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bucnar West — Our Uvin^ Resources 



Bighorn Sheep 

 in the Rocky 

 Mountain 

 National Parks 



by 



Francis Singer 



National Biological Service 



50- 



25 



■ft 



ndiqenoub Dilulion 



founder translocation 



Single >1 -2 



founder Supplement Sources 

 same source 



50- 



42 



25 





1 2 



No. of supplemental translocations 



<16km 16 -32 km >32km 

 Distance to domestic siieep 



Figure. Factors contributing to 

 persistence of bigliom slieep trans- 

 locations. The numbers above tfie 

 bars refer to llie total number, or 

 sample size, of populations in that 

 category. 



Ciinent numbers of bighorn sheep {Ovis 

 ciiiuich'iisis) are probably only 2%-8% of 

 their numbers at the time of European settle- 

 ment. The Rocky Mountain subspecies {O.c. 

 camulcnsis) and the California subspecies {O.c. 

 califomiana) combined may have numbered 

 roughly 1 million, and the desert subspecies 

 {O.c. nc'Isoni) of the southwestern United States 

 and Mexico also likely numbered about 1 mil- 

 lion (Buechner 1960: Wishart 1978; Bleich et 

 al. 1990). Unregulated harvesting, habitat 

 destruction, overgrazing of rangelands. and dis- 

 eases contracted from domestic livestock all 

 contributed to drastic declines, the most drastic 

 occurring from about 1870 through 1950. 



Bighorn exist mostly in small, isolated pop- 

 ulations within their former vast range. Thome 

 et al. (1985) found that b49c of 166 populations 

 in the western United States contained fewer 

 than 100 individuals. In Arizona, 88% of the 

 populations (52 of 59) contained fewer than 100 

 individuals (Krausman and Leopold 1986). 



Small populations of animals may be at 

 higher risk of extirpation (Gilpin and Soule 

 1986). The negative effects of small population 

 size on bighorn were documented by Berger 

 ( 1990). who reported that no indigenous popu- 

 lations of fewer than 50 animals survived for 5 

 decades, whereas all populations numbering 

 more than 100 animals survived for the same 

 period. Berger's (1990) published review did 

 not consider national park populations of 

 bighorns. 



Restoration of bighorn sheep has been pur- 

 sued actively by many state and federal agen- 

 cies since the I940"s. although these efforts 

 have met with only limited success, and most of 

 the historical range of bighorns remains unoc- 

 cupied. Human encroachments near bighorn 

 populations are severe enough in some areas 

 that the peninsular population of desert 

 bighorns in California has been proposed for 

 federal threatened status. 



This article reviews the status of bighorns of 

 three subspecies, the desert. Rocky Mountain, 

 and badlands (O.c. audohonii). in 17 national 

 park service units in the Rocky Mountains. 

 Factors contributing to the success of 1 15 trans- 

 plants of bighorn sheep that occurred over the 

 past five decades in six Rocky Mountain states 

 are also reviewed. 



Information on the status and restoration of 

 bighorns in the National Park Service units 

 came from published accounts, university the- 

 ses, unpublished park records, and a question- 

 naire mailed to state wildlife agencies and land 

 managers in Colorado, Montana. North and 

 South Dakota. Wyoming, and Utah. Only popu- 

 lations that had been translocated at least 10 

 years were included in the analysis. 



Status in National Parks 



Eighteen national park units historically 

 contained populations of bighorn sheep. Native 

 populations of bighorns were extirpated in all 

 but five of the units, and populations were great- 

 ly reduced in four of these five. Only the 

 Yellowstone's ranges remained fully occupied 

 by bighorn during this period. Native bighorns 

 survived but were greatly reduced in Grand 

 Teton, Canyonlands, Glacier, and Rocky 

 Mountain parks. The Badlands subspecies was 

 eliminated about 1921. This subspecies origi- 

 nally inhabited clay badlands and low river 

 breaks in the Dakotas, including Badlands and 

 Theodore Roosevelt national parks. 



Restoration efforts of bighorns into park 

 units began in the late 1940"s in 11 national 

 park units where bighorns had been extiipated. 

 Augmentations or translocations of additional 

 subpopulations occurred in three of five nation- 

 al park units where bighorns had not been com- 

 pletely extirpated. Bighorn ranges are now con- 

 sidered fully or very fully occupied in two of 

 these units. Rocky Mountain and Canyonlands 

 parks. 



Restoration of bighorns into other national 

 park units has had only limited success. Ten 

 national park units support persisting popula- 

 tions (numbering 100 or more sheep the previ- 

 ous 4 years): five park units have populations 

 estimated to exceed 500 animals: and five other 

 park units have populations of 100-200. Five 

 other park units have fewer than 100 individu- 

 als, and two of these units support populations 

 on the verge of extirpation (only 6-14 animals). 



Translocations 



Only 39% of 115 bighorn transplants in six 

 Rocky Mountain states were rated as persisting 

 (Figure). Sixty-four percent of transplants locat- 

 ed more than 32 km (20 mi) from domestic sheep 

 were persistent, but only 44% of those bighorn 

 populations located 16 to 32 km from domestic 

 sheep were persistent (Figure). In addition, near- 

 ly twice as many transplanted populations that 

 were sedentary failed than populations that 

 migrated to separate winter and summer ranges. 

 Most translocated populations do not regain the 

 historical migration patterns of the extirpated 

 native population: instead, many spend the sum- 

 mer and winter on the same small ranges. 



Limited evidence suggests that threshold 

 population size or genetic diversity is related to 

 persistence of bighorn transplants. Transplant 

 persistence and genetic diversity were positive- 

 ly correlated to initial founder group size (the 

 number of animals moved in the initial translo- 

 cation), to multiple (versus single) source 



