Bighorn Sheep (Ovis canadensis) Fact Sheet: Population & Conservation Status

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)

IUCN Status

• Least Concern (2019 assessment) (Festa-Bianchet 2020)
  • Overall species trend: stable
• Previous assessments
  • 2008: Least Concern
  • 1996: Lower Risk/conservation dependent

CITES

• 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
  • O. c. nelsoni (Peninsular bighorn sheep) and O. c. ssp. sierrae (Sierra Nevada bighorn sheep)
• Ovis canadensis is not listed at the species level

Hunting

• 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.

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)
USFWS (2000)
Shackleton (1997)
Rubin (1998)