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December Nature Notes: Least Weasel

Decreasing daylight hours responsible for change in fur color.
With the decreasing daylight of autumn, the least weasel (Mustela nivalis) stops producing hormones for pigmentation of its fur, and a snowy white winter pelage grows in to replace the earthen brown summer coat. The feet and belly remain white year-round.

The sinuous predator weighs 2 ounces, its slender body having a diameter of about 1 inch. Like other weasels, its short, stubby legs give it a bounding gait. Five toes on each foot are fully furred.

Truly ferocious, America’s tiniest carnivore eats primarily white-footed mice and meadow voles, chasing them along their runways, pouncing on them with reckless abandon, and swiftly killing them with repeated bites to the throat, nape and head. Insects are added to its diet in summer.

Active both day and night to maintain a constant body temperature despite rapid heat loss due to its small size and shape, the least weasel rests for short inactive periods in an underground burrow it has purloined from one of its victims, lining its nest with trophies of the fur of its prey to insulate it.

The least weasel reaches the southern limit of its range in north-central Illinois and the Appalachian mountains of North Carolina. Known predators include foxes, cats, hawks and owls.        

Carol McFeeters Thompson is a regular contributor to OutdoorIllinois and the site interpreter at Weldon Springs State Recreation Area


By: Carol McFeeters Thompson