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Big Horn Sheep
Names and Geographic Range
Ovis canadensis is found in the Rocky Mountains from southern Canada to Colorado
Ovis canadensis nelsoniis found from Nevada and California to west Texas and south into Mexico.
Physical Characteristics
Mass: 53-91 in females, 119-127 kg in males.
Rams typically measure 160-180 cm from head to tail.
Ewes are approximately 150 cm.
Bighorn sheep are very alert and have remarkable eyesight allowing them
to judge distances accurately in jumping and locate footholds. Their
eyesite has been noted and often watch other animals moving at
distances of up to a mile away.
Bighorn sheep have double-layered skulls for their protection in a
battle. They also have a broad, massive tendon linking skull and spine
to help the head pivot and recoil during blows. The horns may weigh as
much as 14 kg, which is the total weight of all the bones in a ram's
body. The horns of a female are much smaller and only slightly curved.
The horns tell the story of a ram's life, such as his age, health, and
fighting history. Ovis canadensis nelsoni, is somewhat smaller and has
flatter, wider-spreading horns. The coat of Ovis canadensis is smooth.
The outer coat has brittle guard hairs and a short, grey, crimped
fleece underfur.
Facts
The bighorn eats various grasses, plants, and
leaves. Like all sheep it digests its food in a four-chambered stomach
which allows it to eat tough plants. The bighorn mainly eats in the
mornings and evenings, wandering around as it feeds. After grazing it
chews cud while resting in a location that has a good view of the area.
Desert bighorns eat a variety of desert plants and get most of their
moisture from the vegetation, they visit water holes every several days.
Reproduction
Known as the Rut, this happens in the autumn
and early winter, and births take place in the spring. Mating for the
desert bighorn, can last from July to December. Gestation lasts from
150-180 days, and litters contain between 1 and 4 young. Newborns are
able to follow their mothers at a good pace over the rocky terrain
after the first week. Within a few weeks of birth, offspring form bands
of their own, seeking out their mothers only to suckle occasionally.
They are completeley weaned by 4-6 months of age. Ovis canadensis
females generally do not breed until their second or third year, but in
captivity they have mated at 10 - 12 months old. Ewes are seasonally
polyoestrous and will accept several rams, and frequently, when in
oestrus. Because of intense competition between males for females and
the dominance hierarchy based on age and horns, males do not usually
mate until they are seven years old unless the dominant rams of their
group are killed. Steep slopes and canyons in the Protected Area
provide valuable escape terrain; sheep can escape down steep slopes and
into treed canyons with great speed and agility. Lambing areas are
usually rugged and remote in order to provide ewes with security and
isolation from predators. Lambing occurs between mid April and early
July, with the peak occurring from mid May to mid June.
Most sheep live over 10 years, with a maximum of 20 years. But with an
expanding population with heavy reproduction, the average life span now
is only 6-7 years.
Behavior
Bighorn sheep are probably best known for the head-to-head combat
between the males. The horn size is a symbol of rank, and the mass of
the horns, weigh as much as 14 kg, is used to a male's best advantage
during the rut, as he smashes into an opponent at speeds up to 20 miles
per hour. Combat has been observed to last for as long as 25 hours or
until one of the males leaves. Males do not defend territories but will
only engage in a battle during mating season for a particular female.
The male status is determined by age as well as horn size. Bighorn
sheep have be seen zigzagging up and down cliff faces using ledges only
2 inches wide for footholds, and they look as though they bounce from
ledge to ledge over spans as wide as 20 feet. They can move over level
ground at speeds of 30 miles per hour and scramble up mountain slopes
at 15 mph. Surprisingly they also swim, even with their heavy coat and
the weight of their horns.
Bighorn sheep can gather in herds of over 100 individuals, but usually
smaller groups of 8-10 are more common. Mature males usually stay in
separate bachelor flocks. Young females generally remain in their
mother's group which is led by an old ewe, but males will leave when
they are two to four years old and will join a group of rams. The young
learn migratory paths and suitable feeding grounds from older adults in
the group.
Habitat
Big Horn inhabits alpine meadows, grassy mountain slopes and foothill
country in proximity to rugged, rocky cliffs and bluffs. They stay
close to rocky cliffs, and is important to their survival, if attacked,
if sheep can reach a rocky outcrop or cliff, it is usually safe.
Preditors of the sheep are wolves, coyotes, bears, bobcats and lynx.
In the fall the rams join the ewes, or females, to form herds of up to
100 and move to the lower valleys. Bighorn sheep also require drier
slopes where the annual snowfall is less than sixty inches a year,
since they paw through deep snow to feed.
Once it turns spring, they split up and move back to the high slopes again. The summer range is between 6,000-8,500 feet
There is special concern with the conservation of the Big Horn and are
threatened with eventual extinction, bighorn numbers are only one-tenth
the population that existed when white people first began exploring the
Rockies. Their main enemies are poachers and diseases introduced by
domestic sheep, competing with livestock, and human invasion on their
habitat. The subspecies Ovis canadensis auduboni of the Black Hills and adjacent areas has already become extinct.
California bighorns are blue-listed in B.C. California bighorn sheep are
threatened by past overgrazing, and illegal poaching still occurs.
Trophy hunters are particularly damaging to the strength of bighorn
herd because this eliminates the strongest, breeding males. Recovery
has been slow for these animals and their future is uncertain unless
further conservation measures are taken.
More Information
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