Montana Field Guide

Long-tailed Weasel - Mustela frenata

Largest and most widely distributed of the three Northern American weasels. Distinguished by its long, slender body and long neck. Longest tail of the North American weasels. During summer fur rich brown on the back and sides with yellowish-white under-parts, black tip on tail, and no whitish line down inside of leg. Acquires a white winter coat. Adult males noticeably larger than females. Total length: 11 to 16.5 inches. Weight: three to 12 ounces.

Short-tail weasel - white line down inside of leg, smaller. least weasel - no black tip on tail, smaller. mink - nearly uniform dark brown. marten - heavier, much larger.

Montana Range

Non-migratory.

Found in almost all land habitats near water. Has the broadest ecological and geographical range of the North American weasels. Prefers areas with abundant prey. Avoids dense forest, most abundant in late seral ecotones. Primarily nocturnal, but sometimes active during the day. Quite fearless and curious. Mainly terrestrial but can climb and swim well. Nests in old burrows of other animals (FWP). Occupies a diverse range of habitats. More prone to open country and forest openings than M. erminea. Common in intermontane valleys and open foresets where M. erminea is absent. May occur up to alpine tundra (Hoffmann and Pattie 1968).

More of a generalist than the short-tailed and least weasels. Feeds mostly on small mammals up to rabbit-sized, but eats birds and other animals as well (FWP). Males: rabbits, tree squirrels, and ground squirrels. Females: mice & chipmunks. Dietary componenets overlap. Both sexes will occasionally use birds, herptiles, and insects. (Jones et al. 1983).

Weasels will cache prey. This permits food storage without obesity, facilitating ability to pursue prey in narrow bur- rows. Males about 10-15% larger than females (Svendsen 1982).

Mates during summer, 205- to 337-day gestation; delayed implantation; young born during April; litter size four to nine.