Least Weasel

Mustela nivalis. By Dennis C. Joyes

This story is featured in Montana Outdoors July-August 2015 issue

According to Blackfoot legend, the weasel is the bravest of animals, a hunter bold out of all proportion to his size. Modern scientists agree, as every feature of these graceful and lightning-fast little animals seems designed to make them the perfect predator. This is especially true of the least weasel, the smallest of three weasels found in Montana and the world’s smallest carnivore.

The German word for the least weasel, mauswiesel, refers to its tiny size. Males are no more than 7 inches long, including the tail, and females rarely exceed 5 inches. Both sexes are brown above with white underparts, coloration similar to that of Montana’s two other weasels, the short-tailed and long-tailed (the latter with cream underparts). Unlike its cousins, the least lacks a black tail tip.

In winter the coat of the least weasel turns entirely white. Though soft, the fur lacks the silky elegance of the short-tailed weasel, or ermine, whose coat was coveted by Native Americans and European royalty.

All weasels have long, slender bodies, short legs, and a pointed, rather flat head with short ears, catlike whiskers, and large black eyes. Its neck is long, allowing the weasel to snatch prey from tight spaces. The head is its largest part, so a weasel can enter any hole its head fits into. Weasels appear almost boneless and are so flexible that they can reverse directions in impossibly small spaces. The jaws are short, heavily muscled, and armed with 34 razor-sharp teeth.

The least weasel is distributed across the northern part of continents around the world. In North America, the species occurs across Canada and down into Montana, the Dakotas, the Midwest, and even as far south as Kansas. In Montana they are found everywhere except in a few counties bordering Idaho, with most reports coming from northeastern counties.

Least weasels live in grasslands and open woodlands and along field edges and fencerows, wherever they can find abundant prey. They coexist with their larger cousins as long as prey is abundant.

Food and Hunting
Dubbed a “hair-trigger mousetrap with teeth” by one biologist, the least weasel is a specialized predator whose diet is mainly mice and small voles. It eats insects and ground-nesting birds, but only if other prey is scarce.

Least weasels are solitary predators that hunt with fierce concentration, checking every nook and cranny and frequently standing upright to survey their territory. The tiny carnivores search for prey under snow and often follow tunnels made by mice and voles. They instinctively attack moving prey, which they dispatch with a quick bite through the back of the neck. Because of their high energy demands, weasels hunt both day and night, consume about half their body weight daily, and stockpile prey during times of abundance.

“Unlike the short- and long-tailed weasels, the least weasel does not delay implantation [of the embryo],” writes Kerry Foresman in Mammals of Montana. “Breeding may occur throughout the year, even during the coldest months of winter.” Gestation takes 34 to 37 days. In a nest made in an abandoned chipmunk or vole burrow—the inhabitants of which may have found themselves on the weasel’s dinner menu—the female gives birth to four or five young. The male disappears after mating, so the female is left to both care for the pups, born blind and helpless, and hunt for food. Weasel kits eat voraciously, grow rapidly, and are able to kill small mice within seven weeks. They are fully grown in 12 to 15 weeks, after which families break up and the young set up territories of their own.

Conservation status
Least weasels are seldom seen and thus considered relatively rare. Their numbers vary with prey abundance, and they, in turn, are vulnerable to a variety of predators, including domestic cats and dogs. The species is not considered threatened and will likely thrive as long as there is abundant habitat for mice and voles.Bear bullet

Writer Dennis C. Joyes lives in Ontario and frequently visits his home state of Montana.