American Ermine

The American ermine has a body plan typical of weasels. It has short legs, a long body and neck, and a small triangular head with short round ears. It has a brown dorsum with a white venter (except during winter when the coat is fully white) and a short, black-tipped tail. The black coloring of the tail may serve to distract predators and divert attacks away from the body, which blends in more with its surroundings. American ermines are sexually dimorphic and males are 30% larger than females.

The species is found throughout most of North America aside from most of Alaska (although it is found on some islands in southeastern Alaska), eastern Yukon, most of Arctic Canada, and Greenland, where it is replaced by M. erminea. It reaches the northern extent of its range in Ellesmere Island and a portion of eastern mainland Nunavut and ranges from here to cover almost all of western North America south to northern New Mexico, and eastern North America south to northern Virginia. It is absent from most of the Southeastern United States and the Great Plains.

Ermines are primarily nocturnal hunters, although they can also be seen frequently during the day. In North America, where the ecological niche for rat- and rabbit-sized prey is taken by the larger long-tailed weasel (Neogale frenata), the carnivorous American ermine preys mainly on mice and voles. Shrews, young cottontails, chipmunks, deer mice, jumping mice, and house mice are also preyed on. Occasionally, small birds, frogs, small fish, and earthworms are eaten. Usually the ermine kills by biting at base of skull.