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Bighorn
Sheep
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(Ovis
canadensis)
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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.
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- 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.
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- 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.
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| 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. |
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| 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. |
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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. |
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- 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.
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- 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.
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- 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.
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- 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.
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| 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. |
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| 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). |
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- 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.
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- 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.
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- 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)
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Site
developed for teachers contains links to other bighorn sheep websites.
Try a
webquest activity.
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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.
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