,alter M. Boyces,Mark C. Jorgensens,Steve G. Torress, CharlesL. Hayess,Chantal S. O9BrienX,and David A. Jessup

Abstract We examinedthe currentpopulation structure and past trends in abundanceof endangeredbighorn sheep(Ovis canadensis) in the PeninsularRanges of Californiausing a varietyof approaches.Direct observationsof radiocollaredanimals (N= 90 ewes and 24 rams)during 35 monthssuggested that bighorndistribution in the PeninsularRanges was fragmented into 28 groupsof ewes. Thesefindings were supportedby aerial-telemetrylocations of radiocollaredewes obtainedduring 43 fixed-wing flightsand observations of uncollaredbighorn sheep madeduring 2 helicoptersurveys. Boundaries betweenewe groupscoincided, in 4 cases,with paved roads, leading us to speculatethat some frag- mentationwas recentand artificial. Abundance estimates derived for 5 of the 8 ewe groupsin 1994 and 1996 revealeda recentdecline of 28% in thisportion of the range.Adult population estimates weregenerated and combined with existing estimates for the remainderof the rangeto producees- timatesof 347 and 276 bighornsheep in the PeninsularRanges north of the UnitedStates-Mexico borderin 1994 and 1996, respectively.Linear regression analysis of 26 yearsof waterholecount data,collected at 30 sitesrepresenting regions used by 4 ewe groups,indicated that numbers of ewes haddeclined in 2 of these regionssince 1971, butthat 2 regionshad been inhabitedby stableewe populationsduring this period. We suggestthat groups of bighornsheep in differentportions of the PeninsularRanges are under local influences and exhibit independent population dynamics. Keywords bighorn sheep, California,distribution, Ovis canadensis, PeninsularRanges, population fragmentation,population trends

Address for EstherS. Rubin: Department of Veterinary Pathology, Microbiology, and Immunology, University of California, One Shields Avenue, Davis, CA 95616, USA, and California Department of Fish and Game, 1416 Ninth Street, Sacramento, CA 95814, USA. Address for Walter M. Boyce (correspondingauthor), Charles L. Hayes, and Chantal S. O'Brien: Department of VeterinaryPathology, Microbiology, and Immunology, University of California,One Shields Avenue, Davis, CA 95616, USA. Present address for Charles L. Hayes: New Mex- ico Department of Game and Fish, P.O. Box 251 12, Santa Fe, NM, 87504, USA. Present address for Chantal S. O'Brien: P.O. Box 540, Borrego Springs, CA 92004, USA. Address for MarkC. Jorgensen: Colorado Desert District, CaliforniaState Parks,200 Palm Canyon Drive, Borrego Springs, CA 92004, USA. Address for Steve G. Torres: California Department of Fish and Game, 1416 Ninth Street, Sacramento, CA 95814, USA. Address for David A. Jessup: California Department of Fish and Game, 1451 ShafferRoad, Santa Cruz, CA 95060, USA.

Wild}fe Society Bulletin 1898, 26(3):538-551 Peer refereed 540 WildlifeSociety Bulletin 1998, 26(3):53>551

Bighorn sheep (Ovis canadensis) in the Peninsular Ranges (the Santa Rosa Mountains [DeForge et al. Ranges of California are thought to be distributed 1995]), but current abundance estimates do not exist among 7 mountain ranges (Weaver 1972; Fed. Regis- for the remainder of the range. In the Santa Rosa ter, Vol. 57, No. 90, 1992) and to comprise a Mountains, early (1957-1976) estimation techniques metapopulation (Torres et al. 1994, Bleich et al. 1996, differed from those used more recently, making iden- Boyce et al. 1997). Bighorn sheep in these ranges tification of long-term trends in abundance difficult. have been listed as threatened by the state of Califor- Waterhole count data were used for early estimates, nia since 1971 (Calif. Dep. Fish and Game 1992), and whereas annual helicopter surveys were used to gen- have recently been listed as endangered by the U.S. erate estimates starting in 1977. Helicopter surveys Fish and Wildlife Service (Fed. Register, Vol. 63, No. have indicated a population decline during 52, 1998). A primaryreason for the federal listing was 1977-1982 (Wehausen et al. 1987) and 1982-1995 a reported decline in numbers of bighorn sheep dur- (DeForge et al. 1995) and suggest a large decline in ing the past 25 years. Population estimates were as numbers relative to earlier estimates (DeForge 1984, high as 971 in 1972 (Weaver 1972) and 1,171 in 1974 DeForge et al. 1995). It is not known, however, if this (Weaver 1975); more recent estimates were 570 in decline was rangewide or if helicopter survey esti- 1988 (Weaver 1989), 400 in 1992 (Fed. Register, Vol. mates can be compared to early (pre-1977) estimates. 57, No. 90, 1992), and 327-524 in 1994 (Torres et al. We used locations and movement patterns of radio- 1994). Disease, drought, habitat destruction and collared bighorn sheep, as well as observations of un- modification, and resource competition have been hy- collared bighorn sheep, to describe the spatial pattern pothesized to have contributed to this decline (De- of distribution of ewes in the Peninsular Ranges. We Forge and Scott 1982, DeForge et al. 1982, Turner and generated current abundance estimates for bighorn Payson 1982, Cunningham and Ohmart 1986, We- sheep south of the Santa Rosa Mountains from aerial hausen et al. 1987, Sanchez 1988, Mullens and Dada helicopter survey data. In addition, we analyzed a 26 1992). Research addressing these factors has in- year data set of annual waterhole counts of bighorn creased our knowledge about Peninsular bighorn sheep that were conducted in selected portions of the sheep; however, their spatial distribution has not range outside of the Santa Rosa Mountains to assess been determined, a current population estimate does long-term population trends. Our objectives were to not exist for the entire range, and past abundance (1) describe the distribution of bighorn ewes in the trends in most of the range are poorly understood. PeninsularRanges, (2) generate current abundance es- Effective management of a species or population re- timates for bighorn sheep south of the Santa Rosa quires accurate knowledge of its spatial distribution Mountains,and (3) assess recent and long-term trends (Natl. Res. Counc. 1995). For example, potential frag- in bighorn sheep numbers in the PeninsularRanges in mentation must be identified and population dynamics regions outside of the SantaRosa Mountains. in different regions must be understood before risks to population viability can be evaluated and appropriate management strategies identified (Hanski and Gilpin Study area 1991). Fragmentation occurs as a result of natural The PeninsularRanges are located in southern Cali- processes (e.g., habitat heterogeneit,v,behavioral char- fornia and Mexico, in the Colorado Desert division of acteristics [Gilpin 1987, Bleich et al. 1990]) or artificial the Sonoran Desert (Ryan 1968; Fig.l). On the north, processes (e.g., habitat loss due to increased human the PeninsularRanges are bordered by the Transverse land use, barrierssuch as fences or roads [Wilcove et Ranges. From this point, they extend south approxi- al. 1986]). Although bighorn sheep in the Peninsular mately 225 km in Californiaand another 1,200 km into Ranges have been found to concentrate near water BajaCalifornia, Mexico. In the United States,the range sources during summer months aones et al. 1957), is from 80 to 225 km wide and the maximum elevation their spatial distribution in these ranges has not been is 3,293 m at SanJacinto Peak. Bighorn sheep inhabit examined. Identifyingdiscontinuities in distributionis the east-facingside of the PeninsularRanges in habitat the first step towards understandingthe causes of frag- characterized by steep slopes and cliffs, canyons, and mentation and the resulting spatial structure of big- washes. On the eastern side, vegetation associations horn sheep populations in this geographic area. are coniferous forest, primarilyponderosa pine (Pinus If distribution is discontinuous, then abundance es- ponderosa) and white fir (Abies concolor), 21,800 m; timates and knowledge about the dynamics of each chaparral, 21,500 m; and pinyon pine (P. mono- spatial subunit will be required to assess population phylla)-juniper (Juniperus californica), 21,200 m. viability (Gilpin 1987, Boyce 1992). Recent survey ef- Lower elevations are dominated by agave (Agave de- forts have concentrated on 1 portion of the Peninsular serti)-ocotillo (Fouquieria splendens), cholla (Opun- Bighornsheep distributionand abundance @ Rubinet a1. 541

capture, at approximately 30-day intervals. On 2 oc- casions animals were observed from a helicopter, but most (298%) observations were made from the ground. Data collected at the time of each sighting in- cluded date, time, geographic location {IJniv. Trans- verse Mercator coordinates), group size, group com- position, and the presence of other collared animals. Collared bighorn sheep were located through Sep- tember 1995. From February 1994 through Septem- ber l99S, bighorn sheep also were monitored in this same manner in the Santa Rosa Mountains west of Highway 74, where we identified all ewes and most rams by the presence of radiocollars and eartags. Bighornsheep habitat,Peninsular Ranges, California. Bighorn ewes typically exhibit a greater degree of philopatric behavior than rams (Geist 1971). There- tia spp.)-palo verde (Cercidium forgdum), and cre- fore, we determined spatial population structure from osote (Larrea tridentata)- palo verde-mesquite locations and movement patterns of females. We used (Prosopis spp.) associations (Ryan 1968). Bighorn the program CAIMOME(Kie et al. 1994) to generate a sheep most frequently have been found at elevations 100%minimum-convex-home-range polygon ICP) for <1,400 m Forgensen and Turner 1975), typically stay- each radiocollaredewe. Eachpolygon was based on all ing below the pinyon pine-juniper vegetation associa- observations made of a particularewe during the study tion. Maximum temperature in bighorn sheep habitat and was used to spatiallydetermine the outline, rather often reaches 46°C in the summer months, and winters than area, of her home range. We assumed that ewes are mild, with temperatures occasionally reaching with overlapping or partiallyoverlapping home ranges freezing. Annual rainfall is variable with maxima of were members of the same home-range group (Geist 35-470 mm during the past 36 years. Rainfallexhibits 1971) and that discontinuities betsveen these groups a bimodal distributionpattern with most (approx 70°/0) represented a fragmentation in the distribution of occurring in the winter months and a lesser amount in the late summer months (Natl. Oceanic and Atmo- spheric Adm., 1962-1997). We discuss the portion of the PeninsularRanges located within the United States.

Methodls Between fall 1992 and fall 1993, we captured and radiocollared 98 bighorn sheep (82 ewes and 16 rams) east of Highway 74 in the SantaRosa Mountains and north of Interstate 8 (Fig. 1). Radiocollared big- horn sheep were already present in the Peninsular Ranges west of Highway 74 as part of ongoing proj- ects conducted by the California Department of Fish and Game and the Bighorn Institute. Our goal was to place radiocollars on sheep throughout the remainder of the range. Previous ground- and aerial-reconnais- sance surveys had identified areas occupied by big- horn sheep, and we attempted to collar animals in each of these areas. We captured bighorn sheep via netgun from a helicopter; each animal was aged and fitted with an identifiable eartag and a radiocollarwith a unique frequency (Telonics Inc., Mesa, Ariz.). We Fig.1. PeninsularRanges in southernCalifornia. Each * indicatesa processed and released bighorn sheep at capture lo- waterholecount site in Anza-BorregoDesert State Park. Sitesare cations or at a base camp <5 km from the capture site. showngrouped (circled) to correspondto 4 of the ewe groupsiden- tifiedin this study(from north to south):Coyote Canyon, north San We attempted to locate and observe every radiocol- YsidroMountains, south San Ysidro Mountains, and Carrizo Canyon. lared animal at least once per month, from the time of Thickgray line depictsAnza-Borrego Desert State Park boundary. 542 WildlifeSociety Bulletin1998, 26(3):53>551 ewes. In some portions of the range, we found clusters ings concurred with home-range polygons derived of ewes that were connected to each other by the from ground observations of collared ewes. home range of only 1 ewe. In each of these cases we Data collected during the helicopter surveys were examined the movement of the ewe with respect to used to generate population estimates south of the number, duration, and frequency of movements be- Santa Rosa Mountains. For this analysis, bighorn tween groups to determine whether or not these move- sheep were classified as ewes and rams (lambs were ments represented infrequent intergroup moves. excluded), and estimates were generated for the ewe In addition to our direct observations, the general lo- population and total population (rams and ewes com- cations of radiocollaredbighorn sheep were monitored bined). The number of radiocollared animals present during fixed-wing aircraftflights conducted south of in each sampling polygon was determined just prior the SantaRosa Mountains. Flightswere conducted 1-2 to or during each flight, using aerial, fixed-wing or times per month in a Cessna 185 aircraft. Radiocollared ground monitoring. Collared bighorn sheep were bighorn sheep were located using a telemetry receiver used as marked animals, and population estimates that was installed in the aircraft,and the general loca- were generated using Chapman's(1951) modiElcation tion of each animalwas recorded by a biologist familiar of the Petersen estimator (Seber 1982). The popula- with the topography of the study area. We placed 5 ra- tion estimate (N) was defined as: N = [(nl + l)(n2 + diocollars in locations unknown to the flight crew to l)/(m2 + 1)] - 1, where n, is the number of collared verify the accuracy of this technique and determined animals in the sampling area, n2is the total number of that a maximum error of approximately 1 km existed. animals observed, and m2is the number of collared an- We considered this level of accuracy sufficient because imals observed. Estimateswere generated for the en- we used these data simply to verify the home ranges tire survey area and also for individual ewe groups generated from ground observation. within this area, using the number of collared bighorn We conducted helicopter surveys between the (nl and m7) in the entire survey area or in specific ewe Santa Rosa Mountains and the United States-Mexico group areas. Confidence intervals (95%) were calcu- border in October 1994 and October 1996 to obtain lated as N + 1.96 (variance of N)05, with the variance data on bighorn sheep distribution and abundance. (var) defined as var = [(n,+ l)(n2+ l)(nl - m2)(n2 - Each survey was conducted during a 4- to 5-dayperiod. m2)]/[(m2 + 1)2(m2+ 2)] (Seber 1982:60). Using the Sampling polygons representing potential bighorn method described by Seber (1982:121), we examined sheep habitat (approx 150- to 1,300-m elevation) were the change in population estimates for 1994 and 1996 delineated prior to the flights. In 1996, 3 sampling by testing the null hypothesis of Ho N1994= N1996, polygons were excluded from the survey. We ex- where Z = [(N1994- Nl996)]/[(varl994 + varl996) ]. cluded the Fish Creek Mountainsand the areabetsveen Annual waterhole counts of bighorn sheep were Interstate 8 and the United States-Mexico border be- conducted at 49 sites during 1971-1996 in selected cause we had observed only 1 ram and no bighorn portions of the Peninsular Ranges (Fig. 1). These sheep in these regions, respectively, during the 1994 counts were conducted in mid-summer (end of survey (Fig. 1). In addition, we excluded the Coyote Jun-early Aug), which is a hot and dry time of year Mountainsbecause we did not observe bighorn sheep (since 1962, x high temp = 41.7° C and x total rainfall during the 1994 survey and our ground observations = 8.1 mm for Jul) and, thus, an ideal time in which to indicated that bighorn used these mountains primarily conduct a waterhole count. The counts were orga- in winter and spring. During these surveys, we flew nized by Anza-Borrego Desert State Park staff and over bighorn sheep habitat at 40-60 kour, follow- carried out by volunteers at sites representing natural ing topographical contours at 100- to 150-m intervals. springs and 2 man-made drinkers. Counts typically IEree observers accompanied the pilot in a Bell 206B- were conducted during daylight hours for 3 consecu- IIIJetRanger helicopter. The pilot and observers were tive days, during which all observed bighorn sheep not aware of the locations of radiocollaredanimals and were recorded and classified (age and gender). telemetry was not used to locate groups or individuals. Nineteen sites which were only counted during a As each polygon was systematically surveyed, the lo- few years were eliminated from the analysis. We cation and classification of each bighorn sheep ob- grouped the remaining30 count sites into 4 geographic served were recorded. Bighornwere classified as year- regions that represented 4 separate ewe groups (as ling ewe, adult ewe, yearling ram, Class II ram, ClassIII identified in this study) and carried out separate data ram, Class IV ram, or lamb (classiElcationsmodified analyses for each area and combination of areas. Our slightly from those used by Geist 1971). We examined analyseswere restrictedto yearlingand adult ewes, and locations of ewes (collared and uncollared) observed count data from each year were converted to number during these surveys to determine whether these sight- of ewes observed per day. We added a constant of 0.5 Bighornsheep distributionand abundance * Rubinet al. 543

to each count because counts of zero existed. We then vealed that the distributionof ewes was not continuous examined the natural log of the number of ewes in the PeninsularRanges. Observed discontinuities in counted (per day) each year with linear regression overlapping 100% MCP home ranges (fragmentation) analysis using the program StatMost(DataMost Corp., resulted in the following provisional assignments of Sandy,Ut.). Eberhardtand Simmons (1992) advocated ewe groups south of the SanJacintoMountains: (1) Car- the use of linear regression on the log scale for studying rizo Canyon, (2) south Vallecito Mountains, (3) north long-term population trends, and Hatfieldet al. (1996) Vallecito and SanYsidro Mountains,(4) Coyote Canyon found that simple linear regression provided a power- and SantaRosa Mountainseast of Highway 74, and (5) ful test for detecting long-term trends in raptorcounts. SantaRosa Mountainswest of Highway 74. We tested the null hypothesis that there was no change The connection between ewes in the San Ysidro in the number of ewes counted per day across years Mountains and ewes in the north Vallecito Mountains (slope of the regression line = 0) and determined the was dependent on the home range of a single ewe, No. significance of the regression analysisusing a 2-tailedt- T7. Ewe No. T7 was captured in the south San Ysidro test (Sokal and Rohlf 1995) and a randomization test Mountains,and her movements out of this area (across (Collins 1990, Manly 1991), using the program RT county road S-22 into the north San Ysidro Mountains (Manly 1996). We examined the potential effects of and across Highway 78 into the Vallecito Mountains) temperatureand precipitation as covariatesinfluencing were infrequent (n = 1 and 2, respectively) and brief the number of ewes counted each year, using a Spear- (perhaps <1 day in each case). This ewe had the man rank correlation analysis (Sokal and Rohlf 1995). largest home range of ewes in the San Ysidro Moun- The highest temperatureduring the 3 days of the count tains, although she was located fewer times (n = 28) was used to examine the effect of temperature. We ex- than other ewes in these mountains (x = 49.8, n = 19 amined the relationshipbetween precipitation and the ewes). We concluded that her movement patterns number of ewes counted using 2 subsets of precipita- across these roads were atypical of other ewes and tion data: (1) the cumulative rainfallfor the 3 months likely represented exploratory movements. When preceding the count, and (2) the cumulative precipita- data for this ewe were removed from the analysis, the tion during November-Februaryin the winter preced- remaining ewes formed 3 separate groups: 1 group in ing the year of the count. These 2 subsets were se- the northern Vallecito Mountains, 1 in the south San lected because rainfall directly preceding the count Ysidro Mountains,and 1 in the north SanYsidro Moun- may create temporary additional water sources that tains, with road S-22 separating the 2 latter groups. could influence visitation of sheep to the counted sites, Similarly,the home range of a single ewe, No. X3, was and winter precipitation may have a positive influence the only observed link between ewes in Coyote on recruitment rate (Douglas and Leslie 1986, We- Canyon and those in the Santa Rosa Mountains. Ewe hausen et al. 1987), thereby increasing the number of No. X3 was first captured near Deep Canyon, just east (yearling) ewes counted 1.5 years later. Precipitation of Highway 74 in the SantaRosa Mountains,in the fall and temperature data were collected in Borrego of 1993. This ewe was observed outside of this area Springs, located within 5-55 km of each waterhole (in Coyote Canyon and south of Martinez Canyon in count site. Clirnatedata collected at this site were as- the Santa Rosa Mountains) in 3 consecutive sightings sumed to be representativeof climate patterns at all wa- during a 3-month period in 1994, representing 6% of terhole count sites, because precipitation and tempera- our observations of this ewe. She was then observed ture were each found to be significantly correlated consistently near Deep Canyon for the next 28 months (product moment correlation r 2 0.94, P < 0.000, and r until she died of unknown causes. Therefore, we re- 2 0.89, P < 0.000 for monthly high temperatureand to- garded this as a possible exploratory movement be- tal precipitation, respectively) among 3 climate data tween ewe groups. When data for ewe No. X3 were collection sites (Deep Canyon, Borrego Springs, and removed from the analysis, this group (Coyote and Ocotillo) located 50-100 km apart in the Peninsular Santa Rosa Mountains, east of Highway 74) separated Ranges (Natl. Oceanic and Atmospheric Adm. into 4 groups; 3 groups in the Santa Rosa Mountains 1962-1997). east of Highway 74 (in and around Deep Canyon, Mar- tinez Canyon, and the south Santa Rosa Mountains) and 1 group in Coyote Canyon. Results Based on these observations, we identifiledsepara- Distribution tions among the following groups of ewes south of We made 3,149 direct observations of 90 radiocol- the SanJacinto Mountains:Carrizo Canyon, south Val- lared bighorn ewes (Table 1). Examinationof the over- lecito Mountains, north Vallecito Mountains, south lap of 100%MCP home ranges of radiocollaredewes re- San Ysidro Mountains, north San Ysidro Mountains, 544 WiidlifeSociety Bulietin1998, 26(33:53>551

Table1. Distributionof radiocollaredbighorn ewes and monitoringintensity in the PeninsularRanges, California, October l 992-September1995.

No. of Observationsper ewe Ewemonthsb Home-range radiocollared Home-rangegroupsofewes overlapa ewes x SD x SD

CarrizoCanyon a 19 39.0 11.9 28.4 7.2 VallecitoMts.C South b 2 7.0 4.2 22.0 0.0 North c 5 13.2 2.4 19.0 5.2 SouthSan Ysidro Mts. c 5 50.4 14.0 30.2 7.5 NorthSanYsidroMts. c 14 49.7 19.4 28.4 8.8 CoyoteCanyon d 8 15.0 6.4 17.3 6.3 SantaRosa Mts.-east of Hwy 74c southS.R. Mts. d 3 14.3 1.2 23.3 1.2 MartinezCanyon d 6 3.8 0.8 21.8 0.5 Deep Canyon d 13 39.2 16.5 18.9 5.4 SantaRosaMts.-westofHwy74 e 15 45.6 17.9 18.5 3.6

a Sharedletters indicate that 100% minimum convex polygonhome rangesoverlapped. b Numberof monthseach ewe was includedin the study. c Mayrepresent >1 ewe group.

Coyote Canyon, Santa Rosa Mountains east of High- of radiocollared ewes were recorded (x = 22.5 loca- way 74-south Santa Rosa Mountains, Santa Rosa tions/ewe, SD = 14.1, range = 1-40). During these Mountains east of Highway 74-Martinez Canyon, flights, nearly all radiocollaredewes were found to be Santa Rosa Mountains east of Highway 74-Deep within their individual 100%MCP home ranges gener- Canyon, and Santa Rosa Mountains west of Highway ated from our ground observations. An exception was 74 (Table 1; Fig. 2). Our observations of 2 Santa Rosa 1 telemetry location of ewe No. D2, a north SanYsidro groups east of Highway 74 (Martinez Canyon and Mountain ewe, just south of road S-22. Aerial location south Santa Rosa Mountains) and the 2 groups in the data were consistent with our speculation that the Val- Vallecito Mountains were based on a small number of lecito Mountainsmay support 2 groups of ewes; again, ewes and did not represent all months of the year. De- however, these observations were based on a small lineating separate ewe groups in these regions would number (n = 2) of radiocollaredewes in 1 group. be speculative, so we treated ewes in the Santa Rosa Direct observations and aerial-telemetry locations Mountains east of Highway 74 as 1 ewe group and all revealed 18 occurrences of ram movement between ewes in the Vallecitos as 1 group. We did not observe ewe groups. These movements were made by 5 ra- marked ewes leaving or unknown ewes entering the diocollared rams (among 5 pairs of ewe groups): 1 Santa Rosa Mountains area west of Highway 74; this ram, radiocollared in the San Jacinto Mountains (De- suggested that movement of ewes between the Santa Forge et al. 1997), moved in and out of the SantaRosa Rosa Mountains and the SanJacinto Mountainswas in- Mountains west of Highway 74; a second ram moved frequent. An additional group of ewes, reported to in- between the 2 Santa Rosa Mountains ewe groups habit the SanJacinto Mountains (DeForge et al. 1997), (east and west of Highway 74), during the rut in 1994 was therefore considered a distinct ewe group. and 1995; 2 rams each crossed road S-22 between the The locations of ewes observed during the 2 heli- north and south San Ysidro Mountains ewe groups 24 copter surveys concurred with our delineation of ewe times; and 1 ram was observed in 3 ewe groups (Car- groups south of the Santa Rosa Mountains. During rizo Canyon, south San Ysidro Mountains, and the these flights, 39% (1994) and 74% (1996) of radiocol- Santa Rosa Mountains east of Highway 74) during our lared ewes were observed, and all ewe sightings (in- study. Althc)ugh intergroup movements of some cluding uncollared animals) fell within home-range rams occurred during the rut (late summer-fall), polygons of radiocollared ewes. Lack of sightings in other movements occurred outside this period. portions of the survey area was consistent with sepa- rations between: (1) the CarrizoCanyon and Vallecito Abundance and recent population Mountainewe groups, and (2) the Coyote Canyon and trends north San Ysidro Mountains ewe groups. Between Duringthe 2 helicopter surveysin 1994 and 1996, we March 1993 and December 1996, 43 fixed-wing observed 110 bighorn sheep (in 37 groups) and 142 big- telemetry flights were conducted and 1,240 locations horn sheep (in 38 groups), respectively. These observa- Bighornsheepdistributionandabundance * Rubinetal. 545 tions resultedin a catch-per-uniteffort of 4.5 and 6.5 big- study: Carrizo Canyon, south San Ysidro Mountains, horn sheep per hour, respectively. We estimated the north San Ysidro Mountains, and Coyote Canyon (Fig. ewe population sizes for this portion of the range (Coy- 1; Table 3; Appendix A). North San Ysidro Mountains ote Canyon south through Camzo Canyon) as 141.3 (+ and Coyote Canyon were each further subdivided into 42.4) and 101.7 (+ 20.2) in 1994 and 1996, respectively, distinct canyons or sets of canyons. The number of and the total population size (excluding lambs) as 214.2 sites counted within a geographic area was not consis- (+ 64.4) and 163.0 (+ 31.2). We also generated abun- tent throughout years, but Spearmanrank correlation dance estimatesfor areasused by individualewe groups analysis indicated no significant relationship (-0.29 < Clable 2). Estimatesfor 1994 and 1996 were not statisti- rS< 0.17, P 2 0.17 for each area) between the number cally different when individual ewe group estimates of sites and number of ewes counted. The number of were considered (P2 0.11 in all cases) orwhen estimates ewes counted in Coyote Canyon declined significantly for the entire adult population were compared (P = (t-test: P = 0.03, randomizationtest: P = 0.02) at a rate 0.16). However, the 1994-1996 change in the ewe poR of 2.6%per year during 1971-1996. When the 3 sub- ulation for our entire survey area was significant (P = units within Coyote Canyon were examined individu- 0.09) if a significancevalue of P = 0.10 was chosen. ally, however, only sites in Cougar Canyon and Sheep Canyon exhibited a significant decline (P < 0.001), at a Long-term abundance trends rate of 13.1%peryear. Sites in the north and south San We grouped waterhole count sites (n = 30) to rep- Ysidro Mountains exhibited nonsignificant (P = 0.55 resent 4 of the 8 ewe groups that we identified in this and 0.46, respectively) changes in the number of ewes counted during 1971-1996. The shorter (10-yr) data set for the CarrizoCanyon area showed a significant(P = 0.03) decline of 9.9%per year in the number of ewes counted per year from 1973 to 1982. A significant correlation (rs = 0.61, P = 0.002) ex- isted between the number of ewes counted and the high temperature recorded during the count for the south San Ysidro region only. We found no signifi- cant (P 2 0.23) association between the number of ewes counted and winter precipitation during the preceding year, or between the number of ewes counted and rainfall in the 3 months preceding the count, for any region or subunit.

Discussion Distrgbution We concluded that bighorn ewes in the Peninsular Ranges exhibited a fragmenteddistribution and that 28 ewe groups existed as a result of this fragmentation (Table 1; Fig. 2). We believe that radiocollaredewes were representative of the entire ewe population, be- cause 223-30% of the ewes south of the Santa Rosa Mountainswere radiocollared(based on 1994 and 1996 ewe population estimates for this region), and all obser- vations of uncollared ewes were within areas used by Fig.2. Distributionof bighornewe groupsin the PeninsularRanges, collaredewes duringhelicopter surveysof potential big- California1992-1995. Stippledand shadedareas indicate regions horn sheep habitat. Our observationsindicated that the usedby home-rangegroups of ewes identifiedin thisstudy: 1 Xarrizo Canyon,2a-south Vallecito Mountains, 2b-north Vallecito Moun- CarrizoCanyon ewe group occurred north of Interstate tains,3-south San Ysidro Mountains, 4-north San Ysidro Mountains, 8 in the In-Ko-Pah,Jacumba, Tierra Blanca, and Coyote 5-Coyote Canyon,6a-Santa Rosa Mountains east of Highway74 (south),6b-Santa Rosa Mountainseast of Highway74 (Martinez Mountains. We did not document any movement by Canyon),6c-Santa Rosa Mountainseast of Highway 74 (Deep ewes between these mountainsand the VallecitoMoun- Canyon),7-Santa Rosa Mountains west of Highway74, 8-SanJacinto tains,which were occupied by the next closest group of Mountains(- indicatesgeneral location of thisgroup, DeForge et al 1997). Widehatch marks indicate possible connectivity between ewe ewes. The Vallecito Mountainsmay be inhabited by >1 groupsin theVallecito Mountains and the SantaRosa Mountains. ewe group, but this needs to be confirmedby additional - C o m- o tN -_ en O - avO o* =o- lcL£: - cYn 2 - o- QzX m o

546 WildlifeSocietyBulle*7 1998, 26(3):53W551

observations. Ewes in the San Ysidro Moun- 0u] 3s jO{s5hn O O O O O O O - tains appeared to be distinct from groups in

Q._ .t both the Vallecito Mountains and Coyote Canyon and formed 2 ewe groups, 1 on each side of road S-22. The movements of ewes No. T7 and No. D2 revealed that ewe groups in the o 4 - C C San Ysidro Mountainsand the Vallecito Moun- .E o o gS > a.v > av s;n tains were linked by infrequent, exploratory ._ . n Ct ._ . _ , v) movements of ewes. However, ewe move- o 9 ,, 9 o < o O G C ment between these groups was clearly lim- : ._ - o o Os o 55 o r X =5 X ) czb . - ited, and we did not document any permanent *i n . -

O X C C C r O < - emigration. Coyote Canyonapparently was in- *: e (x5 : O C U m Q > L Q cr) habited by a distinct group of ewes. Excluding 1 temporarymovement by ewe No. X3, we did not observe bighorn sheep moving betsveen Coyote Canyon and the SantaRosa Mountains. / - E / - E - - cD o N oo ,4 oo ( In the SantaRosa Mountains,our data revealed cO N cO - o Lm t i o a division between ewes on the west side of o £ w0 I < I U X

- I n oo r m oo m Ln o Highway 74 and those on the east side. Big- oo N un N u: x z - - - o N o horn sheep in the SantaRosa Mountainseast of Lew . . o n < c - v Cs hn Lr - Q this highway may comprise >1 ewe group, but O tr o additional observations would be needed to 5

.l - delineate other ewe groups in this area. Move-

. u . o - Q ment of ewes between the SantaRosa Moun- . - - u) - Ln Lr < £ oo - < - . . tains and the San Jacinto Mountains was not o co __ Ln z co a-> e . l t ? O observed in our study or that of DeForge et al. a) . . Lr U t oo m LO U (1997). _ _ . . - o o Although population structure can be de- . . ,,, m - O av C. oo CD a . - t = u) U Q scribed at several hierarchical scales (Hanski m Lr < Q . c55 v - and Gilpin 1991), hn . s w_ we selected groups of ewes

ur

. - with overlappinghome ranges as a meaningful

av o cL av - t unit with which to examine the distributionof 9 9 X F m X bighorn sheep in the Peninsular Ranges. I a o a) C 2 l o I D C - Q . - - Young ewes typicallylearn their home ranges Q Ln Ur, U Lr o m by following their mothers and other older fe- . . . C _ v Lrz n o . U C , - m o C males and show a high degree of philopatryto c o o their home ranges throughouttheir lives (Geist ._ .Y . .S t ca o 9 1971). Consequently, ewes with overlapping - - Q o .tO Q 0 o W° (r, CD (or partiallyoverlapping) home ranges may be . . oo Q Lr o O w < more closely relatedto each other than to other l l 3 Lm . oF o . . Lr . _ ewes Oiesta-Bianchet1991). The natalphilopa- X _ a o o oo . . . try exhibited by ewes also reduces the likeli- N Ln c G) Q : hood that ewes will colonize new areas. We

E 2' e therefore assumed that groups of ewes with m ' F overlappinghome ranges form units that have rs N X a; 0 O U O ecological and evolutionary sigsificance with (,, U) - a; Q I I respect to the genetic and distributionalstruc-

O e o ° t Ut ture of bighorn sheep. This view has been sup- *n X a 11 v 4> .0 3 ported by a recent mitochondrial-DNAanalysis av o . e o o I I o . _ of the genetic structure of ewe groups in the 90 t} X =) G) C - o S r Xt,5, o E E E PeninsularRanges (Boyce et al. 1999). U C C U o o r o z X a; X Q 3 n U O 2 O o Q N u 2 LL CL The spatialstructure of populationsis formed *N X z r o < U _ m < 2 _D by discontinuitiesin distributionthat result from t f-U a o o C U U X w t. n Q habitatheterogeneity and biologicalcharacteris- Bighornsheep distributionand abundance * Rubinet al. 547

Table3. Summaryof bighornsheep waterhole-countanalysis, Peninsular Ranges, California. Annual counts were conductedduring 1971-1996(Carrizo Canyon counts were conducted1973-1982).

No. sites No.yr Regression Annual Countregion counted counted coefficient(SE)a percentchange P-valueb

CarrizoCanyon 4-6 10 - 0.0996(0.038) - 9.9 0.03 SouthSan Ysidro Mts. 1-4 26 - 0.0191(0.025) - 1.9 0.46 NorthSan Ysidro Mts. + 0.0105(0.017) + 1.1 0.55 PalmCanyon 1-5 25 + 0.0036(0.019) + 0.4 0.86 HeliholeCanyon 1-4 23 + 0.0076(0.024) + 0.8 0.75 CoyoteCanyon - 0.0262(0.01 1 ) - 2.6 0.02 LowerWillows-Box Canyon 1-2 25 + 0.0294(0.021 ) + 2.9 0.17 MiddleWillows-Salvador Canyon 2-5 26 - 0.0233(0.015) - 2.3 0.14 CougarCanyon-SheepCanyon 1A 26 -0.1305 (0.019) -13.1 0.0002 All SanYsidro Mts. + 0.0007(0.016) + 0.1 0.97 SanYsidro Mts. + CoyoteCanyon - 0.0169(0.007) - 1.7 0.03

aLinear regression of numberof ewes countedeach year(data were transformedto naturallog afterconstant of 0.5 was added). h Null hypothesis:regression coefficient = O. P-valuesshown are basedon randomizationtest, t-testvalues were nearlyidentical. tics of the species (Gilpin 1987). Fragmentationis typi- habitat use (Krausman and Leopold 1986) and in- callyseen as detrimentalto populationviability, but a cer- creased mortality (Cunningham and deVos 1992) in tain degree of fragmentationis an inherentcomponent of other mountain ranges. The apparent lack of move- populationstructure. Although bighorn sheep are able to ment across Highway 74 during our study may have re- cross largetracts of land,the philopatricbehavior of ewes sulted from increased traffic(Calif. Dep. of Transporta- and their associationwith mountainous,open terrainre- tion records [unpubl. data] indicate that traffic has ap- sults in a distributionthat could be considered naturally prox tripled on this road since 1970), a decline in the fragmented(Bleich et al. 1990). We propose, however, number of ewes west of this highway (DeForge et al. that construction and use of roads may have increased 1995), or a combination of these factors. the fragmentationof ewe distributionin the Peninsular The other ewe group boundaries that we identified Ranges. Fourofthe boundariesbetween ewe groupsthat may have resulted from breaks in suitable habitat or we defined coincided with paved roads ighway 74 in loss of ewe groups due to disease, habitat modiElca- the SantaRosa Mountains,road S-22 in the San Ysidro tion, or predation. For example, at the north end of Mountains,Highway 78 between the San Ysidro Moun- the Peninsular Ranges, reduced numbers of bighorn tains and the VallecitoMountains, and road S-2between sheep (DeForge et al. 1995) and the loss of habitat to CarrizoCanyon and the VallecitoMountains; Fig. 2). urban development may have contributed to the ap- It is possible that the section of road S-2 that sepa- parent lack of connectivity betsveen ewes in the San rates ewe groups in CarrizoCanyon and the Vallecito Jacinto Mountains and those in the Santa Rosa Moun- Mountains coincides with a natural topographical tains. The boundary between the Coyote Canyon break, which may promote discontinuity in ewe distri- ewe group and the north San Ysidro Mountains ewe bution (Fig. 2). In contrast, a more southern stretch of group coincides with the loss of bighorn sheep in this road, located in continuous, rugged terrain, was Cougar Canyon and Sheep Canyon revealed in our crossed seasonally by CarrizoCanyon ewes. Similarly, analysis of waterhole count data (Table 3; Appendix road S-3, which was crossed occasionally by ewes in A). The use of off-roadvehicles and livestock grazing the south San Ysidro group, passed through continu- (currently restricted activities) may have contributed ous, rugged terrain. However, other roads that sepa- to this fragmentation and the current absence of big- rated ewe groups (Highway 78, road S-22, and High- horn sheep in Cougar Canyon and Sheep Canyon. way 74) also traversedcontinuous, rugged terrain. We During this study, we did not observe bighorn sheep only observed radiocollared ewes crossing Highway in the mountains directly west of the Vallecito Moun- 78 and road S-22 on 1 and 2 occasions, respectively, tains (the SanvtoothRange, OriflammeMountains, and and never documented ewes crossing Highway 74, al- lower elevations of the LagunaMountains), and we oh though we observed ewes within 50-100 m of these served only 1 ram during our survey of the Fish Creek roads on numerous occasions. Ewes were observed Mountains. Earlystudies suggested that both of these crossing Highway 74 during the 1970s (V. Bleich, areas may have supported "transient" populations Calif.Dep. Fish and Game, pers. commun.). Vehicular (Weaver et al. 1968, Weaver 1972), and single rams traffic has been found to be associated with decreased have been sighted occasionally over the past 25 years 548 WildlifeSociety Bulletin1998, 26(3):53>551

(M.Jorgensen, unpubl. data). Although recent observa- horn Inst., Palm Desert, Calif., 1996), and 19 in the San tions suggest that these areas are used by only a small Jacinto Mountains(DeForge et al. 1997), thus generat- number of rams, ewe groups were observed at the edge ing a combined estimate of 276 bighorn sheep in the of these mountains (southeast edge of the Vallecito United States PeninsularRanges in 1996. South of the Mountains and northwest extent of the Tierra Blanca Santallosa Mountains,our data suggested a short-term Mountains),suggesting that both of these areas may be (2-yr) decline of 24% (P = 0.16) and 28% (P = 0.09) used by ewes under differentclimate conditions or pop- among adults and ewes, respectively. Given the en- ulation sizes. Bighorn sheep use of mountains west of dangered status of bighorn sheep in the Peninsular the Vallecito Mountainsalso may have been restricted Ranges, we believe the use of a significance value of P by livestock grazingand fire suppression. < 0.10 is appropriate. Thus, we concluded that the We did not observe bighorn sheep between Inter- number of ewes had declined significantlyduring this state 8 and the Mexican border, an area that was esti- 2-year (1994-1996) period. Earlierestimates that were mated to be inhabited by >20 bighorn sheep in 1968 generated for this portion of the Peninsular Ranges (Weaver et al. 1968) and 30 bighorn sheep in 1979 could not be directly compared with our estimates be- (Cunningham 1982). Helicopter surveys of this area cause different techniques were used (i.e., waterhole detected only 2 rams in the early 1980s (D. A. Jessup, counts or surveys conducted on foot; Weaver 1972, Jor- unpubl. data) and no bighorn sheep in the mid-1980s gensen and Turner 1973, Jorgensen and Turner 1975, (M. Jorgensen, unpubl. data). It is likely that the con- Weaver 1975). struction of Interstate 8 (a 4-lane freeway) in the mid-1960s, in combination with railroadactivity, live- Long-terrn abundance trends stock grazing, poaching, and fire suppression, con- Our analysis of waterhole count data supported tributed to the disappearance of sheep in this area. the conclusion that bighorn sheep numbers have de- Thus, Interstate 8 and Interstate 10, at the north end clined in selected regions of the Peninsular Ranges of the range, effectively isolate bighorn sheep in the outside of the Santa Rosa Mountains (Table 3; Figs. 1 United States Peninsular Ranges. Bighorn sheep and 2). However, not all areas covered by the water- movement into the San Bernardino Mountains to the hole counts exhibited a decline. For example, our north and into Mexico to the south may have been analysis suggested that the number of bighorn sheep limited even before freeway construction. However, has declined in Coyote Canyon, but remained rela- it is likely that these freeways and associated habitat tively stable in the north and south San Ysidro Moun- modification (e.g., fencing and urban development) tains during the past 26 years Furthermore, the de- have further restricted any such movements. cline in Coyote Canyon was caused largely by the loss of sheep in one portion (Cougar and Sheep Canyons) Abundance and recent population of this large canyon (Table 3; Appendix A). trends These results emphasize the importance of scale Increased fragmentationcan reduce population size and resolution when assessing population parameters (Burgman et al. 1993) and effective population size such as abundance and trends. For instance, if data (Gilpin 1987), thereby increasing the risk of extinction from the 2 San Ysidro regions were combined with (Gilpin and Soule 1986). From our 1994 survey data, data from Coyote Canyon, it would appear that a sig- we estimated that the population size (rams and ewes nificant (P = 0.03) decline had occurred throughout combined) in the United States PeninsularRanges, ex- this region (Table 3). This effect, however, would be cluding the SantaRosa and SanJacinto Mountains,was primarily due to the data from Cougar and Sheep 214.2 + 64.4, with the largest single group consisting of Canyons. The decline in the number of ewes counted approximately68 individualsJable 2). A survey of the in Cougar and Sheep Canyons was accompanied by a Santa Rosa Mountains conducted in 1994, using tech- positive, but statistically nonsignificant (P = 0.17), niques similarto ours, generated an estimate of 115.5 + trend in the number of ewes counted in the Lower 24 adult bighorn sheep (DeForge et al.1995). The San Willows-Box Canyon area. This could be the result of Jacinto Mountains were believed to support an addi- a shift in habitat-usepatterns; however, the loss of big- tional 17 bighorn sheep (DeForge et al. 1997). The es- horn sheep in 1 portion of Coyote Canyon was ac- timated population of bighorn sheep in the United companied by an overall significant decline in num- States Peninsular Ranges was, therefore, 347 in 1994. bers in this canyon. Cougar and Sheep Canyons are Surveys conducted in 1996 produced bighorn sheep located between the north San Ysidro and Coyote population estimates of 163.0 + 31.2 south of the Santa Canyon ewe populations, and we could have assigned Rosa Mountains,93.8 + 22 in the SantaRosa Mountains waterhole count data from this area to the San Ysidro d. R. DeForge and S. D. Ostermann, unpubl. data, Big- Mountains region rather than to Coyote Canyon. A1- Bighornsheep distributionand abundance * Rubinet al. 549 though we do not know what pattern of home-range slightly over time, in response to habitat and resource connectivity existed between ewes in Coyote Canyon availability. We identified a recent decline in the num- and ewes in the north San Ysidro Mountains in the ber of ewes in areas outside of the SantaRosa and San pastSwe treated Cougar and Sheep Canyons as a part Jacinto Mountains. Within our study area} some, but of Coyote Canyon because these sites are geographi- not all, ewe groups exhibited long-termdeclines. This cally closer to areas currently used by ewes in Coyote suggests that ewe groups may have been influenced by Canyon, and the canyons drain into Coyote Canyon. different factors and, thus, face different extinction The analysis of waterhole count data collected in risks. Recently, a regional approach to bighorn sheep Coyote Canyon and in Carrizo Canyon provides evi- management has been promoted (Torres et al. 1994, dence that local declines in numbers of bighorn Bleich et al. 1996), emphasizing the concept of bighorn sheep have occurred. In the Santa Rosa Mountains? sheep metapopulations, first proposed by Schwartz et DeForge et al. (1995) documented an adult popula- al. (1986). We suggest that the most effective conser- tion decline of 69% during a 12-year period vation tactics will be those that make use of this re- (1983-1994). When these authors divided their sur- gional approach, while simultaneouslyconsidering the vey area into 3 geographical sampling units, it was identity and dynamics of the individual ewe groups. found that a decline was evident in all 3 areas) with Comparisons of individual ewe groups may provide similar declining trends in 2 sampling units and a valuable insight into the apparent differences in local slower decline in the third sampling unit (Santa Rosa abundance trends, because differentinfluences may be Mountains-west of Highway 74), the only location in acting on differentewe groups. Trends should be mon- the Peninsular Ranges where the population has itored (via helicopter surveys and waterhole counts) been augmented with captive-born animals (DeForge throughout the PeninsularRanges to assess and direct et al. 1995). Additional analysis of their survey data? management efforts. At a regional level, potential incorporating ewe group boundaries suggested in connectivity between ewe groups must be main- our study, would be especially valuable in under- tained through habitat protection (Schwartz et al. standing these regional trends. 1986, Bleich et al. 1990). A multi-scale approach such The analysis of waterhole count data revealed varia- as this may provide the greatest insight into the factors tion in trends among ewe groups?suggesting that the de- that influence the viability of bighorn sheep in the mographicdynamics in these groups were independent PeninsularRanges; such insight will enhance the devel- and that ewe groups may be influenced by local as well opment of effective management decisions. as landscape-scale factors. Winter precipitation has been found to be associated with lamb recruitmentin Acknowledgments. This study was funded by the the following year (X)ouglasand Leslie 1986, Wehausen CaliforniaDepartment of Fish and Game, the California et al. 1987) and thereby has the potentialto influence the Department of Parks and Recreation,the Pew Charita- number of ewes counted 1.5 years later. However, we ble Trusts, the EducationalFoundation of America,the found no relationship between the number of ewes Zoological Society of San Diego, and the Anza-Borrego counted and precipitationduring winter months in the Desert NaturalHistory Association. We thankJ. Allen, year preceding the count, nor with precipitationduring V. Bleich, R. Botta,R. Clark,T. Evans,R. Mouton,J. We- the 3-monthperiod preceding the count. We also found hausen, arldall those who helped with field data collec- that the number of ewes counted was not consistently tion and waterhole count surveys. In addition, we are correlatedwith the high temperatureduring each count. gratefulfor the assistanceand cooperation of the Bureau These findings suggested that other, local influences of Land Management, the Bighorn Institute, Landell's (specific to ewe groups), e.g., habitatquality, predation, Aviation, the Zoological Society of San Diego, and the or disease, may be more importantthan the effects of cli- University of CaliforniaBoyd Deep Canyon Desert Re- mate. Dunng our study we found that predation by search Center duringvarious phases of this study. mountain lions was common and appeared to fluctuate among ewe groups and among years. Predation may have been responsible, in part, for vanation in the dy- Literature cited namics of individualewe groups. BLEICH,V. C.,J. D. WEHAUSEN,AND S. A. HOLL.199(). Desert-dwelling We conclude that bighorn sheep in the Peninsular mountain sheep: conservation implications of a naturally frag- Ranges are currently distributed in multiple ewe mented distribution. Conservation Biology 4:383-390. groups. This distributionalpattern may be influenced BLEICH,V. C.,J. D. WEHAUSEN,R. R. RAMEYII, ANDJ.L. RECHEL.1996. Metapopulation theory and mountain sheep: implications for by the abundance of bighorn sheep and may, therefore, conservation. Pages 353-373 i7 D. R. McCullough, editor. be altered if population size increases or decreases. Metapopulations and Wildlife Conservation. Island Press, Furthermore,the distributionof ewe groups may shift Washington, D.C. 550 WildlifeSociety Bulletin1998, 26(3):53s551

BOYCE,M. S. 1992. Population viability analysis. Annual Review of GILPIN,M., ANDM. SOULE.1986. Minimum viable populations: Ecology and Systematics 23:481-506. processes of species extinction. Pages 19-34 in M. Soule, edi- BOYCE,W. M., P. W. EIEDRCK,N. E. MUGGLI-COCKEFr,S. KALINOWSKI, tor. Conservation Biology: The Science of Scarcity and Diver- M. C. T. PENEDO,AND R. R. RAMEYII. 1997. Genetic variation of sity. Sinauer Associates, Inc., Sunderland, Massachusetts. major histocompatibility complex and microsatellite loci: a HANSKI,I., ANDM. GILPIN.1991. Metapopulation dynamics: brief comparison in bighorn sheep. Genetics 45 421-433. history and conceptual domain. Biological Journal of the Lin- BOYCE,W. M., R. R. I{AMEYII, T. C. RODWELL,E. S. RUBIN,AND 1t. S. nean Society 42:3-16. SINGER.1999. Population subdivision among desert bighorn HATFIELD,J. S., W. R. GOULDIV, B. A. HOOVER,M. R. FULLER,AND E. L. sheep (Ovis canadensis) ewes revealed by mitochondrial DNA LINDA2UIST.1996. 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Uni- Anza-Borrego Desert State Park. Desert Bighorn Council versity of CaliforniaPublication in Statistics 1(7):131-160. Transactions 19:51-53. COLLINS1B. T. 1990. Using rerandomization tests in route-regres- KIE,J. G., J. A. BALDWIN,AND C. J. EVANS.1994. CalHome Home sion analysis of avian population trends. Pages 63-70 in J. R. Range Analysis ProgramUser's Manual. U.S. Forest Service, Pa- Sauer and S. Droege, editors. Survey Designs and Statistical cific Southwest Research Station, Presno, California. Methods for the Estimation of Avian Population Trends. U.S. KRAUS^rAN,P. R., ANDB. D. LEOPOW.1986. The importance of small Fish and Wildlife Service, Biological Report 90(1). populations of desert bighom sheep. Transactionsof the North CUNNINGHAM,S. C. 1982. Aspects of the ecology of Peninsulardesert AmericanWildlife and NaturalResource Conference 51:52-61. bighorn sheep (Ovis canadensis cremnobates) in Carrizo MANLY,B. F. J. 1991. 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Assessing rates of in- actions 38:17-28. crease from trend data. Journal of Wildlife Management TURNER,J. C., AND3. B. PAYSON.1982. The occurrence of selected 56:603-610. infectious diseases in the desert bighorn sheep, Ovis canaden- FEsTA-BIANcHET,M. 1991. The social system of bighorn sheep: sis cremnobates, of the Santa Rosa Mountains, California. Cali- grouping patterns kinship and female dominance rank. Ani- fornia Fish and Game 68:235-243. mal Behavior 42:71-82. WEAVER,R. A. 1972. Conclusions of the bighorn investigation in GEIST,V. 1971. Mountain sheep: a study in behavior and evolu- California. Desert Bighorn Council Transactions 16:56-65. tion. The University of Chicago Press, Chicago, Illinois. WEAVER,R. A. 1975. Status of the bighorn sheep in California. GILPIN7M. 1987. Spatialstructure and population vulnerability. Pages Pages 58-64 in J. B. Trefethen, editor. The Wild Sheep in Mod- 125-140 in M. Soule, editor. Viable Populations for Conserva- ern North America. 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Bighornsheep distributionand abundance * Ftubinet alz 551

Desert Bighorn Council Transactions 33:11-12. _ [ cludes Anza-Borrego Desert WEAVER,R. A., J. L. MENSCH,AND W.V. FAIT. 1968. A survey of the _ ^ StatePark. Steve G. Torresis a California desert bighorn (Ovis canadensis) in San Diego _5i. ' D seniorwildlifebiologistwiththe County. California Department of Fish and Game, i: 2 _ CaliforniaDepartment of Fish Pittman-Robertson Project W-5 1 -R- 14. _ 511 and Game ar d is responsible WEHAUSEN,J. D., V. C. BLEICH,B. BLONG,AND T. L. RUSSI. 1987. Re- _2 " - forthe managementof bighorn cruitment dynamics in a southern California mountain sheep w . w sheepand mountain lions in the population. Journal of Wildlife Management 51:86-98. w . } \ E state. CharlesL. Hayes is now a WILCOVE,S. D., C. H. McLELLAN,ANDA. P. DOBSON.1986. Habitatfrag- f :u:<:K8 \ -E. / \ biologistwith the New Mexico mentation in the temperate zone. Pages 237-256 in M. E. Soule, *- :. - . :; X - - 8 editor. Conservation Biology: The Science of Scarcit,v and Diver- L. a De,oartmentof Game and Fls

sity. Sinauer Associates, Inc., Sunderland, Massachusetts. x2Xq 1lll 1 = _ managementofmountatn lionE

EstherS. Rubin(photo) is a Ph.D.candidate in the GraduateGroup in ico. Chantal S. O'Brien is Ecologyat the Universityof California,Davis. Her dissertationfo- _ workingon wildlifeprojects in cuseson Peninsularbighorn sheep, and she is currentlyhelping to de- Arizonaand is consideringad- velopa recoveryplan for this federally endangered population. Wa/- _ vancedgraduate work in wild- ter M. Boyce is a professorand wildlifeveterinarian at the Wildlife life biology. DavidA. Jessupis HealthCenter at the Universityof California,Davis. MarkG Jor- a wildlifeveterinarian with the CaliforniaDepartment of Fishand gensenis a resourceecologist for the ColoradoDesert District of Cal- Gameand is now workingextensively with marine species.

AppendixA. Mean numberof bighornewes countedper day (x) duringannual waterhole counts and numberof count sites (n) in the PeninsularRanges, California, 1971-1996.

Coyote Canyon

Middle North San Ysidro Mts. Cougar- Lower Willows- Sheep Willows- Salvador Palm Helihole SouthSan Carrizo Canyons Box Canyon Canyon Canyon Canyon Ysidro Mts. Canyon

Yr x n x n x n x n x n x n x n

1971 5.67 3 3.33 2 4.33 2 0.00 1 1.67 2 1972 6.67 2 3.33 2 7.50 2 10.33 4 3.33 1 1973 3.67 1 15.00 2 6.33 1 7.33 1 15.83 6 1974 3.83 3 6.33 l 9.83 3 7.00 2 3.00 2 4.17 2 18.17 6 1975 8.00 3 0.00 1 6.33 3 15.67 4 2.00 1 1.33 2 26.50 6 1976 10.83 3 2.17 1 7.83 3 2.67 3 1.67 2 31.83 6 1977 10.67 3 2.00 1 5.17 2 0.50 3 1.67 1 0.50 2 20.00 6 1978 2.33 3 1.67 1 8.33 3 3.00 2 1.67 1 5.00 2 15.33 4 1979 11.00 4 3.83 2 14.83 5 8.33 4 1.00 2 5.50 2 15.33 6 1980 3.00 2 0.00 2 23.00 3 1.33 4 0.00 3 5.67 2 6.83 6 1981 0.00 3 1.83 1 2.50 2 9.33 3 0.00 1 6.33 3 1 1.00 6 1982 0.33 4 0.67 2 10.67 4 5.67 3 0.33 4 0.00 2 9.83 6 1983 0.17 4 3.83 2 4.67 4 9.67 4 0.00 1 1.83 3 1984 0.33 4 3.83 2 2.83 4 7.00 4 0.33 3 6.83 3 1985 0.67 4 1.33 2 6.33 5 14.00 4 0.00 2 8.50 4 1986 0.00 4 1.67 2 6.67 3 7.00 4 0.00 2 6.17 3 1987 0.00 4 0.67 2 12.00 4 5.50 5 1.50 2 0.00 3 1988 0.00 3 4.67 2 1.00 4 10.67 4 1.33 1 6.33 3 1989 1.33 3 1.67 2 8.33 4 11.00 4 0.67 2 7.67 3 1990 0.00 3 1.67 2 5.67 4 8.00 4 1.33 2 8.00 3 1991 0.00 3 7.67 2 7.00 2 9.67 4 0.00 1 0.33 3 1992 0.33 3 6.67 2 5.67 4 9.33 4 0.00 2 0.33 3 1993 0.00 3 9.33 2 2.00 4 7.33 5 0.00 1 0.33 3 1994 0.00 3 7.00 2 3.67 4 6.67 4 2.33 2 3.33 2 1995 0.00 4 3.67 2 9.00 5 4.67 5 1.67 1 0.67 3 1996 0.00 3 1.33 2 6.00 3 1.00 4 4.67 2 4.67 3

AssociateEditor: Jacobson