Bighorn Sheep (Ovis canadensis): Facts, Horns and Habitat

What does a bighorn sheep look like?

Bighorn sheep are stocky, muscular wild sheep with a coat that ranges from light brown to grayish or dark chocolate brown. They have a large white rump patch, a short dark tail and white lining on the backs of all four legs. The muzzle is pale. The summer coat is glossy brown and fades by late winter. Despite being sheep, they have no woolly fleece like domestic sheep: their coat is made of brittle outer guard hairs over a short, crimped gray underfur.

The horns are the signature feature. Rams (males) grow massive, ridged horns that sweep back and curl down and forward around the ears, reaching a full curl in older rams. Ewes (females) also grow horns, but theirs are short, slender and only slightly curved. Desert bighorns tend to be smaller and paler than mountain bighorns and their rams often have horns that flare outward more widely.

How big is a bighorn sheep?

Rams are much larger than ewes. Adult rams usually weigh 58–143 kg (128–315 lb) and ewes 34–91 kg (75–200 lb). Rams stand about 90–105 cm (35–41 in) at the shoulder and measure 1.6–1.85 m (5.2–6.1 ft) from nose to tail, while ewes stand 75–90 cm (30–35 in) tall.

Size varies by region. Rocky Mountain bighorns in Canada and the northern US are the largest, and exceptional rams there have been reported at well over 140 kg. Sierra Nevada bighorns are smaller, with rams up to about 90 kg (198 lb), and desert bighorns are also lighter than their northern relatives.

A ram’s horns alone can weigh up to about 14 kg (30 lb), roughly as much as the rest of his skeleton. See How much do bighorn sheep horns weigh?

Subspecies: mountain and desert bighorns

Wild sheep reached North America from Siberia across the Bering land bridge during the Ice Ages. Their descendants split into two species: the thin-horned Dall sheep of Alaska and northwestern Canada, and the bighorn sheep further south.

Older classifications named seven bighorn subspecies, but genetic studies since the 1990s support three:

• Rocky Mountain bighorn (O. c. canadensis), in the Rocky Mountains and other ranges of Canada and the northwestern and central US.
• Sierra Nevada bighorn (O. c. sierrae), found only in the Sierra Nevada of California.
• Desert bighorn (O. c. nelsoni), in the desert mountains of the southwestern US and northwestern Mexico, including the Peninsular Ranges and Baja California.

The Badlands or Audubon’s bighorn of the northern Great Plains, once treated as a separate subspecies, was wiped out in the early 1900s.

Where do bighorn sheep live?

Bighorn sheep live from southern British Columbia and Alberta south through the Rocky Mountains, the Great Basin and the Sierra Nevada to the deserts of Nevada, California, Arizona, New Mexico and west Texas, and into Baja California and Sonora in Mexico. Their range today is patchy, made up of many separate herds, and much of it has been restocked by moving sheep from healthy herds.

The key to bighorn habitat is “escape terrain”: steep, rocky cliffs and outcrops close to open grassy slopes where they can feed. Mountain bighorns use alpine meadows in summer and move down to lower, drier slopes in winter, because they cannot paw through deep snow. Desert bighorns live in rugged, rocky desert ranges and get much of their water from plants, though they still visit springs and water holes every few days in hot weather.

How do bighorn sheep climb so well?

Bighorn sheep are superb climbers. Each hoof has a hard outer rim and a softer, slightly spongy inner pad that grips rock like the sole of a climbing shoe, and the two toes can spread to fit uneven ledges. They can stand on ledges only about 5 cm (2 in) wide and bound from ledge to ledge across gaps of up to about 6 m (20 ft).

They also have sharp eyesight that helps them judge distances when jumping and spot predators far away; they often watch animals moving well over a kilometer off. On level ground, bighorns can run at about 48 km/h (30 mph), and they scramble uphill at around 24 km/h (15 mph). Cliffs are their main defense: a sheep that reaches steep rock is usually safe from most predators.

What do bighorn sheep eat?

Bighorn sheep are herbivores. Mountain bighorns are mainly grazers that eat grasses, sedges and forbs (small flowering plants), switching to more shrubs and woody browse in fall and winter when grass is scarce or buried. Desert bighorns eat a wide range of desert plants, including shrubs, grasses and cacti.

Like cattle and domestic sheep, they are ruminants: they swallow food quickly, then rest and chew the cud later, often while lying on a ledge where they can watch for danger. Bighorns also visit natural mineral licks to get salt and other minerals.

Behavior and the rut

Bighorn sheep live in herds. For most of the year, ewes, lambs and young sheep form groups led by older ewes, while mature rams live separately in bachelor groups. Herds of 8–10 are typical, though more than 100 can gather in good winter ranges. Young sheep learn migration routes and good feeding areas by following older animals.

The rut, or mating season, peaks in November and December in northern herds; in desert populations it can run from about July to December. Before and during the rut, rams sort out who is dominant. Horn size, body size and age all count, and rams display their horns, kick and shove each other. When two rams are closely matched, they rear up, run at each other and crash horns, a clash that can be heard far across a valley. Contests can last hours, and one was recorded as lasting more than a day. See Why do bighorn sheep butt heads?

Dominant rams follow and guard ewes in season, and most rams do not get to mate until they are about seven years old.

Reproduction and lifespan

Ewes are pregnant for about six months, so most lambs are born from late April to June. A ewe usually has a single lamb, rarely twins, which weighs about 3.6–4.5 kg (8–10 lb) at birth. Before giving birth, ewes move to steep, secluded cliffs where predators struggle to reach them. Lambs can walk within hours and follow their mothers across rough ground within days. They are weaned at about 4–6 months.

Ewes usually live 10–14 years and rams 9–12 years in the wild, as rams wear themselves out in the rut. A few females have reached about 19 years.

Predators and threats

Adult bighorns are hunted mainly by cougars (mountain lions), which can stalk them in rocky country, as well as by gray wolves, bears and coyotes. Lambs are also taken by golden eagles, bobcats, lynx and coyotes. Rockfalls and falls from cliffs kill some sheep, and harsh winters can cause heavy losses.

The most serious threat today is disease. Domestic sheep and goats can carry bacteria, especially Mycoplasma ovipneumoniae, that cause pneumonia in bighorns. When these pathogens reach a wild herd, die-offs can kill up to 90 percent of the animals, and lambs may keep dying for years afterwards. Wildlife managers therefore try to keep wild and domestic sheep apart. Habitat loss, fragmentation and roads also isolate herds.

Conservation status

Bighorn sheep once numbered in the hundreds of thousands, with some estimates far higher. Unregulated hunting, overgrazing by livestock and diseases from domestic sheep caused a steep decline from the late 1800s through the mid-1900s, and by the early 1900s only a few thousand to a few tens of thousands survived.

Protection and decades of reintroductions have brought bighorns back to many ranges, and the species is now listed as Least Concern by the IUCN. Even so, it occupies only part of its historic range, and many herds are small and vulnerable to disease. Two US populations are listed as endangered: the Sierra Nevada bighorn, which fell to around 100 animals in the mid-1990s, and the Peninsular bighorn of the mountains of southern California.

Bighorn sheep and people

Bighorn sheep have long been important to Native American peoples, who used their meat and hides and made bows and tools from their horns. The Bighorn Mountains and Bighorn River in Wyoming and Montana are named after them. The Rocky Mountain bighorn is the state animal of Colorado and the provincial mammal of Alberta, and the desert bighorn is the state mammal of Nevada.

Today bighorn sheep draw wildlife watchers to parks such as Yellowstone (see animals of Yellowstone), Glacier, Banff and Joshua Tree. Sheep near roads can seem tame, but they are wild animals: visitors should keep their distance, never feed them and drive slowly where sheep come down to lick road salt.