Montana Field Guide

Short-tailed Weasel - Mustela erminea

Of the three North American weasels is intermediate in size and one of the smallest carnivores in the world. Males distinctly larger than females. During summer fur is dark brown with white under-parts, white feet, and white line down hind legs. Molts to white during winter, except black tip on tail. Total length: seven to 13 inches. Weight: one to six ounces.

Long-tail weasel - larger, tail longer. least weasel - smaller, short tail, no black tip on tail. mink - larger, uniform color.

Montana Range

Non-migratory.

Inhabits brushy or wooded areas, usually not far from water. Tends to avoid dense forests. Prefers areas with high densities of small mammals. Most abundant in ecotones. Mostly nocturnal but will hunt during the day. Active throughout the year. Dens in ground burrows, under stumps, rock piles, or old buildings (FWP). In Montana apparently prone to montane forest associations. Elsewhere occupies a diverse range of habitats. Nests in hollow trees, rock piles or burrows.

Weasels prey on a variety of small mammals and birds, they specialize in hunting voles (FWP). Mostly small warm-blooded vertebrates, primarily cricetidae. Hunts under snow in winter. Females generally eat smaller prey. May use invertebrates. Ermine will kill larger prey-- e.g. rabbits.

As in many mustelids 2 degrees sexual dimorphism is pro- nounced--males 30% larger than females. Local distribution & densities probably tied to prey availability. Well adapted to snowy environments.

Breeds during summer; 8.5- to 10-month gestation; delayed implantation; young born April or May; one litter per year of four to 13 young (FWP). Induced ovulation. 8.5-9 months delay of implantation. Gestation 9.5-10 months. Females first breed at 2.5 months. Males at 14 months. Breed Jun-Jul, give birth in Apr-May.