This species is found in the United States (Alaska), through to northern British Columbia, Yukon, and Northwest Territories (Canada).
Thinhorn sheep are represented by two subspecies in Canada. Dall’s 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. Stone’s sheep (O. d. stonei) is found only in Canada, and here its range extends from an area of integration with Dall’s 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, Dall’s 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).
The total population of thinhorn sheep in Canada is ca. 41,500 animals. Of this total, 27,000 are Dall’s sheep (with 19,000 in the Yukon (Hoefs and Barichello, 1985), 7,500 in the Northwest Territories (Poole and Graf, 1985; unpubl. data), and 500 in British Columbia (J. Elliot, in litt. to D. Hebert)), and 14,500 Stone’s sheep (with 3,000 in the Yukon (Hoefs and Barichello, 1985), and 11,500 in British Columbia (J. Elliot, in litt. to D. Hebert)).
This species has broad habitat preferences in the arctic and sub-arctic regions but occurs mostly in high mountain ranges. They typically inhabit dry mountainous regions and select subalpine grasslands and shrublands (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), 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).
This species is primarily affected by hunting, both for sport and subsistence, but for the most part this is tightly managed, and hunting is not believed to constitute an overall threat to the species.
In Canada, three National Parks (Kluane, Nahanni and Ivvavik), covering 36,976 km², protect ca. 3,200 Dall’s sheep (i.e., ca. 12% of the estimated total Canadian population) from industrial development and sport-hunting. Territorial wildlife reserves include no provision for habitat protection, but ca. 2,700 Dall’s sheep within these reserves are off limits to non-aboriginal hunters. Protected areas in British Columbia are strictly managed to allow a limited harvest of thinhorn sheep. Management of thinhorn sheep populations involves regulating annual licensed harvests, habitat enhancement (usually through burning), limited predator control, and involvement in the environmental screening process with respect to access, mining, forestry and agriculture on crown land. Aboriginal peoples are permitted by Yukon and Northwest Territories Acts (1898) to hunt thinhorn sheep for subsistence purposes within and outside national and territorial parks, and wildlife reserves. Similar treaty rights were granted to aboriginal people in northeastern British Columbia in 1906. A recent federal court ruling in British Columbia has inferred that all Canadian Indians have subsistence rights, subject to conservation considerations. Outside national parks, licensed harvest of thinhorn sheep is regulated by territorial or provincial wildlife acts and associated regulations. Status Indians are not required to possess a hunting license. Only in Yukon is the aboriginal sheep harvest systematically estimated, and overall, it is believed to be minimal. Adult males with horns of 4/5 curl (Northwest Territories) or full curl (Yukon and British Columbia) can be hunted by non-aboriginal hunters under license, with mandatory reporting of kills. Wildlife regulations can be amended annually with ministerial consent, and are strictly enforced. Typically, trends in the number and age of males killed by licensed hunters provide the basis for more restrictive management. Quotas or limited-entry hunting, that set a ceiling on the harvest or ‘which restrict hunting opportunities, have been implemented in some areas to further control hunting pressure. The licensed annual harvest of thinhorn sheep typically averages 280 in Yukon (Hoefs and Barichello, 1985), 200 in the Northwest Territories (Poole and Graf, 1985) and 500 in British Columbia (J. Elliot, unpubl. data). Guided, non-resident hunters account for about 70% of the total licensed thinhorn sheep harvest.
Join me in the Yukon in 2015 to photograph Thinhorn sheep and other animals. All the details of that trip can be found here.
All data on this post comes from the Red List for Threatened Species