This species occurs mostly in high mountain ranges. They typically inhabit dry mountainous regions and select subalpine grasslands and shrublands (Bowyer and Leslie 1992). Jex et al. (2016) described Thinhorn Sheep habitat as open yet rugged terrain that allowed sheep to forage efficiently while also supporting detection and evasion of predators. Thinhorn Sheep habitats must contain adequate amounts of forage, escape terrain, birthing, loafing or respite areas, and unobstructed corridors through which they can move during their annual cycles. While rugged lambing habitat is essential, thinhorn populations are most sensitive to availability of high-quality ranges during winter, when animals are physiologically and nutritionally most challenged (Jex et al. 2016). 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, plant phenology and regular movements to mineral licks. Most of the year is spent in the winter range in wind-swept areas that expose forage (Bowyer and Leslie 1992). Stochastic weather events associated with global climate change and more cyclical climatic influences such as Pacific Decadal Oscillation can affect precipitation, temperature regimes, soil moisture, plant growing conditions and have the potential to also affect individual growth and population levels of Thinhorn Sheep (Hik and Carey 2000).

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. Thinhorn Sheep have a broad complement of predators within their distribution, among which are wolverines Gulo gulo, golden eagles Aquila chrysaetos, bears (black Ursus americanus and grizzly Ursus arctos), lynx Lynx canadensis, wolves Canis lupus, and coyotes Canis latrans. Stone’s sheep may also fall prey to cougars Puma concolor, but those felids are generally absent or occur at very low densities throughout the majority of Thinhorn Sheep range (Jex et al. 2016). Lohuis (2016) found coyotes and golden eagles to be responsible for approximately 40% and 20% of lamb predation events on collared lambs, respectively. Deep snow, low temperatures, high population density, disease and parasites, low-quality forage, and predation are primary sources of mortality, especially among lambs (Bowyer and Leslie 1992 and Jex et al. 2016). In addition, increasing pressures associated with exploitative, interference and apparent interspecific competition can be influenced by human interventions and expanded ranges of other species leading to negative impacts on Thinhorn Sheep at localized scales (Jex et al. 2016).

This species is found in the United States of America (USA) (Alaska), through the Yukon and Northwest Territories, to northern British Columbia (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 northwest portion of British Columbia’s St. Elias and Coast mountains. Stone’s sheep O. d. stonei is found only in Canada with British Columbia hosting the vast majority of the global population.  Its overall range extends from an area of integration with Dall’s sheep along the southern border in south-central Yukon (Cassiar and Pelly mountains), south and southeast through the Cassiar, Kaska, northern Rocky, and Skeena and Omineca mountains 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. A recent genetic analysis has re-confirmed the presence of the two subspecies (Sim et al. 2016), with Dall’s sheep being grouped into 5 discrete genetic subpopulations and Stone’s into 3 genetic subpopulations (Sim et al. 2018); this work has led to revisions to previous subspecies distribution mapping.

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. Several protected areas in British Columbia allow a limited harvest of Thinhorn Sheep. Management 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) and in British Columbia, to hunt Thinhorn Sheep for subsistence and cultural 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. 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 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, where a decline in ram horn size has been observed in the Peace area with intense harvest, and attributed to an evolutionary consequence of selective hunting (Douhard et al. 2016). No change was observed in the Skeena area where harvest intensity is lower. Guided, non-resident hunters account for about 70% of the total licensed Thinhorn Sheep harvest.

In the USA, Dall’s 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 USA. About 70% of all Dall’s 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 Dall’s sheep is restricted to mature males. About 1,200 to 1,300 mature males are taken each year. Native subsistence hunting is allowed in some areas. The Department monitors populations, and with other agencies, conducts research on the species. Dall’s sheep is rated secure in the US because it is abundant, widely distributed throughout its native range, and occurs in many national parks, preserves, and wildlife refuges.