Yellowstone National Park

Bighorn Sheep (Ovis canadensis)

Bighorn sheep (Ovis canadensis) once numbered in the millions in western United States and were an important food source for humans. The "Sheepeaters", related to the Shoshoni tribe, lived year-round in Yellowstone until 1880. Their principal food was bighorn sheep and they made their bows from sheep horns. By 1900, during an "epoch of relentless destruction by the skin hunters" (Seton 1913), bighorn numbers were reduced to a few hundred in the United States. In 1897 Seton spent several months roaming the upper ranges of Yellowstone Park and did not see any, although about 100-150 were estimated to be present. He reported that by 1912, despite a disease (scab) contracted from domestic sheep, bighorns in the park had increased to more than 200 and travelers could find them with fair certainty by devoting a few days to searching around Mt. Everts, Mt. Washburn or other well-known ranges. In winter, small bands of sheep could then be seen every day between Mammoth and Gardiner ..."4 great rams with about 40 other tame that one could get pictures within ten feet..."

Bighorn sheep are named for the large, curved horns borne by the males, or rams. Females, or ewes, also have horns, but they are short with only a slight curvature. Sheep range in color from light brown to grayish or dark, chocolate brown, with a white rump and lining on the back of all four legs. Rocky Mountain bighorn females weigh up to 200 pounds, and males occasionally exceed 300 pounds. During the mating season or "rut", occurring in November and December, the rams butt heads in apparent sparring for females. Rams’ horns can weigh more than 40 pounds, and frequently show broken or "broomed" tips from repeated clashes. Lambs, usually only one per mother, are born in May and June. They graze on grasses and browse shrubby plants, particularly in fall and winter, and seek minerals at natural salt licks. Bighorns are well adapted to climbing steep terrain where they seek cover from predators such as coyotes, eagles, and mountain lions. They are susceptible to disease such as lungworm, and sometimes fall off cliffs.

By 1914 there were about 210 sheep in Yellowstone and by 1922 there were 300 (Seton 1929). Censuses since the 1920s have never indicated more than 500 sheep. In recent years, bighorns have been systematically counted by aerial surveys in early spring. An annual ground count is also conducted on the winter range in the northern part of the park.

In the winter of 1981-82, an outbreak of pinkeye occurred among bighorns in the Mt. Everts area. Many sheep were blinded and/or killed on the adjacent park road or by falling from cliffs. No evidence of the disease, a natural occurrence, has been seen since. Winter visitors to the park still enjoy watching and photographing bighorns along the cliffs between Gardiner and Mammoth, as they did 80 years ago. Annual surveys of bighorn indicate that the resident herd on Yellowstone's northern range consists of at least 150-225 animals.

In 1997, a new study done by researchers at Montana State University began to investigate bighorn population status and behavior in northern Yellowstone. Of particular interest to these investigators is the effect of road use on the bighorns' ability to use their summer and winter range. Sheep are commonly seen along the road through the Gardner River Canyon, where visitors should be alert for bighorns crossing between their preferred cliffs and the river where they drink.

Summering bands are found in the Gallatin and Washburn Ranges, the Absarokas, and occasionally in the Red Mountains. On Dunraven Pass, a section of the Grand Loop Road in the park, a band of ewes and lambs has become somewhat habituated to summer traffic. These bighorns cause numerous traffic jams and are sometimes illegally fed by visitors, posing traffic hazards and danger to sheep. Park staff and visitors are encouraged to educate others about the importance of the "no feeding" regulation to the long-term welfare of wild animals.

* Information on this page provided by the NPS.

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