Sierra Nevada Bighorn Sheep

• Recovery Program
• Natural History
• Yosemite Bighorn

Related Links

• Sierra Nevada Bighorn Sheep Foundation
• U.S. Fish and Wildlife Service (Sierra Nevada Bighorn Sheep)

Sierra Nevada Bighorn Sheep Recovery Program

Bighorn sheep (Ovis canadensis) are divided into three distinct subspecies based on recent morphometric and genetic evidence. Two of these subspecies are found in California, Sierra Nevada bighorn (O. c. sierrae) and desert bighorn (O. c. nelsoni) see map (PDF). Sierra Nevada bighorn have the most restricted range and the fewest individuals of any bighorn subspecies. CDFW has been the lead agency for implementation of the recovery of Sierra Nevada Bighorn Sheep since 1999. The Sierra Nevada Bighorn Sheep Recovery Program is specifically charged with implementing the recovery of Sierra Nevada Bighorn Sheep, one of the rarest of large mammals in North America. Additionally, CDFW is involved in the conservation and recovery of desert bighorn sheep in the Peninsular Ranges, which are also listed under the Endangered Species Act. CDFW also manages the remaining desert bighorn sheep in California, a program that includes hunting where populations are healthy, and can tolerate some harvest.

Historically, bighorn sheep were distributed along the crest of the Sierra Nevada in California, from Sonora Pass in the north, to Olancha Peak in the south. Prior to European settlement, it has been estimated that there were more than 1,000 bighorn sheep in the Sierra Nevada. However, the Sierra bighorn population was severely reduced during the 19th and 20th centuries apparently because of diseases from domestic sheep, forage competition with domestic livestock, and market hunting. By late 1970s, there were only two geographic areas where bighorn sheep were found (in the vincinity of Mt. Baxter and Mt. Williamson), with a combined population of 250. Between 1979 and 1988, CDFW translocationed bighorn sheep from the Mt. Baxter area to Wheeler Ridge, Mt. Langley, and the Mono Basin to re-establish herds in historic ranges. These recovery efforts were thwarted by another major population decline during the 1990s, attributed primarily to mountain lion predation and drought. By 1995 only about 100 bighorn sheep remained in the Sierra Nevada. Sierra Nevada Bighorn Sheep have been listed under the California Endangered Species Act (CESA) since 1974 but were uplisted from threatened to endangered in 1999 by the California Fish and Game Commission. In the same year, the United States Fish and Wildlife Service (USFWS) temporarily listed them as endangered on emergency basis under the U.S. Endangered Species Act (ESA). Final listing as endangered occurred early in 2000. CDFW was identified as the lead agency for Sierra Nevada bighorn sheep recovery implementation. A recovery team was then assembled, and a recovery plan was drafted.

Federal endangered status was sought for these sheep because of a dangerously low population size and the inadequacy of existing regulatory mechanisms relative Two concerns were identified: negative effects of mountain lion predation and the threat of a major respiratory disease epizootic that could result from contact with domestic sheep grazed on public lands adjacent to bighorn sheep ranges. The Sierra Nevada Bighorn Sheep Recovery Plan (PDF) for Sierra Nevada Bighorn Sheep identified 16 historic herd units and grouped those into 4 recovery units. It specified herd units that needed to be occupied as well as minimum numbers of females by recovery unit necessary for downlisting and delisting. Issues identified for management actions included losses to predation, factors limiting bighorn sheep use of low elevation winter ranges, domestic sheep grazing, and unoccupied herd units. That plan also called for the development of regular demographic data on bighorn sheep herds and identified areas of desired research. Recovery goals to downlist to threatened calls for a minimum of 305 females distributed among the recovery units and the occupancy of 12 herd units; this condtions need to persist unaided for seven years for removal from the ESA.

To meet de-listing requirements, recovery activities focus on understanding and managing factors influencing population performance and expansion of the distribution of these sheep. Factors known or suspected to limit Sierra Nevada bighorn are risk of disease from domestic sheep, predation by mountain lions, forest succession, genetic diversity, severe weather, climate change, and reduced geographic distribution.

Currently the CDFW Sierra Nevada Bighorn Sheep Recovery Program is conducting winter and summer population surveys of all bighorn sheep herds, evaluating nutritional status, monitoring survival and habitat use patterns of more than 90 individuals, collecting data from more than 45 global positioning system (GPS) collars and identifying resource selection patterns across the Sierra Nevada. The program is also determining patterns of genetic variation across the sub-species, modeling risk of disease transmission from domestic sheep and goats, quantifying the effects of natural and prescribed fire on bighorn forage and habitat use, monitoring mountain lion movements, predation rates and population numbers, implementing and monitoring translocation efforts and modeling bighorn sheep response to various potential management actions. Information acquired during the various investigations is used to direct recovery activities.

Since their listing under the ESA, the Sierra Nevada bighorn sheep population has grown from about 125 individuals in 1999 to over 500 in 2012. Of the 16 herd units identified as suitable habitat for Sierra bighorn, 10 are currently occupied.