Mammal Species of the World
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Thinhorn sheep are represented by two subspecies in Canada. Dalls sheep (O. d. dalli) occurs west of the Mackenzie River throughout the Richardson and the Mackenzie mountains on the Yukon-Northwest Territories border, throughout the mountainous regions in Yukon, and south into the extreme northwest corner of British Columbia. Stones sheep (O. d. stonei) is found only in Canada, and here its range extends from an area of integration with Dalls sheep in south-central Yukon (Cassiar and Pelly mountains, MacArthur ranges, and White Mountains), south to the Cassiar range (ca. 56 N) in British Columbia. In Alaska, Dalls sheep occupies drier areas of the Kenai, Chugach, Wrangell, and Talkeeetna mountains, and the Alaska and Brooks ranges. Scattered populations also occur in the low mountains between the Tanana and Yukon rivers. Separate herds are not usually identified in these large areas. A recent genetic analysis has confirmed the presence of two subspecies (Worley et al. 2004).
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
Regularity: Regularly occurring
Type of Residency: Year-round
Regularity: Regularly occurring
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
Size in North America
Range: 1.3-1.8 m males; 1.3-1.6 m females
Range: 73-110 kg males; 46-50 kg females
Habitat and Ecology
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), grizzly bears (Ursus arctos), 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).
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).
Life History and Behavior
Perception Channels: tactile ; chemical
Comments: Little nocturnal activity (Lawson and Johnson 1982).
Status: captivity: 19.6 years.
Lifespan, longevity, and ageing
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.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
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.
Molecular Biology and Genetics
Statistics of barcoding coverage: Ovis dalli
Public Records: 0
Specimens with Barcodes: 2
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2000Lower Risk/least concern (LR/lc)
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
National NatureServe Conservation Status
Rounded National Status Rank: N4 - Apparently Secure
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
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.
In the United States, Dalls sheep occurs in eight Federal protected areas in Alaska: Denali, Gates of the Arctic, Lake Clark, Noatak, and Wrangell-St. Elias National Parks; Arctic, Kenai, and Yukon Flats National Wildlife Refuges; and Yukon-Charley Rivers National Preserve. Seven of these areas are among the largest such reserves in the United States. About 70% of all Dalls sheep in Alaska occur in hunted areas. Most harvest is regulated by the state, though federal regulations are being used for some federal lands. Under Alaska Department of Fish and Game regulations, most harvesting of Dalls sheep is conservative, with only mature males being hunted. Dalls sheep are prized as big game trophies. Primarily males are hunted, with around 1,200 to 1,300 mature males taken each year. Native subsistence hunting is allowed in some areas and may threaten local populations. The Department monitors populations, and with other agencies, conducts research on the species. Dalls sheep is rated secure in the US because it is abundant, widely distributed throughout its native range, and occurs in many areas protected such as national parks, preserves, and wildlife refuges.
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.
Relevance to Humans and Ecosystems
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).
The Dall sheep (originally Dall's sheep), Ovis dalli, is a species of sheep native to northwestern North America, ranging from white to slate brown in color and having curved yellowish brown horns. Its closest relative is the more southern subspecies, Stone sheep (also spelled Stone's sheep) (Ovis dalli stonei), which is a slaty brown with some white patches on the rump and inside the hind legs.
Research has shown the use of these subspecies designations is questionable. Complete colour integradation occurs between white and dark morphs of the species with intermediately coloured populations, called Fannin sheep (Ovis dalli fannini), found in the Pelly Mountains and Ogilvie Mountains of Yukon Territory. Mitochondrial DNA evidence has shown no molecular division along current subspecies boundaries, although evidence from nuclear DNA may provide some support. Also at the species level, current taxonomy is questionable because hybridization between Ovis dalli and Ovis canadensis has been recorded in recent evolutionary history.
The latter half of the Latin name dalli is derived from William Healey Dall (1845–1927), an American naturalist. The common name Dall sheep or Dall's sheep is often used to refer to the species Ovis dalli. An alternative use of common name terminology is that thinhorn sheep refers to the species Ovis dalli, while Dall's sheep and Stone's sheep refer to subspecies Ovis dalli dalli and Ovis dalli stonei, respectively.
The sheep inhabit the subarctic mountain ranges of Alaska, the Yukon Territory, the Mackenzie Mountains in the western Northwest Territories, and central and northern British Columbia. Dall sheep are found in relatively dry country and try to stay in a special combination of open alpine ridges, meadows, and steep slopes with extremely rugged ground in the immediate vicinity, to allow escape from predators that cannot travel quickly through such terrain.
Male Dall sheep have thick curling horns. The females have shorter, more slender, slightly curved horns. Males live in bands which seldom associate with female groups except during the mating season in late November and early December. Lambs are born in May.
During the summer when food is abundant, the sheep eat a wide variety of plants. The winter diet is much more limited, and consists primarily of dry, frozen grass and sedge stems available when snow is blown off, lichen and moss. Many Dall sheep populations visit mineral licks during the spring, and often travel many miles to eat the soil around the licks.
Dall sheep can often be observed along the Alaska Highway at Muncho Lake in British Columbia, along the Seward Highway South of Anchorage, AK., within Denali National Park and Preserve (which was created in 1917 to preserve Dall sheep from over-hunting), at Sheep Mountain in Kluane National Park and Reserve, as well as near Faro, Yukon (Fannin's sheep).
- Festa-Bianchet, M. (2008). Ovis dalli. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 April 2009. Database entry includes a brief justification of why this species is of least concern.
- Sheldon, C. 1911. The Wilderness of the Upper Yukon. First edition. Charles Scribner’s Sons, New York.
- Loehr, J., K. Worley, A. Grapputo, J. Carey, A. Veitch and D. W. Coltman (2006). "Evidence for cryptic glacial refugia from North American mountain sheep mitochondrial DNA". Journal of Evolutionary Biology 19: 419–430. doi:10.1111/j.1420-9101.2005.01027.x. PMID 16599918.
- Worley, K., Strobeck, C., Arthur, S., Carey, J., Schwantje, H., Veitch, A. and Coltman, D.W. (2004). "Population genetic structure of North American thinhorn sheep Ovis dalli". Molecular Ecology 13 (9): 2545–2556. doi:10.1111/j.1365-294X.2004.02248.x. PMID 15315669.
- Home Page, Alaska Department of Fish and Game. Adfg.state.ak.us. Retrieved on 2011-09-16.
|Wikimedia Commons has media related to Ovis dalli.|
- A.W.F. Banfield (1974). The Mammals of Canada. University of Toronto Press. ISBN 0-8020-2137-9
- Ovis dalli. Brower and Leslie
- Smithsonian Institution - North American Mammals: Ovis dalli
Names and Taxonomy
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.