Dall's sheep is one of the most sought after of northern mammals by hunters and naturalists alike. The striking white pelage and amber-colored horns, combined with the sheep's natural grace and agility, are a match for the spectacular beauty of their mountain home.
Dall's sheep, Ovis dalli dalli, is the northernmost of three subspecies of the thinhorn sheep (Ovis dalli) of Alaska, Yukon, and northern British Columbia. These northern sheep are found in rugged mountainous areas across Alaska and Yukon and into the Northwest Territories. The two other subspecies are the darker-colored Stone sheep (Ovis dalli stonei) of south-central Yukon and north-central British Columbia, and the Kenai sheep (Ovis dalli kenaiensis) found only on the Kenai Peninsula of Alaska. In eastern Siberia and Kamchatka, the closely related snow sheep, Ovis nivi-cola, occupies a similar habitat. The total population of Dall's sheep is about 86,000 (70,000 in Alaska, 9000 in Yukon, 7000 in Northwest Territories, and 200 in British Columbia).
In Arctic North America, Dall's sheep inhabit much of the Brooks Range of northern Alaska, with about 9000 sheep residing in the Arctic National Wildlife Refuge. At the western edge of this range, in the Arctic regions of Yukon, a small population of about 200 sheep is found in the British Mountains near the Firth River in Ivvavik National Park. About 1400 Dall's sheep live in the Richardson Mountains on the border of Yukon and the Northwest Territories, west of the Mackenzie River.
The wide-flaring, light-colored horns grow throughout life. Horn growth may vary from year to year and is influenced by environmental factors such as precipitation. The age of adult males particularly can be estimated by counting the annual growth rings. The horn tips of older males often become worn down or "broomed." The female's horns are smaller and retain their sharp tips. Females are also lighter in weight than males (average females weigh about 50 kg, males about 80 kg) and smaller (the average shoulder height of females is 84 cm, males 93 cm).
The creamy-white coat of Dall's sheep is made up of an undercoat of fine wool covered by a protective coat of long, stiff, hollow guard hairs. In winter, this white coat may be up to 5 cm thick.
Dall's sheep were first identified as a separate species by American zoologist and explorer E.W. Nelson in 1884. He named this "new" sheep after William Healy Dall (1845-1927), a zoologist who undertook many surveying and exploring trips to Alaska in the late 1800s.
In the North Alaska Inupiat dialect, Dall's sheep are imnaik and in the Kobuk River dialect, ipnaik. In the northern Yukon, the Vuntut Gwich'in name for Dall's sheep is divii. Among the common English names given to this sheep are white sheep, Dall's sheep, white mountain sheep, and in French, mouflon de Dall.
Dall's sheep have been used by people in North America for many thousands of years. Sheep blood has been detected in residues on tools from 6000 to 1000 years old. Traditionally, sheep horns were used to make bowls, spoons, and tool handles. Hides were made into thin cords for snowshoe netting. Before the arrival of the Hudson's Bay Company, Vuntut Gwich'in from Old Crow, Yukon, traveling to the Arctic coast in Alaska and Yukon to trade muskrat skins, also traded Dall's sheep meat and hides with the Inupiat and Inuvialuit who lived along the coast. In historic times, whalers, explorers, trappers, and prospectors also used Dall's sheep for food.
During the International Boundary survey of 1911-1912, scattered bands of sheep were seen on the north slopes of the British Mountains, Yukon, to within 24 km of the Arctic coast. Large numbers of old sheep skulls and bones were found on the Arctic slopes, suggesting a decrease in population due to disease or hunting to support whalers wintering at Herschel Island.
In order to find suitable feeding areas where their usual diet of grasses, sedges, and low shrubs is accessible, Dall's sheep move seasonally between ranges. The restricted winter feeding areas are influenced by snow accumulation. During most of the year, female Dall's sheep travel apart from the males, living with their young in small bands. Male sheep may use as many as six different ranges by season: prerutting, rutting, mid-winter, late winter-spring, salt-lick, and summer ranges. Ranges used by adult females are less complex: winter, spring, lambing, and summer.
Adult male and female Dall's sheep come together during the rut or breeding season in November and December. Rutting males fight for the possession of receptive females, using their horns in social encounters ranging from mild threats to elaborate and impressive head-clashing combat. The large dominant males do most of the mating: courting, defending, and copulating with several females.
Lambs are born in early to mid-May following a gestation period of 171 days. Births are highly synchronized and take place in secluded sites on steep slopes or cliffs. Lambs are able to follow their mothers over rough ground when only a day old. Suckling ceases by about 4 months of age. Females usually bear a single lamb annually and are known to live up to a maximum of 20 years in the wild.
Like other ungulates, Dall's sheep are usually infected with several parasites and other disease-causing organisms. Although lungworms are common, die-offs due to lungworm infestations have not been observed in this sheep. Wolves, coyotes, grizzly bears, and black bears all prey on adult and young sheep. Lambs may also be taken by lynx and golden eagles. Dall's sheep live in steep, rugged terrain where they can avoid predators, but some sheep also die from avalanches and accidental falls. Besides accident, disease, and predation, Dall's sheep can be killed by a combination of factors including deep snow, low temperatures, high population density, and low-quality food.
Subsistence hunting (by Inupiat, Gwich'in, and Inuvialuit hunters) and sport hunting are closely regulated. Sport hunting is restricted to older adult males and usually requires guides or outfitters. The harvest of Dall's sheep is restricted to a small portion of the population.
The major habitat requirement for sheep in the northern part of their range seems to be the need for appropriate escape terrain. Salt-licks where natural calcium is available can be important seasonally.
Loss of habitat due to human disturbance and development is not yet a problem for sheep in the north, but the impact of new northern pipeline proposals and increased tourism on Dall's sheep are issues that need to be carefully considered.
David R. Gray
See also Brooks Range; Herschel Island; Inupiat; Inuvialuit; Sheep; Sheep Farming
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