Ferrets, weasels, and stoats, also called ermines, are members of the Mustelid family. They're closely related to each other as well as to martins, minks, wolverines and otters. Mustelids probably evolved from a carnivore called a miacid during the early tertiary period, about 65 million years ago. Ferrets, stoats and weasels are all long-bodied hunters that live in the temperate latitudes throughout the world. In the tropics the place of mustelids is taken by civets, genets and mongoose.
Black footed ferrets are larger than both stoats and weasels. The ferret can also be distinguished from the others by a black mask, feet and tip of the tail. In summer the coats of stoats and weasels are brown on top with white or yellow bellies. A ferret is 14 to 18 inches long and weighs 1 1/2 to 2 1/2 lb. Males are larger than the females. A male long tailed weasel is from 9 to 11 1/2 inches long, and weighs from 4 5/8 to 10 oz. Females are 7 to 9 inches long and weigh from 3 to 4 oz. The weasel's tail is more than half the head and body length. Male stoats are 6 to 9 inches long and weigh 2 1/2 to 6 oz., while the females are 5 to 8 inches long and weigh 1 1/2 to 2 1/2 oz. The stoat’s tail is not as long as the weasel’s and longer than a ferret’s.
The stoat is active for short periods all day and night, with the active periods interrupted by three- to five-hour naps. The weasel is active both day and night and hunts for prey on the ground, in trees and in underground burrows. The black footed ferret lives around prairie dog towns and catches the prey outside its burrow entrance. The ferret almost went extinct when prairie dog towns were eradicated to make room for human habitation; it is still considered endangered.
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The long tailed weasel’s North American range is from Western Canada into the United States. It lives in open areas of forests, meadows and fields near water. Despite its wide range it’s considered uncommon. The black footed ferret has been reintroduced into northeast Montana, western South Dakota and southeast Wyoming. It will sometimes take over the burrow of its prey if it can. The stoat’s habitat is coniferous forests or mixed conifer hardwood forests, brushy fields, tundra, hedgerows and dense vegetation around swamps and marshes from Alaska, Canada, the western United States into California and New Mexico, the northeast and the northern Midwest. It will take over the burrow of a chipmunk or another small mammal and line the nest with the prey’s fur or feathers. The stoat can have different nests in different parts of its territory. Unlike the weasel and the ferret, the stoat is considered common.
The weasel’s nest is a burrow or rock or brush pile. It breeds in the summer, but the young aren’t born until the following spring. The stoat also mates in summer, but like the long tailed weasel, the development of the embryos is delayed and the babies aren’t born until the next spring. Unlike the weasel and the stoat, the ferret doesn’t have delayed development. It breeds in early spring and a litter of one to five or more is born in May.
The weasel eats small and medium-sized mammals like mice, voles and pocket gophers, young rabbits, birds and their eggs, snakes, insects and carrion. The stoat eats small rodents and insects and sometimes kills prey larger than itself. The ferret eats prairie dogs and other animals that live in prairie dog towns.