Common Name: Bighorn Sheep
Species: Ovis canadensis
photo M. Noonan
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
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.
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.
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.
"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
donít 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
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.
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!
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.
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
Artiodactyla Ė 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
ruminant - any hoofed animal that
digests its food in two steps, first by ingesting the
raw material, such as grass or leaves, then
regurgitating it in partially digested form, called the
cud, which is then also eaten