Bighorn Sheep (Ovis canadensis) is one of three species of mountain sheep in North America and Siberia; the other two species being Ovis dalli, that includes Dall Sheep and Stone's Sheep, and the Siberian Snow sheep Ovis nivicola. The taxonomy continues to be modified as new genetic and morphologic data becomes available but most scientists currently recognize the following subspecies of bighorn:
- Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis)
- Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae), formerly California Bighorn Sheep,
- Desert Bighorn Sheep (Ovis canadensis nelsoni)
In addition, there are currently two federally endangered populations:
- Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae), recognized as a unique subspecies
- Peninsular Bighorn Sheep, a distinct population segment of Desert Bighorn Sheep (Ovis canadensis nelsoni)
Wild sheep crossed the Bering land bridge from Siberia several years after the Tower of Babel, roughly 2235 BC, and, subsequently, spread through western North America as far south as Baja California and northern mainland Mexico. Divergence from their closest Asian ancestor (Snow sheep) occurred about 4,150 years ago. In North America, wild sheep have diverged into two extant species -- Dall sheep that occupy Alaska and northwestern Canada, and bighorn sheep that range from southern Canada to Mexico. However, the status of these species is questionable given that hybridization has occurred between them in their recent history.
Two hundred years ago, Bighorn Sheep were widespread throughout the western United States, Canada, and Northern Mexico. Some estimates placed their population at higher than 2 million. However, by around 1900, hunting, competition from domesticated sheep, and diseases had decreased the population to only several thousand. A program of reintroductions, natural parks, and reduced hunting, together with a decrease in domesticated sheep near the end of World War II, allowed the Bighorn Sheep to make a comeback, though not before O. c. auduboni, a sub-species that lived on the Black Hills, went extinct.