[9] Recent genetic testing indicates three distinct subspecies of Ovis canadensis, one of which is endangered: O. c. sierrae.

Wild sheep crossed the Bering land bridge from Siberia into Alaska during the Pleistocene (about 750,000 years ago); subsequently, they spread through western North America as far south as Baja California and northwestern mainland Mexico.

[16][17] This taxonomy is supported by the most extensive genetics (microsatellite and mitochondrial DNA) study to date (2016) which found high divergence between Rocky Mountain and Sierra Nevada bighorn sheep, and that these two subspecies both diverged from desert bighorn before or during the Illinoian glaciation (about 315–94 thousand years ago).

[18] Thus, the three subspecies of O. canadensis are: In addition, two populations are currently considered endangered by the United States government:[1] Bighorn sheep are named for the large, curved horns borne by the rams (males).

Males typically weigh 58–143 kg (128–315 lb), are 90–105 cm (35–41 in) tall at the shoulder, and 1.6–1.85 m (63–73 in) long from the nose to the tail.

[9] Male bighorn sheep have large horn cores, enlarged cornual and frontal sinuses, and internal bony septa.

Bighorn sheep inhabit alpine meadows, grassy mountain slopes, and foothill country near rugged, rocky cliffs and bluffs.

[8] Since bighorn sheep cannot move through deep snow, they prefer drier slopes, where the annual snowfall is less than about 150 cm (60 in) per year.

[22] Bighorn sheep are highly susceptible to certain diseases carried by domestic sheep, such as psoroptic scabies[23] and pneumonia; additional mortality occurs as a result of accidents involving rock falls or falling off cliffs (a hazard of living in steep, rugged terrain).

Predation primarily occurs with lambs, which are hunted by coyotes, bobcats, gray foxes, wolverines, jaguars, ocelots, lynxes, and golden eagles.

[20][25][26] Fire suppression techniques may limit visibility through shrublands, and therefore increase cover and predation rates by mountain lions.

[27] Bighorn sheep are considered good indicators of land health because the species is sensitive to many human-induced environmental problems.

Bighorn sheep graze on grasses and browse shrubs, particularly in fall and winter, and seek minerals at natural salt licks.

[29] Bighorn sheep exhibit agonistic behavior: two competitors walk away from each other and then turn to face each other before jumping and lunging into headbutts.

[34] Lambs born late may not have access to sufficient milk, as their mothers are lactating at a time when food quality is lower.

[38] Bighorn sheep were widespread throughout the western United States, Canada, and northern Mexico two hundred years ago.

[43][44] Unregulated hunting, habitat destruction, overgrazing of rangelands, and diseases contracted from domestic livestock all contributed to the decline, the most drastic occurring from about 1870 through 1950.

[45] Hunting for male bighorn sheep is allowed, but heavily regulated, in Canada and the United States.

The other sheep grant him power, wisdom, sharp eyes, sure-footedness, keen ears, great strength, and a strong heart.

The Bighorn sheep named Buford has a huge pair of horns in the Spring, Summer, Fall, and Winter, similar to Rudolph the Red-Nosed Reindeer.