Bighorn Sheep

The **bighorn sheep** (*Ovis canadensis*) is a species of sheep native to North America named for its large horns. These horns can weigh up to 30 lb (14 kg), while the sheep themselves weigh up to 300 lb (140 kg). Recent genetic testing indicates three distinct subspecies of *Ovis canadensis*, one of which is endangered: *O. c. sierrae*. Sheep originally crossed to North America over the Bering land bridge from Siberia: the population in North America peaked in the millions, and the bighorn sheep entered into the mythology of Native Americans. By 1900, the population had crashed to several thousand, due to diseases introduced through European livestock and overhunting.

## Description

Bighorn sheep are named for the large, curved horns borne by the rams (males). Ewes (females) also have horns, but they are shorter with less curvature. They range in color from light brown to grayish or dark, chocolate brown, with a white rump and lining on the backs of all four legs. Males typically weigh 127–316 lb (58–143 kg), are 36–41 in (91–104 cm) tall at the shoulder, and 69–79 in (180–200 cm) long from the nose to the tail. Females are typically 75–188 lb (34–85 kg), 30–36 in (76–91 cm) tall and 54–67 in (140–170 cm) long. Male bighorn sheep have large horn cores, enlarged cornual and frontal sinuses, and internal bony septa. These adaptations serve to protect the brain by absorbing the impact of clashes. Bighorn sheep have preorbital glands on the anterior corner of each eye, inguinal glands in the groin, and pedal glands on each foot. Secretions from these glands may support dominance behaviors.

Bighorns from the Rocky Mountains are relatively large, with males that occasionally exceed 500 lb (230 kg) and females that exceed 200 lb (90 kg). In contrast, Sierra Nevada bighorn males weigh up to only 200 lb (90 kg) and females to 140 lb (60 kg). Males' horns can weigh up to 30 lb (14 kg), as much as the rest of the bones in the male's body.

## Range and Lifestyle

Rocky Mountain bighorns inhabit the mountains from Canada south to New Mexico. They are relatives of goats, and have balance-aiding split hooves and rough hoof bottoms for natural grip. These attributes, along with keen vision, help them move easily about rocky, rugged mountain terrain. Wild sheep live in social groups, but rams and ewes typically meet only to mate. Rams live in bachelor groups and females live in herds with other females and their young rams. When fall mating arrives, rams gather in larger groups and ram fighting escalates. Usually only stronger, older rams (with bigger horns) are able to mate.

In winter, bighorn herds move to lower-elevation mountain pastures. In all seasons, these animals eat available grass, seeds, and plants. They regurgitate their food to chew it as cud before swallowing it for final digestion. Lambs are born each spring on high, secluded ledges protected from bighorn predators such as wolves, coyotes, and mountain lions—though not the golden eagles which target lambs. Young can walk soon after birth, and at one week old each lamb and its mother join others in a herd. Lambs are playful and independent, though their mothers nurse them occasionally for four to six months.

## Gallery

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