Dall sheep

The Dall's sheep, (or Dall sheep), Ovis dalli dalli, is the more northern subspecies of thinhorn sheep, Ovis dalli sp. These sheep are native to northwestern North America and survived recent glaciations in refugia located in Alaska, Yukon and north-western British Columbia.

Dall's sheep
ram
ewe
both in Denali National Park in Alaska
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Bovidae
Subfamily: Caprinae
Genus: Ovis
Species:
O. dalli
Binomial name
Ovis dalli
Nelson, 1884
Subspecies
  • O. d. dalli Dall sheep
  • O. d. stonei Stone sheep

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.[2] 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,[3] although evidence from nuclear DNA may provide some support.[4] Current taxonomy using mitochondrial DNA information may be less reliable due to hybridization between O. dalli and O. canadensis recorded in evolutionary history.[3]

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 subspecies O. d. dalli. Thinhorn sheep refers to the species O. dalli sp., which comprises two subspecies, Dall's sheep and Stone's sheep, O. d. dalli and O. d. stonei, respectively.

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. 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.

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.[5]

Primary predators of this sheep are wolf packs, coyotes, black bears, and grizzly bears; golden eagles are predators of the young. The 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).

  • Dall ewe and lamb group in Denali National Park
  • Two Dall sheep lambs
  • Stone sheep near roadway in British Columbia
  • Taxidermied specimens at the American Museum of Natural History

References
  1. Festa-Bianchet, M. (2008). "Ovis dalli". IUCN Red List of Threatened Species. 2008: e.T39250A10179389. doi:10.2305/IUCN.UK.2008.RLTS.T39250A10179389.en. Database entry includes a brief justification of why this species is of least concern.
  2. Sheldon, C. (1911). The Wilderness of the Upper Yukon. First edition. Charles Scribner's Sons, New York.
  3. Loehr, J.; K. Worley; A. Grapputo; J. Carey; A. Veitch; D. W. Coltman (2006). "Evidence for cryptic glacial refugia from North American mountain sheep mitochondrial DNA". Journal of Evolutionary Biology. 19 (2): 419–430. CiteSeerX 10.1.1.574.4471. doi:10.1111/j.1420-9101.2005.01027.x. PMID 16599918.
  4. Worley, K.; Strobeck, C.; Arthur, S.; Carey, J.; Schwantje, H.; Veitch, A. & Coltman, D.W. (2004). "Population genetic structure of North American thinhorn sheep Ovis dalli" (PDF). Molecular Ecology. 13 (9): 2545–2556. doi:10.1111/j.1365-294X.2004.02248.x. PMID 15315669. Archived from the original (PDF) on 29 March 2012.
  5. Home Page, Alaska Department of Fish and Game. Adfg.state.ak.us. Retrieved on 16 September 2011.

Further reading
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