Montana Field Guide

Least Weasel - Mustela nivalis

The smallest weasel and smallest carnivore in North America. Similar to other weasels in color and body form. Males are larger than females. Fur is brown above and whitish below during summer. Entirely white during winter. No black tip at end of short tail. Total length: less than 10 inches. Weight: one to three ounces.

Much smaller than the short- or long-tailed weasel. both short- and long- tailed weasels have black tip on tail.

Montana Range

Non-migratory.

Variety of habitats, including meadows, fields, brushy areas, and open woods. Avoids dense forest, prefers ecotones. Abundance of small mammals is important in determining the local distribution of least weasels (FWP). Marshy areas, meadows, cultivated fields, brushy areas and open woods (Svendsen 1982). Nest in shallow burrow about 5 inches underground (Jones et al. 1983).

Feeds almost entirely on mice. Small enough to pursue rodents into runways, burrows, and nest chambers (FWP). Small rodents (voles) & rabbits. Males twice as large as females, and are able to shift to the larger prey (rabbits and water voles). Smaller females are better able to exploit small rodent burrows (Svendsen 1982).

Size of home ranges may increase when small rodents are scarce. Pop. densities fluctuate in response to changes in small mammal abundances (Svendsen 1982).

Breeds year round; young born any time of the year; delayed implantation does not occur; litter size usually four to five (FWP). Both male & female reproductively mature at 3-4 months. Males may not breed until 10 months old. No delay of implan- tation. Gestation 35 days. Litter size 3-9. 2-3 litters/ year. Apparently breeds all year. (Svendsen 1982).