Dall sheep

The Dall sheep (Ovis dalli), Dall's sheep or thinhorn sheep, is a wild sheep native to northwestern North America.
==Taxonomy and genetics==
Past research had shown the use of pelage-based subspecies designations was questionable. Complete colour intergradation occurs in both thinhorn sheep subspecies (i.e., Dall's and Stone's), ranging between white and dark morphs of the species. Intermediately coloured populations, called Fannin sheep were originally (incorrectly) identified as a unique subspecies (O. d. fannini) with distributions inhabiting in the Pelly Mountains and Ogilvie Mountains of the Yukon Territory.Sheldon, C. (1911). The Wilderness of the Upper Yukon. First edition. Charles Scribner's Sons, New York. Fannin sheep have more recently been confirmed as admixed individuals with predominantly Dall's sheep genetic origins. Previous mitochondrial DNA evidence had shown no molecular division along earlier subspecies boundaries, although evidence from nuclear DNA may provide some support. Current taxonomy using mitochondrial DNA information may be less reliable due to hybridization between O. dalli and O. canadensis recorded in evolutionary history.
Current genetics analyses using a genomewide set of single nucleotide polymorphisms (SNPs) has confirmed new subspecies range boundaries for both Dall's and Stone's sheep, updating the previous pelage-based and mitochondrial DNA classifications.
* Genome-wide set of SNPs reveals evidence for two glacial refugia and admixture from postglacial recolonization in an alpine ungulate .
* Management implications of highly resolved hierarchical population genetic structure in thinhorn sheep .
The specific name dalli, is derived from William Healey Dall (1845–1927), an American naturalist. The common name, Dall's sheep or Dall sheep is often used to refer to the nominate subspecies, O. d. dalli. The other subspecies, O. d. stonei, is called the Stone sheep.
==Natural history==
===Ecology===
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. Until the age of 3 years, male and female thinhorn sheep appear similar. Past that age, males are easily distinguished by their horns, which continue to grow steadily in the spring, summer, and early fall. This results in a start-and-stop growth pattern of rings called annuli. Annuli can be used to help determine age.
Males live in bands that seldom associate with female groups except during the mating season in late November and early December. Lambs are born in May.
While rams do clash horns, it is done to establish order, not over fights to possess ewes. Clashes occur throughout the year on an occasional basis, and increase in frequency just before the rut when rams encounter unfamiliar rams with similar horn sizes.
During the summer when food is abundant, the sheep eat a wide variety of plants. Their 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.Home Page, Alaska Department of Fish and Game. Adfg.state.ak.us. Retrieved on 16 September 2011.
Primary predators of this sheep are wolf packs, coyotes, black bears, and grizzly bears; golden eagles are predators of the young. Dall sheep has been known to butt gray wolves off the face of cliffs.
Dall sheep can often be observed along the Seward Highway South of Anchorage, Alaska, within Denali National Park and Preserve (which was created in 1917 to preserve Dall sheep from overhunting), at Sheep Mountain in Kluane National Park and Reserve, in the Tatshenshini Park Tatshenshini-Alsek Provincial Park in northwestern British Columbia, and near Faro, Yukon (Fannin's sheep).
==References==
==Further reading==
* Banfield, A.W.F. (1974). The Mammals of Canada. University of Toronto Press. 
* Ovis dalli. Brower and Leslie
* Smithsonian Institution - North American Mammals: Ovis dalli
* Western Association of Fish & Wildlife Agencies, Wild Sheep Working Group publication .
Category:Ovis
Category:Mammals of Canada
Category:Mammals of the United States
Category:Mammals described in 1884
Category:Taxa named by Edward William Nelson