Bighorn Sheep

Bighorn Sheep climbs a snowy hillside
All bighorn sheep have horns. The rings on horns can be used to determine age, though it is easier to count the rings on a ram.

NPS / Jim Peaco


Although widely distributed across the Rocky Mountains, bighorn sheep (Ovis canadensis) persist chiefly in small, fragmented populations that are vulnerable to sudden declines as a result of disease, habitat loss, and disruption of their migratory routes roads and other human activities. About 10 to 13 interbreeding bands of bighorn sheep occupy steep terrain in the upper Yellowstone River drainage, including habitat that extends more than 20 miles north of the park. These sheep provide visitor enjoyment as well as revenue to local economies through tourism, guiding, and sport hunting. Mount Everts receives the most concentrated use by bighorn sheep year-round. Continue: Population and Competition with Other Species


Quick Facts

Number in Yellowstone

329 in the northern Yellowstone area in 2015 (163 counted inside the park).

Where to See

  • Summer: slopes of Mount Washburn, along Dunraven Pass.
  • Year-round: Gardner Canyon between Mammoth and the North Entrance.
  • Also: On cliffs along the Yellowstone River opposite Calcite Springs; above Soda Butte; in backcountry of eastern Absarokas.

Behavior and Size

  • Average life span: males, 9–12 years; females 10–14 years.
  • Adult male (ram): 174–319 pounds, including horns that can weigh 40 pounds. The horns of an adult ram can make up 8–12% of his total body weight.
  • Adult female (ewe): up to 130 pounds.
  • Horn growth is greatest during the summer and early in life. Female horns grow very little after 4–5 years, likely due to reproductive costs.
  • The horn size of bighorn sheep rams can influence dominance and rank, which affects social relationships within herds.
  • Older ram horns may be "broomed" or broken at the tip, which can take off 1–2 years of growth.
  • Mating season begins in November.
  • Ram skulls have two layers of bone above the brain that function as a shock absorber, an adaptation for the collision of head-on fighting that is used to establish dominance between rams of equal horn size, especially during mating.
  • One to two lambs born in May or June.


  • Feed primarily on grasses; forage on shrubby plants in fall and winter.
  • Rocky Mountain bighorn sheep, found in greater Yellowstone, differ from other currently recognized subspecies in the United States: Desert bighorn sheep, which is currently listed as an endangered species, Dall sheep found in Alaska and northwestern Canada, and Stone's sheep, which are a subspecies of Dall sheep.


  • Early reports of large numbers of bighorn sheep in Yellowstone have led to speculation they were more numerous before the park was established.
  • A chlamydia (pinkeye) epidemic in 1981–1982 reduced the northern herd by 60%.

More Information

Last updated: October 14, 2016

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