Bighorn Taxonomy/Description

Bighorn sheep belong to the Mammalian Order Artiodactyla, in the family Bovidae. Bovidae also includes goats, bison, cattle, and antelope. The bighorn's scientific name is Ovis canadensis, which means "sheep belonging to Canada". However, the bighorn sheep's range is not limited to only Canada.

photo M. Noonan

One of the most important features of the bighorn sheep is the unique structure of its hooves. Rather than being hard like those of a horse or cow, the sheep have rubber-like hooves that allow excellent mobility on steep rock faces. The males, called rams, have massive spiral horns that can weigh up to 40 lbs. A ram itself can weigh as much as 400 Lbs. Females (or ewes) have short, spike-like horns and weigh about 150 lbs. The pelage (its coat) is typically chocolate brown with white areas on the rump and on the underside. These amazing animals live as long as 15-20 years in the wild, and even longer in captivity.

photo M. Noonan

Bighorn Habitat/Diet

Different subspecies of the bighorn sheep can be found throughout the mountainous areas of the western United States. We studied the Rocky Mountain bighorn sheep in both South Dakota and Colorado. Their habitat can range from desert cliffs through arid mountain ranges to alpine tundra. The animals usually stay within a limited home range which gives them access to food, water and rest areas. A critical element of Bighorn habitat is the requirement for escape terrain. Sheep always stay close to an area that will allow them to climb up or down a steep hillside quickly if danger is present.

photo M. Noonan

Bighorn sheep live mostly on grasses, but they will also eat many other plant species when they are available. After feeding in the morning, sheep characteristically take a mid-day nap to rest and digest their food. Sheep are ruminants, which means that they have a four chambered stomach. Bacteria in these compartments aid in digestion of plant material and provide nutrients that sheep need to live.

photo M. Noonan

Bighorn Behavior/Reproduction

"Brooming" is a behavior in which males break off the tips of their horns by wedging them in rocks or trees. It is suspected they do this to prevent their horns from blocking their vision. Subordinate males will perform "horning" where they will rub their heads on the scent glands on the dominant male's head. It is suspected that this allows the lower ranked males to pick up the scent of the higher ranked ones. Males are sexually mature by their fourth year but don’t usually manage to breed until their seventh or eighth year because the older rams are much bigger and stronger. Females breed for first time in their third year.

photo M. Noonan

Breeding season is from November to January with its peak in December. During this time, males fight by head butting with their massive horns. Fighting is not the only way to secure a mate however. Sometimes a third ram comes in and mates with the female while the first two are occupied in a fight. The gestation period is 174 days. Lambing peaks in June. Ewes ordinarily give birth to only one lamb at a time. The young are precocial at birth.

photo M. Noonan

Our Experiences with Bighorn

While in South Dakota, we were privileged to study with wildlife biologist Michelle Bourassa. She allowed us to accompany her in Badlands National Park while she tracked radio-collared bighorn sheep that were part of re-introduction program there. After using radio telemetry to triangulate on their position, we spent hours hiking across the rugged terrain in search of the sheep. At long last, Michelle spotted a mature ram off in the distance resting on a cliff. We were able to view the sheep with a powerful spotting scope. The ram, with its incredible eyesight, was looking directly at us from over a mile away. We were amazed that the sheep could see us at that great distance. We were even more amazed that Michelle Bourassa had seen the sheep!

photo M. Noonan

Colorado yielded an entirely new experience with bighorn sheep. While exploring very rocky terrain in the backcountry, a group of females began making their way down the mountain directly in front of us. To avoid disturbing them, we slowly backed away to let them travel down their preferred path and they elected to pass right in front of us! It was a very special moment for all of us.

photo M. Noonan

Bighorn Conservation

Bighorn sheep have not had an easy time adapting to human activity. Unfortunately, until recently they have suffered a steady decline in population. Human encroachment on bighorn habitat is the main cause of the species' decline. The more land that humans occupy, the less there is for wildlife to utilize. In addition, the Bighorn sheep has been a favorite trophy for hunters since settlers first came to this land. The numbers of sheep were diminished so greatly that some entire portions of their original range have been cleared of wild sheep. Another killer of wild sheep is disease. Some diseases are transmitted to bighorn by domestic sheep that are ranched in the same habitat that the wild sheep occupy. Bighorn sheep populations are now finally on the rebound due to the hard work of individuals dedicated to preserving and studying them. Re-introduction of bighorn sheep in places like Badlands National Park has begun to restore populations and may assure the survival of this remarkable animal.

photo M. Noonan

Glossary:

Artiodactyla – Mammalian Order meaning "even toed", which consists of all even-toed hoofed mammals, including families that contain cattle, antelope, deer, camels, and hippopotamuses

precocial - relatively mature and mobile from the moment of birth