Zion Bighorn Sheep

by Robert Bales

Title

Zion Bighorn Sheep

Artist

Robert Bales

Medium

Photograph - Photo

Description

The bighorn sheep (Ovis canadensis) is a species of sheep in 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. Conservation efforts (in part by the Boy Scouts) have restored the population.
Ovis canadensis is one of three species of mountain sheep in North America and Siberia; the other two species being Ovis dalli, which includes Dall sheep and Stone's sheep, and the Siberian snow sheep Ovis nivicola. Wild sheep crossed the Bering land bridge from Siberia during the Pleistocene (about 750,000 years ago) and subsequently spread through western North America as far south as Baja California and northwestern mainland Mexico. Divergence from their closest Asian ancestor (snow sheep) occurred about 600,000 years ago. In North America, wild sheep have diverged into two extant species�Dall sheep, which occupy Alaska and northwestern Canada, and bighorn sheep, which range from southern Canada to Mexico. However, the status of these species is questionable given that hybridization has occurred between them in their recent evolutionary history.
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�100 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.

Zion National Park is located in the Southwestern United States, near Springdale, Utah. A prominent feature of the 229-square-mile (590 km2) park is Zion Canyon, which is 15 miles (24 km) long and up to half a mile (800 m) deep, cut through the reddish and tan-colored Navajo Sandstone by the North Fork of the Virgin River. The lowest elevation is 3,666 ft (1,117 m) at Coalpits Wash and the highest elevation is 8,726 ft (2,660 m) at Horse Ranch Mountain. Located at the junction of the Colorado Plateau, Great Basin, and Mojave Desert regions, the park's unique geography and variety of life zones allow for unusual plant and animal diversity. Numerous plant species as well as 289 species of birds, 75 mammals (including 19 species of bat), and 32 reptiles inhabit the park's four life zones: desert, riparian, woodland, and coniferous forest. Zion National Park includes mountains, canyons, buttes, mesas, monoliths, rivers, slot canyons, and natural arches.

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April 22nd, 2013

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