Our Living Rcxaiovtw — Interior Wi'sl 



.?.?.? 



populations represented in the initial toiindcr 

 group, to tiie use of native populations as a 

 source, and to sheep interaction with other near- 

 by subpopulations (Fitzsimrnons 1992). 



Implications 



Restorations into national park units are. as 

 yet, incomplete. At present, bighorn sheep occur 

 in small, widely scattered populations, with the 

 smallest groups (fewer than 50 animals) seem- 

 ingly at highest risk of extirpation. Thus, to 

 achieve larger, more secure populations, restora- 

 tion is necessary. To improve the chances for 

 successful translocations, greater care must be 

 taken; only about one-third of past transloca- 

 tions were persistent. Our analysis suggests that 

 a population distant from domestic sheep 

 improved the probability of its persistence more 

 than any other factor. Larger founder sizes, mul- 

 tiple versus single sources of founders, native 

 source groups, interactions with nearby subpop- 

 ulations. and migratory tendencies also may 

 contribute to continued persistence of translo- 

 cated sheep and should be considered during 

 translocations. Habitat suitability assessments 

 before translocations would also probably con- 

 tribute to sheep restoration success and are rec- 

 ommended as an integral part of any restoration. 



References 



Berger, J. [990. Persistence of difl'erent-sized popii lilt ions : 

 an empirical assessment of extinction in liigliorn popula- 

 tions. Conservation Biology 4:9 1 -^X. 



Bleicti. V.C.. J.D. Weytiausen. and S.A. Holl. I')9t). Desert- 

 dwelling mountain sheep: conservation implications of a 

 natural!)' fragmented distribution. Conservation Biology 

 4:383-390. 



Buechner, H.K. 1960. The bighorn sheep in the United 

 States, its past, present and future. Wildlife Monograph 

 4. 174 pp. 



Fit/simmons, N. 1992. Genetic factors, population histo- 

 ries, and hom growth in Rocky Mountain bighorn sheep. 

 M.S. thesis. University of Wyomuig, Laramie. 76 pp. 



Gilpin, M.E.. and M.E. Soule. 1986. Mniimum viable pop- 

 ulations. Pages 19-34 in M.E. Gilpin and M.E. Soule, 

 eds. Conservation biology, the science of scarcity and 

 diversity. Sinauer Association, Inc., Sunderland. MA. 



Krausman, PR., and B.D. Leopold. 1986. The iinportance 

 of small populations of bighorns. Transactions North 

 American Wildlife and Natural Resources Conference 

 .';i:.';2-61. 



Thome. E.T.. W.O. Hickey. and S.T. Stewart. I98.'i. Status of 

 California and Rocky Mountain bighorn sheep in the 

 United States. Pages 56-81 in M. Hoefs. ed. Wild sheep: 

 distribution and inanagement and conservation of sheep 

 in the world and closely related mountain ungulates. 

 Special Report. Northern Wild Sheep and Goat Council. 

 Whitehorse. Yukon. 



Wishart. W. 1978. Bighorn sheep. Pages 161-171 in J, L. 

 Schmidt and D.L, Gilbert, eds. Big game of North 

 America. Stackpole Books. Harrisburg. PA. 



For further information: 



Francis Singer 

 National Biological Service 

 Natural Resource Ecology 



Laboratory 

 Colorado State University 

 Fort Collins. CO 80.523 



Desert bighorn sheep (Oris caiuulenxis spp.) 

 are subspecies of concern in the continen- 

 tal United States. Populations declined drasti- 

 cally with European colonization of the 

 American Southwest beginning in the l.'iOO's 

 (Buechner I960). At present, deseil bighorn 

 numbers are extremely low, although the overall 

 population trend has increased since 1960. 



Desert bighorn are considered good indica- 

 tors of land health because the species is sensi- 

 tive to many human-induced environmental 

 problems (McCutchen 1981). In addition to 

 their aesthetic value, desert bighorn are consid- 

 ered desirable animals by hunters. 



The Rocky Mountain and California races of 

 bighorn occupy the cooler western and north- 

 western regions of the United States. In con- 

 trast, the desert sheep races are indigenous to 

 the hot desert ecosystems of the Southwest. 



Population Trends 



The number of desert bighorn in North 

 America in pristine times is unknown but most 

 likely was in the tens of thousands (Buechner 

 1960). Seton (1929) estimated the pre- 

 Columbian numbers of all subspecies of 

 bighorn in North America (United States, 

 Canada, and Mexico) at 1.5-2 million. By 

 1960, however, the overall bighorn population 



in the United States, including desert bighorns, 

 had dwindled to 15,000-18,200 (Bu'echner 

 I960). Buechner documented major declines 

 from the 1850"s to the early 1900"s. These 

 declines were attributed to excessive hunting; 

 competition and diseases from domestic live- 

 stock, particularly domestic sheep; usurpation 

 of watering areas and critical range by human 

 activities; and human-induced habitat changes 

 (Buechner 1960: Graham 1980; McCutchen 

 1981). 



These declines were followed by a period of 

 population stabilization that Buechner ascribed 

 to conservation measures. The decline of desert 

 bighorn probably niirroied the pattern of 

 decline of the overall bighorn population. 

 Desert bighorn population trends have been 

 upward since the 1960's when Buechner (1960) 

 estimated their population at 6.700-8.100. In 



Desert 

 Bighorn Sheep 



by 



Henry E. McCutchen 

 National Biological Service 



Desert bighorn sheep (Ovis 

 canadensis nelsoni). 



