Dall's sheep occur in western Canada and the United States. They can be found throughout the mountain ranges of northeast, central and southern Alaska, as well as in the Yukon Territory, the northwest corner of British Columbia, and southwest of the Mackenzie River in the Northwest Territories (Valdez, 1982).

There are two subspecies, Ovis dalli dalli and Ovis dalli stonei. Ovis dalli dalli includes populations found in most of Alaska and the Yukon territories, extreme northwest British Columbia, and the Kenai Peninsula of Alaska. Ovis dalli stonei includes populations found in south-central Yukon and north-central British Columbia (Wilson and Ruff, 1999).

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Extensive areas of Brooks and Alaska ranges in Alaska, Kenai Peninsula, and MacKenzie and Rocky mountains in western Canada (Yukon and Northwest Territories south to Peace River in British Columbia); many southern populations are isolated.

Ovis dalli are the only species of thinhorn mountain sheep (Nichols and Bunnell, 1999). The horns are conspicious and sexually dimorphic. They can be either amber or almost transparent. Females have slender horns, while male horns are massive, flaring, and curled. Horns grow annually in both sexes, but, after the first 4-5 years, male horn growth increases greatly and can end up constituting 8-10% of their total body weight (Bowyer and Leslie, 1992). Horns grow in spring, summer, and into early fall when the growth slows down. Horn growth stops during the winter. This start and stop growth pattern results in a pattern of rings on the horns. These rings are called annuli, and can be used to determine age. As rams mature their horns form a circle. A full circle can be reached within about 8 years (Heimer, 1994).

Body size is also sexually dimorphic. Males are about 40% heavier than females, and continue to grow 2 years beyond female maturity at 4 years. Males can weigh between 73 to 113 kg, while females weigh between 46 to 50 kg. Body length also varies from 1.3 to 1.8 m in males and 1.32 to 1.62 m in females. Tail length is between 70 to 115 mm in males and between 70 to 90 mm in females (Wilson and Ruff, eds., 1999).

The pelage consists of a fine wool undercoat and stiff, long, and hollow guard hairs. The winter coat can be thicker than 5 cm (Bowyer and Leslie Jr., 1992). The subspecies, Ovis dalli dalli, has a pure white or creamy white pelage and tail, although variation is present. Some individuals have a black tail, others have slight grey patches often in the middle of the back. Ovis dalli stonei has a grey to black pelage. The inside of the ears are white, while the outsides are grey. The belly is white, as are the backs of the legs. They also have a white rump patch, and a black tail (Shackleton, 1999). A moult occurs from March to July, with mature males moulting before the females, young, and older individuals (Bowyer and Leslie Jr., 1992).

The skin of the face and rostrum is thickened, especially in males. The males also have a double layer of bone on their skulls which allows them to absorb heavy impacts suffered during battles between males (Bowyer and Leslie, 1992).

Dental formula is I 0/3, C 0/1, P 3/3, M 3/3, with 30 teeth total (Bowyer and Leslie, 1992).

Range mass: 46 to 113 kg.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger; ornamentation

Length: 153 cm

Weight: 90000 grams

• Terrestrial

Dall's sheep have broad habitat preferences in the arctic and sub-arctic regions but are largely alpine animals, living in high mountain ranges. Generally, they inhabit dry mountainous regions and select sub-alpine grass and low shrub communities (Bowyer and Leslie, 1992). They are dependent upon steep, rugged cliffs and outcrops that provide escape terrain from predators. They use nearby open grass and meadows for feeding. In winter they prefer areas with light snowfall and strong winds that remove snow and expose forage (Nichols and Bunnell, 1999)

Most populations occupy distinct summer and winter ranges, although some are sedentary. Migrations are correlated with snow depth, temperature and plant phenology. Most of the year is spent in the winter range in wind-swept areas that expose forage (Bowyer and Leslie, 1992).

Adult males can occupy six seasonal home ranges: pre-rutting, rutting, midwinter, late winter and spring, salt-lick, and summer (Bowyer and Leslie, 1992). Females usually have four ranges: winter, spring, lambing, and summer. Lambs inherit home ranges from older individuals and they return annually to these inherited ranges (Bowyer and Leslie, 1992).

There seems to be no competition with other ungulates in their ranges for food or space. Wolves (Canis lupus) prey on the sheep in regions where their ranges overlap and may decrease the populations severely if no other prey is available. Coyotes (Canis latrans), golden eagles (Aquila chrysaetos), lynx (Lynx canadensis), grizzly bears (Ursus arctos), black bears (Ursus americanus), and wolverines (Gulo gulo) are also predators. Deaths from accidental falls and avalanches are also common (Wilson and Ruff, 1999). Deep snow, low temperatures, high population density, disease, low-quality forage, and predation are primary sources of mortality, especially among lambs (Bowyer and Leslie, 1992).

Terrestrial Biomes: mountains

Comments: Typically in semiopen, precipitous terrain with rocky slopes, ridges, and cliffs or rugged canyons; dry mountainous terrain, subalpine grass-low shrub communities. Attracted to mineral licks. In winter, attracted to areas with little or no snow cover. Females rely on precipitous mountain areas for escape cover during lambing period (Lawson and Johnson 1982).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Migrates to higher elevations in spring, to lower elevations in fall. Exhibits high degree of fidelity to seasonal home ranges. Some populations do not migrate between seasonal ranges.

Dall's sheep are herbivorous, grazing primarily for grasses and sedges. They inhabit various habitats with many potential forage species. They can consume between 50-120 species of vegetation. In summer, food is abundant and a wide variety of plants is consumed. In the winter, diet is much more limited, nevertheless, 10-15 species are consumed year long.

They select grasses, sedges and forbs when available, but also ingest lichens and mosses in smaller quantities (Nichols and Bunnell, 1999). Wheatgrass, fescues, bluegrass, and sedges are important foods, while clover, peavine, lupines, pasture sage, dwarf willow, and cinquefoil are eaten when available (Blood, 1999).

In the winter, diet is influenced by accumulation of snow on the ranges, and consists mostly of dry, frozen grass, and sedge stems that are uncovered where snow is blown off, and more lichens and mosses than in other seasons (Bowyer and Leslie, 1992). Mineral licks of calcium phosphate or calcium magnesium concentrate are also important in the diet, especially in the spring and summer, to compensate for mineral deficiencies (Bowyer and Leslie, 1992)

Comments: Eats mainly grasses (fescues), sedges, and forbs in summer. Willow, horseweed (Erigeron), and alpine fireweed important in spring and summer. Relishes horsetail and Richardson's saxifrage. Woody plants important in winter. Uses mineral licks high in calcium-phosphate or calcium-magnesium.

10,000 to >1,000,000 individuals

Comments: Reports in the 1970s and 1980s included the following population estimates: 70,000 subspecies DALLI in Alaska, 9000 in Yukon, 7000 in Northwest Territories, and 200 in British Columbia; 3000 subspecies STONEI in Yukon, 10,000-11,000 in British Columbia (see Bowyer and Leslie 1992).

Gregarious. Up to 19-23 individuals per sq km on northern winter ranges. Adult bands are segregated by sex. Largest bands are composed of females and young; males are more solitary (Lawson and Johnson 1982). Mortality of young may be 40-50% by end of first winter in populations near carrying capacity. Severe winters may cause population declines. Wolf predation may limit some populations. Maximal annual rate of increase for unhunted populations is 11-18%. Generally does not compete with other native ungulates, but feral horses may compete. See Bowyer and Leslie (1992).

Comments: Little nocturnal activity (Lawson and Johnson 1982).

Average lifespan

Status: captivity: 19.6 years.

Rams can sire lambs at 18 months but do not usually mate successfully until they acheive social dominance and adult size at 5-7 years of age. Females are sexually mature at 30 months and have their first lamb by age 3 or 4. They produce lambs annually after that (Bowyer and Leslie, 1992).

Lambs are born in late May or early June. Ewes seek solitude and protection in the most rugged cliffs to bear their lamb. Ewes give birth and the mother-lamb pair remains in the cliffs until the lambs are strong enough to travel. Lambs begin to feed on vegetation within two weeks of birth, and are weaned after three to five months, usually by October (Heimer, 1994).

Gestation lasts about 175 days, after which a single lamb is born. Twins are rare (Bowyer and Leslie, 1992). The young weigh between 3-4 kg at birth. Females lick and paw the lambs soon after birth (Shackleton, 1999). Lambs can stand for the first time 15-32 minutes after birth, and are able to travel with their mother within 24 hours. The young grow rapidly, and can achieve 27-30 kg by 9 months of age (Bowyer and Leslie, 1992).

The annual rate of increase can be 11-18% in an unhunted population, but mortality of lambs can reach 40-50% by their first winter in populations nearing carrying capacity (Bowyer and Leslie, 1992)

Range number of offspring: 1 to 2.

Average gestation period: 5.7 months.

Range weaning age: 4 to 5 months.

Average birth mass: 2819 g.

Average gestation period: 173 days.

Average number of offspring: 1.

Average age at sexual or reproductive maturity (male)

Sex: male: 639 days.

Average age at sexual or reproductive maturity (female)

Sex: female: 684 days.

Parental Investment: altricial ; post-independence association with parents

Monestrous. Breeds November-December. Gestation lasts 5.5-6 months. Usually single young is born late April-late June; most births before end of May (peak in May in central Alaska). Young are able to travel with mother within 24 hours, weaned in 3-5 months. Most females breed at 1 year. Females may not breed every year, especially in low quality habitats. Males physiologically mature as early as second year, but generally are precluded from breeding until several years old by older males.

Federal, state, and provincial governmental agencies are responsible for the management of Dall's sheep populations. Human activities such as mineral exploration, road construction, and aircraft harassment disrupt populations of Dall's sheep (Bowyer and Leslie, 1992). In British Columbia range burning is used to slow population declines by improving the quality of forage in winter (Bowyer and Leslie, 1992). Most of their range remains remote and pristine and populations have remained relatively unaffected by humans . However, wild sheep face a precarious future because they are adapted to a limited habitat that is becoming increasingly fragmented (Nichols and Bunnell, 1999).

Populations are threatened by trophy harvest (especially adult rams), hunting in parks and reserves, and, to somel extent, subsistence hunting by native peoples (Bowyer and Leslie, 1992). Only two populations in Alaska exist for which subsistence hunting is allowed. Annual trophy harvest is restricted to mature rams. Most adult males are harvested by nonresidents who are required to pay special fees, hire guides and outfitters, and who are restricted to specific management areas (United States) or outfitter units (Canada) (Bowyer and Leslie, 1992).

In British Columbia, Ovis dalli dalli have been put on the Blue List of species at risk due to their low number in that province, approximately 500 sheep. Ovis dalli stonei have been downlisted from the Blue List to the Yellow List, due to improvement in population numbers (Shackleton, 1999).

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N4 - Apparently Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Comments: Population decline in southwestern Yukon was attributed to impact of feral horses (Hoefs and Bayer 1983). Dalle-Molle and Van Horn (1991) noted that, in some circumstances, vehicle traffic may interfere with seasonal migrations.

Management Requirements: Most of range is remote and pristine, but burning of subalpine ranges has been used to improve forage in British Columbia (see Bowyer and Leslie 1992).

In Alaska, survival of young males and production of lambs and yearlings did not appear to be affected by harvest of old males (Murphy et al. 1990). See Bowyer and Leslie (1992) for general comments on hunting management.

There are no known negative effects of Dall's sheep.

Native hunters hunt these sheep for subsistence. However, Dall's sheep are not as popular as other species, because they are difficult to hunt and do not provide as much meat as larger arctic species (e.g. caribou) (Shackelton, 1999).

Positive Impacts: food ; body parts are source of valuable material

Comments: Hunting, primarily for trophies, takes a very small percentage of the total population (Bowyer and Leslie 1992).

Comments: Subspecies kenaiensis may not be valid; may represent one end of a size cline in subspecies dalli (see Bowyer and Leslie 1992). Grubb (in Wilson and Reeder 2005) did not recognize kenaiensis as a valid subspecies.

See Georgiadis et al. (1991) for a phylogeny of the Bovidae based on allozyme divergence among 27 species. See Kraus and Miyamoto (1991) for a phylogenetic analysis of pecoran ruminants (Cervidae, Bovidae, Moschidae, Antilocapridae, and Giraffidae) based on mitochondrial DNA data.