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.
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