Bighorn Sheep

(Ovis canadensis)

Also known as mountain sheep, this heavy-bodied member of the cattle, goat, and sheep family has a remarkable ability to climb and jump. There are three types of wild sheep found in North America: (1) the grayish brown to pale buff Rocky Mountain sheep, (2) the white Dall sheep of Alaska and western Yukon, and (3) the dark-brown to black mountain sheep (also called 'stone sheep) that are found in south-central Yukon to central British Columbia.
 
In the past, disease, unlimited hunting, and overgrazing of livestock have pushed the bighorn sheep into a few mountain preserves. The numbers of bighorn sheep continues to shrink; only an estimated twenty-thousand survive in the United States today. Notable herds do still roam the mountain slopes of Yellowstone and Glacier national parks.
 
Another contributing factor to the numbers decline in bighorn sheep is inherent in their migration habits. Young bighorns follow in the footsteps of their parents, migrating year after year from the same summer feeding grounds in high mountain tundra to winter grazing grounds in the foothills. Young bighorns learn this migration route as they mature and do not vary from it. They do not disperse and colonize new areas as do other animals like white-tailed deer, moose, and bears. Therefore efforts to transplant bighorn sheep from one location to a different unpopulated are are often unsuccessful because the animals are unable to learn a new migration route.
Size: Male bighorn sheep, rams, typically grow to a length of about 5 to 6 feet from head to tail. They stand 2.5 to 3.5 feet tall at the shoulder. Adult males usually weigh from 175 to 275 pounds. Occasionally an old ram may exceed 300 lbs. Smaller female ewes grow to be 4 1/4 to 5 1/4 feet and seldom weigh over 150 lbs.
Characteristics: Bighorn sheep have excellent eyesight; it is almost impossible to approach a bighorn without being seen. The fur of bighorn sheep varies in color from dark brown to grayish brown in the northern mountains to a pale tan in desert locations. Their two-layer coat keeps it warm at high elevations. The outer layer consists of brittle guard hairs that overlay a thick, underfur, or fleece. This coat sheds in patches during June -July each summer. The bighorn sheep's underbelly, rump patch, back of their legs, muzzle, and eye patch are all a distinctive lighter white. Horns of both the ram and ewes are also a brown color. Bighorn sheep have a muscular body with a very thick neck and a short 5" dark brown tail They also have sturdy legs and sharp-edged black hooves.
Food: Bighorn sheep are primarily grass-eating animals, but also eat sedges and other herbs as they build up body fat in the summer months. In winter, when plants are dormant, they rely on browsing willows, shrubs, forbs, sage, bearberry, rose, and other woody plants. They get their water from mountain pools or by eating snow.
Gender: A male bighorn sheep is called a ram. A ram in its prime has massive, thick, ridged horns that curve backward, spiraling to encircle the ear. These horns continue to grow throughout their life. A 7 or 8 year old ram may have a full curl with tips even with their horn base. A few old rams even exceed a full curl, but often their horns become 'broomed.' A broomed horn is broken off near the tip or deliberately rubbed off on rocks so that the animal's peripheral vision is not impaired. These horns can weigh as much as thirty pounds on an aged bighorn, as heavy as all the bones in the sheep's body. You can count the age of a ram from their annual growth rings of its horns, just as you can with a mountain goat. Female ewe's (left photo) also have horns that are much shorter, slender, and only slightly curved, never forming more than a half curl. 
Habitat: All bighorn sheep migrate between high mountain slopes in the summer and foothill slopes in winter. They live in areas that are rarely disturbed by humans. Bighorns are found on high, rugged, sparsely wooded mountain slopes, cliffs, and rocky, lightly wooded canyons and foothills. They feed in early morning, at midday, and in the evening. Between grazing they lie down, resting, and chewing their cud and digesting their food. They return to a bedding spot each night, an area about 4 feet wide and wallowed down about 1 inch. This bed usually smells of their urine and is edged with droppings. Bighorn sheep return to these beds, staying for extended periods during their yearly migrations, and may use them again and again over several years.
 
Herding: Bighorn sheep are gregarious animals. In spring, rams band together in groups of 3 to 5 and move to higher summer ranges to roam during the summer. Ewes likewise band together with their lambs and yearlings into groups of 5 to 15 and move to separate high areas. In fall, the rams separate from each other to each join bands of ewes and young during the rutting season. Bighorn sheep of all ages and sexes band together in herds of hundreds for the winter months. They are then led by an elder ewe who moves them around lower valley elevations.
Locomotion: The halves of each hoof separate, so that a bighorn sheep's' feet cling firmly to steep and rocky terrain. The hooves are hard at the outer edge and spongy in the center. The soft, rubbery and cushion-like padded soles permit them to keep their balance and add traction as they move across uneven and slippery ground and even scale up sheer rock faces. Their hoof prints, similar to deer's, are 3 to 3.5" long with hind prints slightly smaller than fore prints. Unlike deer prints, bighorn prints are less pointed, less heart-shaped, more splayed, and have straighter edges.  If walking downhill on soft ground, their dew claws may print two dots behind their hoof print.
 
Bighorn sheep follow narrow trails over mountainsides and steep slopes. In addition to being excellent climbers and jumpers, bighorn are also good swimmers. A bighorn's walking stride is about 18 inches, the bounding gait on level ground is around 15 feet, and down a steep incline it increases to near 30 feet.
Reproduction: Breeding season generally occurs between October and December (At different latitudes, season can begin as early as August and extend to early January). As the fall rutting season approaches, rams have head-butting contests that increase in frequency as the season progresses. Horn size determines status; fights occur only between rams with similar size horns. Two opponents rear back onto their hind legs, then drop to all fours and charge each other at speeds greater than 20 mph. Their foreheads slam together with a crack that can be heard for more than a mile. The shock wave reverberates through their bodies. They pause a minute to regain their footing and posture themselves. Again and again, protagonists put their full weight behind their charges and clashes with each other. The sound often prompts other rams in the area to similar contests. Battles between rivals can last up to 20 hours. Chips of horn may fly and blood may ooze from ear and nose, but finally one of the battlers, exhausted or injured, lowers its head in submission and the winner strides away to claim the ewe. Both victor and vanquished earn the nose scars and blunted horns of a veteran bighorn battler. With nose elevated and their upper lip curled, rutting males follow any female in heat. They occasionally stop for butting jousts if other males begin to follow the same ewe. Ewes usually breed at 2 1/2 years of age, but may breed earlier as yearlings.
In spring after the annual migration back to the high country and after a 180 day gestation period, expectant ewes slip away to a sheltered ledge and give birth to a single well-developed lamb. Newborn lambs have a soft, woolly, light-colored coat and small horn buds. The newborn remains hidden for about one week, then follows its mother about, quickly learning to feed on tender grasses, and is weaned after 5 to 6 months (Photo at right is of ewe and lamb, latter was born the previous year).
Range: Bighorn sheep are found in the mountain ranges of southern California, Arizona, and New Mexico northward through Idaho and Montana and on into British Columbia.
 
Predators: Predators of Bighorn sheep include cougars, golden eagles, wolves, coyotes, bears, bobcats, and lynx. On cliffs, adult Bighorns can easily escape all but the cougars. When they migrate--descend to the foothills, the bighorn's sure-footedness is no advantage and they may then fall prey to predators. Golden eagles attack young lambs whenever they find them unprotected.
 
More Information

For more information about bighorn sheep, visit these sites.

Bighorn Mountain Sheep (British Columbia Adventure Network)
Here you can find information on the description, tracks, habitat, and behavior of bighorn sheep.
Rocky Mountain Bighorn
This student project webpage provides pictures, information, and a drawing of the Rocky Mountain Bighorn Sheep.
Sierra Nevada Bighorn Sheep by Robin Meadows
A May/June 1999 article in Zoogoer magazine outlines the plight of a dwindling bighorn sheep population in Califorinia's Sierra Nevada Mountains.
Bighorn Sheep (Teachers' Corner)
Site developed for teachers contains links to other bighorn sheep websites.

Try a webquest activity.

Note: All photographs were taken with a digital camera in Rocky Mountain National Park (Colorado), Hells Canyon (Idaho), and Yellowstone National Park (Wyoming) during July and August, 1999. Pictures also came from Glacier National Park (Montana/Canada) 2001.

Developed by Annette Lamb and Larry Johnson, 6/99. Update 4/02.