Related Species
The Desert Bighorn are
comprised by some accounts of four subspecies. They
live in dry, desert mountain ranges and foothills,
near rocky cliffs, in an environment that is almost
waterless and relatively barren of vegetation. In the
winter they range farther from their meager water
sources to browse on vegetation in full leaf. As
summer approaches, they move closer to remaining water
supplies and reduce their own water output by resting
during the day in caves or under rocky overhangs.
Comparisons
One of the six species
of the genus Ovis, Dall Sheep (O.
dalli), are often seen high on mountains of
northwestern Canada and Alaska. Dall Sheep are smaller
than Bighorn, weighing only about 150 pounds maximum,
and vary in color from white to almost black.
Description
The Bighorn's body is
compact and muscular; the muzzle, narrow and pointed;
the ears, short and pointed; the tail, very short. The
fur is deerlike and usually a shade of brown with
whitish rump
patches. The fur is smooth and composed of an outer
coat of brittle guard hairs and short, gray, crimped
fleece underfur. The summer coat is a rich, glossy
brown but it becomes quite faded by late winter.
The male sheep is called
a ram and can be recognized by his massive brown
horns. The horns curl back over the ears, down, and up
past the cheeks. By the time a ram reaches 7 or 8
years of age, he can have a set of horns with a full
curl and a spread of up to 33 inches. Ewes, the
females, are smaller than the rams and have shorter,
smaller horns that never exceed half a curl.
The desert subspecies,
Ovis canadensis nelsoni, is somewhat smaller
and has flatter, wider-spreading horns.
Vocalization
During the rut, the Bighorn rams will snort
loudly. The lambs bleat, and the ewes respond with a
guttural "ba." They also utter throaty rumbles or
"blow" in fright.
Eyes
Bighorn have extremely acute eyesight, which aids in
jumping and gaining narrow mountain footholds. They
often watch other
animals
moving at distances of up to a mile away.
Tail
The Bighorn's tail is very short.
Ears
The ears are short and pointed.
Nose
The Bighorn's muzzle is narrow and pointed.
Feet
The cloven hooves are sharp-edged, elastic, and
concave. They are double-lobed, 3-3.5 inches long with
foreprints slightly larger than hindprints -- similar
to deer prints but less splayed.
Behavior
Bighorn sheep are
gregarious, sometimes forming herds of over 100
individuals, but small groups of 8-10 are more common.
Mature males usually stay apart from females and young
for most of the year in separate bachelor herds. They
migrate seasonally, using larger upland areas in the
summer and concentrating in sheltered valleys during
the winter.
Males do not defend
territories but rather engage in battles over mating
access to a particular female. Age as well as horn
size determines male dominance status. Although not as
well built for climbing as mountain goats, Bighorn
Sheep zigzag up and down cliff faces with amazing
ease. They use ledges only 2 inches wide for
footholds, and bounce from ledge to ledge over spans
as wide as 20 feet. They can move over level ground at
30 miles per hour and scramble up mountain slopes at
15 m.p.h. They also swim freely, despite their massive
bulk and the weight of their horns.
Bighorns are generally
active during the day, feeding morning, noon and
evening, then lying down to chew their cud. They
retire to their bedding areas for the night, which may
be used for many years.
Desert Bighorns utilize
two mechanisms for cooling -- perspiring, and also
panting, which is a fairly uncommon adaptation for
desert animals. When the summer rains finally arrive,
they resume the more common behavior of their species.
Habitat
Bighorn inhabit alpine meadows, grassy mountain
slopes and foothill country near rugged, rocky cliffs
and bluffs, allowing for quick escape. In winter,
Bighorn prefer slopes 2,500-5,000 feet where annual
snowfall is less than 60 inches a year, because they
cannot paw through deep snow to feed. Their summer
range is between 6,000-8,500 feet in elevation.
Food
Bighorn are primarily grazers, consuming grasses,
sedges, and forbs, but will eat young twigs, leaves,
and shoots when preferred food is scarce (especially
in winter). Desert bighorns (O. c. nelsoni) eat
a variety of desert plants and get most of their
moisture from the vegetation, although they still
visit water holes every several days in summer.
When summer temperatures
become extreme and water sources dry up completely,
Desert Bighorns rest most of the daylight hours and
feed at night. During this season, they rely on
certain desert plants for both food and moisture. They
use their hooves and horns to remove spines from
cacti, then eat the juicy insides. They are fond of
the tender shoots of Prickly Pear and Cholla, and the
flowers of succulents like Agave and Squawgrass.
Breeding
Rutting season is in the autumn and early winter,
and births take place in the spring though mating can
last from July to December. Gestation lasts from
150-180 days. One or two lambs are born from late
February to May. Within a few weeks of birth, lambs
form bands of their own, seeking out their mothers
only to suckle occasionally. They are completely
weaned by 4-6 months of age.
In the desert, only
about one-third of the lambs will survive their first
summer. A lamb born late in the season stands little
chance of survival, since temperatures reach over 100
degrees F in May and often reach 120 F by June. Recent
studies of high lamb death rates focus on viruses
possibly introduced by domestic livestock, to which
the native Bighorn have little or no immunity.
Female Bighorn usually
do not breed until their second or third year in the
wild. Due to competition, males do not usually mate
until they are 7 years old. Most sheep live over 10
years, with a maximum of 20 years.
Ewes are protective of
their young for many months. Yearlings, often
abandoned while the ewe is giving birth to her next
lamb, may be seen again with the ewe and lamb late in
the spring. Bighorn find safety in numbers and are
ever watchful for predators such as
Coyotes
and Mountain Lions.
Conservation
Threatened with eventual
extinction, Bighorn numbers are only one-tenth the
population that existed when Europeans first began
exploiting the Rockies. The subspecies Ovis
canadensis auduboni of the Black Hills and
adjacent areas has already become extinct. Hunting has
been prohibited or controlled since the early 1900s,
but much illegal poaching still occurs.
In March, 1998, the
Peninsular Bighorn Sheep was listed as endangered by
the U.S. Fish and Wildlife Service. Today, Bighorn
still range into Baja California, but their numbers
have dwindled to less than three percent of the
estimated 1.5 million of the early 1800s. In 1979
Bighorn between Mt. San Jacinto and the Mexican border
were estimated to number 1,180; in 1996 that number
had plummeted to 280 sheep.
Recent genetic evidence
indicates the Sierra Nevada Bighorn is a unique form
of Bighorn found only in the Sierra Nevada. Sierra
Nevada Bighorn are rarer than the Florida Panther, and
rarer than the California Condor. They are clearly one
of the most endangered mammals of North America. In
1986 these sheep were reintroduced to the Mono Basin
from a population further to the south. Now the
population in Lee Vining Canyon is the primary hope
for the future of Sierra Nevada Bighorn.
Cautions
Human activities are responsible for the Bighorn's
decline. Grazing, mining, depletion of water holes,
homesteading and use as camp meat spelled disaster for
the Bighorn. In the desert, off-road vehicles,
trespassing cattle, poaching in the 1960s and early
'70s,
drought,
disease and Mountain Lion predation have worked
together to push this population to the edge of
extinction.
