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More recent population estimates (Festa-Bianchet 2008; Wilson and Mittermeier 2015)
- Canada: about 15,600 individuals
- United States: about 42,700 individuals
- Only rough population estimates available for Mexico
- About 6,700 individuals
- 2,500 in Baja California
- 4,200 in Sonora (half free-ranging, half in enclosures)
Previous population estimates
- Bighorn sheep subspecies in North America were estimated at 1.5-2 million during pre-Columbian periods (Seton 1929)
- By 1960, the population of bighorn sheep in North America dropped to 15,000-18,200 (Buchner 1960)
- Major declines occurred from 1850's to early 1900's due to hunting (Buchner 1960)
- In 1960, the total desert bighorn sheep population was estimated at 7,065-8,475
- In 1993, the overall desert bighorn sheep population increased to 18,965-19,040
- The California desert bighorn sheep subspecies were estimated in 1960 at 2,150-2,450, 1993 at 4,300-4,325
- The endangered Peninsular bighorn sheep, a population of desert bighorn sheep was estimated in 1993 at 400-425 in California, and 780-1,170 in Baja California, Mexico
- March 18, 1998: United States Peninsular Ranges population of desert bighorn sheep was federally listed United States Fish and Wildlife Service as an endangered species
- Census from Shackleton, 1997: O. c. cremnobates <2,500, O. c. mexicana >2,000?, O. c. nelsoni 15,000? O. c. weemsi 500?
(Low Risk northern species: O. c. californiana 8,900; O. c. canadensis 36,700)
- Least Concern (2019 assessment) (Festa-Bianchet 2020)
- Overall species trend: stable
- Previous assessments
- 2008: Least Concern
- 1996: Lower Risk/conservation dependent
- Appendix II: only the population of Mexico included
- Other populations not included
- No other population is included in the CITES Appendicies
Endangered Species Act (US Fish & Wildlife Service)
- Endangered status for two subpsecies
- Ovis canadensis is not listed at the species level
Threats to Survival
- Populations of Sonora and Baja (cremnobates, nelsoni, mexicana, and weemsi) have been greatly reduced due to widespread illegal hunting of trophy males.
- Illegal take of trophy males within national parks (Festa-Bianchet 2008)
Habitat and ecological issues
- Human disturbance (Bighorn sheep are not able to live near areas of human activity.)
- Habitat loss, degradation, and fragmentation by urban and commercial development
- Failure of populations to disperse into contiguous, suitable habitat
- Fire suppression has created taller, denser vegetation. Reduced visibility makes the bighorn more vulnerable.
- Drought limiting water & forage. Global warming may be a problem for the desert bighorns in some areas.
Competitors and predators
- Competition from domestic sheep, goats, feral burros for forage, water, space
- Invasive plant species (e.g., tamarisk) compete with native plants bighorns feed on.
- Introduced Barbary sheep could take over bighorn habitat.
- Mountain lion, wolf predation coinciding with low population numbers
Disease and life history challenges
- Unpredictable epizootics (rapidly spreading disease affecting a large number of animals throughout a wide range)
- Pneumonia and mange; observed particularly in populations with contact to domestic sheep (Festa-Bianchet 2008)
- Populations have a predominance of old indiviuals and insufficient lamb recruitment (relationship between production and survival)
- Loss of genetic variation is always a danger when dealing with small populations.
- U.S. began preserving large parcels of wildlands as early as 1872 with the establishment of Yellowstone. Animals in National Parks are protected
- A genetic ID program has been initiated in Jaspar National Park to deter trophy poaching.
- Management consists of establishing hunting quotas, regulating harvests, habitat improvement, annual censuses, translocation of animals and promoting research
- State wildlife agencies have reintroduced bighorns into many native ranges as well as into areas where the animals did not naturally occur
- Many non-governmental conservation organizations are involved in protecting bighorns. San Diego Zoo Wildlife Alliance has had a Conservation Program for the Peninsular Bighorn since 2000.
The Next Generation
Bighorn sheep populations in the United States and Canada are doing well.
Populations in Mexico are more at risk.
Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.
IUCN website (2002)
SDZWA Library Links
Fact Sheet Index
Fact sheet index, San Diego Zoo Wildlife Alliance Library
Home page, San Diego Zoo Wildlife Alliance Library
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