Rocky Mountain Bighorn Sheep (Ovis Canadensis): a Technical Conservation Assessment

Rocky Mountain Bighorn Sheep (Ovis canadensis): A Technical Conservation Assessment Prepared for the USDA Forest Service, Rocky Mountain Region, Species Conservation Project February 12, 2007 John J. Beecham, Ph.D., Cameron P. Collins, M.S., and Timothy D. Reynolds, Ph.D. TREC, Inc. 4276 E. 300 North Rigby, Idaho 83442 Peer Review Administered by Society for Conservation Biology Beecham, J.J. Jr., C.P. Collins, and T.D. Reynolds. (2007, February 12). Rocky Mountain Bighorn Sheep (Ovis canadensis): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/rockymountainbighornsheep.pdf [date of access]. ACKNOWLEDGMENTS We thank the following biologists from the states of Colorado (Bruce Watkins), Wyoming (Doug McWhirter, Doug Brimeyer, Greg Anderson, Gary Fralick, Dean Clause, Stan Harter, and, especially, Kevin Hurley), South Dakota (Ted Benzon), and Nebraska (Gary Schlichtemeier and Dustin Darveau); and from the national forests within USDA Forest Service Rocky Mountain Region for their time and willingness to provide information for this species assessment of the status of Rocky Mountain bighorn sheep. We are particularly grateful to Idaho Department of Fish and Game biologists Dale Toweill and Frances Cassirer for their thoughtful reviews of early drafts of the document and to Jon Jorgenson (Alberta Fish and Wildlife) and an anonymous reviewer for helpful comments on the final draft. We thank Patricia Isaeff for assembling the envirogram into a useful display format, Jarod Blades for constructing many of the sheep-distribution figure, and Brandt Elwell for his quick and successful resolution of GIS imagery issues. Finally, the authors thank Gary D. Patton, Species Conservation Project Manager, and Melanie Woolever, Wildlife Program Manager, both with the USDA Forest Service Rocky Mountain Regional Office, for their guidance, direction, and patience. The authors are in debt to Ms. Kimberly Nguyen, Technical Specialist, for her help and patience in developing the final Web published product. AUTHORS’ BIOGRAPHIES John Beecham received his Ph.D. from the University of Montana in 1980, his M.S. from the University of Idaho in 1970, and his B.S. from Texas Tech University in 1968. He retired in 1999 after 29 years of working as a research biologist and manager for the Idaho Department of Fish and Game (IDFG). John conducted field research on black bears for 12 years before moving into the headquarters office to manage IDFG’s research program and their statewide management programs for black bears, cougars, moose, bighorn sheep, and mountain goats. As the program manager for IDFG’s bighorn sheep program, John was IDFG’s management level representative on the multi-state Hells Canyon Bighorn Sheep Initiative project from its inception until his retirement in 1999. John also directly supervised the field activities of the bighorn sheep research biologist assigned to the project. John went to work for the Hornocker Wildlife Institute and the Wildlife Conservation Society (WCS) after retiring from IDFG, where he supervised their research efforts in the Greater Yellowstone area on wolverines, black bears, and cougars. John left WCS in 2003 and continues to work as a wildlife consultant on a variety of projects. Cameron P. (Cam) Collins received his M.S. (Wildlife Resources) in 2004 from the University of Idaho and his B.S. (Terrestrial Ecology) in 1995 from Western Washington University. His master’s research investigated the ecology of Columbian sharp-tailed grouse associated with reclaimed mined lands and native shrub-steppe in Colorado. He has participated in a reintroduction program for the Hawaiian crow, and an investigation of the status of the Hawaiian hawk for the U.S. Fish and Wildlife Service. He has also spent time on research projects with northern goshawks and northern spotted owls, was part of an effort to eradicate feral ungulates from Santa Catalina Island, and has produced a similar conservation assessment for the ferruginous hawk. He is currently conducting a radio-telemetry study to investigate the effects of wind power development on the ecology of greater sage-grouse in southeastern Idaho for TREC, Inc. Timothy D. (Tim) Reynolds is President and owner of TREC, Inc., a Service-disabled, Veteran-owned, consulting firm specializing in environmental services and ecological research in Rigby, Idaho. He received his Ph.D. in Zoology (Ecology emphasis) from Idaho State University in 1978 and his M.S. (Biology) and B.S. (Biology, Comprehensive) from Illinois State University in 1974 and 1972, respectively. During his career he has been a Visiting Professor of Biology at Boise State University, Radioecologist for the U.S. Department of Energy, and a Research Ecologist and Director of Operations for the Environmental Science and Research Foundation. He has conducted and 2 3 coordinated ecological research on birds, mammals, reptiles, and ecological aspects of hazardous waste management, and selenium inventories of soils and vegetation on selected bighorn sheep winter ranges in Idaho. He has nearly 50 publications in the technical literature. COVER PHOTO CREDIT Rocky Mountain bighorn ram (Ovis canadensis canadensis), Rocky Mountain National Park, Colorado. © Jesse Speer Photography. Used with permission. 2 3 SUMMARY OF KEY COMPONENTS FOR CONSERVATION OF THE ROCKY MOUNTAIN BIGHORN SHEEP Two species of mountain sheep occur in western North America. Thinhorn mountain sheep (Ovis dalli) are found in Alaska and the Yukon, Northwest Territories, and British Columbia in Canada. The bighorn species (O. canadensis) was historically distributed from the Canadian provinces of British Columbia and Alberta south to Mexico. Rocky Mountain (O. c. canadensis) and a desert subspecies (O. c. nelsoni) of bighorn sheep are found within USDA Forest Service Region 2. This conservation assessment focuses on the Rocky Mountain bighorn sheep within Region 2. Minimal human impacts and the remoteness of thinhorn mountain sheep habitat have resulted in relatively stable populations across their range. However, from the late 1800’s through the mid-1900’s, bighorn sheep populations experienced significant declines across their range as a result of diseases introduced from domestic livestock, unregulated and market hunting, habitat loss, and competition from domestic livestock. In the 1960’s, many western states, including those in Region 2, began active bighorn sheep transplant programs in an effort to augment small, remnant sheep populations and to reintroduce bighorns into historic, but vacant, habitat. Although bighorn sheep numbers increased throughout the western United States because of these transplant efforts, periodic die-offs continued to occur in many herds, including those in Region 2. These die-offs appeared to result from transmission of pneumonia pathogens from domestic sheep (Ovis spp.), possibly in conjunction with environmental stressors. Threats to the long-term viability of bighorn sheep in Region 2 include diseases transmitted by domestic livestock, the lack of connectivity and/or loss of genetic variability (fitness) due to habitat fragmentation, habitat loss, increased human disturbance, competition with domestic livestock, and predation on small, isolated herds. The relative importance of these threats to the persistence of bighorn sheep in Region 2 varies from area to area. However, the risk of disease outbreaks resulting from contact with domestic sheep and goats is widely believed to be the most significant threat facing bighorns in Region 2 and elsewhere across their range. Despite these risks to population persistence, several areas can be considered strongholds for bighorns in Region 2. As evidenced by a history free of disease-related die-offs, these areas have a minimal risk of disease outbreaks, or if die-offs have occurred, the suspected causes (i.e., domestic sheep or goat herds) have been removed or significantly lessened. In addition, the individual bighorn populations in these areas are relatively large and exhibit a functioning metapopulation structure, ensuring a significant degree of genetic exchange among herds. Finally, habitat quality is not a limiting factor in terms of imposing impediments to seasonal migration or leading to poor herd health due to nutritional deficiencies. Obvious strongholds within Region 2 are found in northwestern Wyoming and south-central Colorado. Herd units in these two areas are well connected, allowing movement between populations; consist of some of the largest populations within Region 2; are free of disease-related die-offs; and occupy habitats where the threat of domestic sheep contact has been removed or dramatically reduced. Seasonal movements are not greatly impaired in these two areas, and habitat quality is not a limiting factor. Several bighorn herds in Region 2 are at risk of extirpation from disease-related die-offs and/or chronically poor production, small population size, total or near complete isolation from other bighorn populations, major obstacles to seasonal movements, and poor habitat quality leading to poor nutrition. Most of these units are located in southwestern Colorado, but additional high-risk areas include South Dakota’s Custer State Park population and all three herds in Nebraska. A large number of bighorn herds in Colorado and Wyoming possess both low- and high-risk characteristics. Because these herd units face fewer total threats, or less dire threats,

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