Have you ever heard of thinhorn sheep?

Thinhorn refers to the rare Stone’s sheep of northwest Canada and more common Dall’s sheep that live in Canada, the Yukon and Alaska. They are distantly related to the bighorn sheep that live in Montana, but — as their name indicates — they have thinner horns than Rocky Mountain bighorn sheep.

Although related, Stone and Dall sheep look different. Stone sheep have “gray, brown or black coats with white noses, bellies and rump patches,” according to the Yukon Department of the Environment. “Whereas Dall’s sheep are typically pure white.”

Dall sheep have white fur because they live farther north in snowy areas where a white coat helps them hide from predators.

When the two thinhorn sheep breed with each other the lamb is called a Fannin’s sheep. This explains why Fannin’s sheep have a gray or tan patch on their back that looks like a saddle. The rest of their fur is white.

Stone’s sheep are smaller than bighorns. A bighorn ram may weigh up to 300 pounds, its large curving horns may weigh 30 to 40 pounds. In comparison, a big Stone ram may weigh only 200 pounds while its horns weigh around 20 pounds.

The Stone’s sheep population, estimated at around 2,500, is small compared to its cousin the Dall’s sheep, which numbers around 20,000. Scientists are now saying that,  based on genetic tests, there are even fewer Stone’s sheep than previously thought.

"When correctly classified as Dall's sheep, our results show that the rarer subspecies is even rarer than we once thought, about 20 percent less than previously thought," said Zijian Sim of the University of Alberta.

— Brett French, french@billingsgazette.com

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