The Ermine Adopts a White Coat for Winter

The ermine (scientific name: Mustela ermine), also known as the short-tailed weasel, is found in northern regions around the world. In North America, it occurs from Pennsylvania and Maryland north to New England, west across the Great Lakes states and Canada, from western Montana south in the Rocky Mountains to New Mexico, and from northern California north to Alaska. Although present throughout Pennsylvania (except perhaps in the southwestern corner), the ermine is much scarcer here than the closely related long-tailed weasel.

Adults are 9-15 inches in length, including a 1.6-3.2-inch tail; males are larger and heavier than females. Weights are 1.6-3.7 oz. Both sexes are smaller than corresponding sexes of the long-tailed weasel; a large male ermine is about the same size as a small female long-tailed. The ermine's bushy tail is shorter than that of the long-tailed weasel.

An ermine's pelt consists of soft, short underfur and long, coarse, glossy guard hairs. The sexes are colored alike, and immatures are similar to adults.

In summer, an ermine's upper-parts are dark brown, slightly darker on the head and legs. The chin and throat are white, and the underparts are white or cream-colored, extending down the insides of the legs and including the feet. The end third of the brown tail is black. In winter an ermine is white, tinged with yellow on the underparts and back. The tail tip remains black.

An ermine molts twice a year, in spring and autumn. The molts are triggered not by temperature but by amount of light per day, increasing in spring and decreasing in fall. Molts usually begin on the belly and spread to the sides and back, finishing with the tail. Aside for the varying, or snowshoe, hare, the Mustela weasles (3 species in Pennsylvania) are the only Pennsylvania mammals to turn white in winter.

The autumn molt (brown to white) begins in October and is usually complete by late November or early December. A molting ermine looks mixed brown and white. The white-to-brown spring molt runs from mid-March to late April.

Today's photo is courtesy of Stephen Nowers of the Anchorage Daily News.

Reference: The Pennsylvania Game Commission.

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