On a summer day we are hiking up a treeless, rocky hillside in the Burwash uplands of Kluane. As we crest a ridge we see a herd of a dozen Dall's sheep just a hundred yards away. The group immediately bolts, disappearing off the backside of the ridge.
The sheep inhabit mountain ranges of Alaska, the Yukon, the Northwest Territories, and central and northern British Columbia. Dall's sheep favor relatively dry country with a combination of open alpine ridges, meadows, and steep slopes to allow escape from predators that cannot travel as quickly through rugged terrain.
These wild sheep native to northwestern North America are often called thinhorn sheep, and Dall's sheep and Stone sheep are considered to be subspecies, although genetically all are very similar. Bighorn sheep are a closely related species found further south in the American west. Bighorn sheep populations were profoundly impacted by diseases introduced by European livestock.
Is it Dall sheep or Dall's sheep? Both are commonly used. Most scientific journals require the use of the possessive adjective with the apostrophe ess - Dall's sheep. The animals are named for William Healy Dall, a renowned American naturalist who explored Alaska in the decades following the purchase from Russia.