They are hard to see against a backdrop of fresh snow, except for the large, dark black eyes, and the black tip at the end of their tail.
The long, thin bodies of weasels are a great adaptation for hunting rodents in their burrows, but they are a disadvantage in the winter climate because thin cylindrical bodies lose heat much faster than more spherical-shaped ones do.
Weasels usually retreat to a burrow, perhaps of some animal they have recently eaten, when they are not active, and they will often cache extra food there to tide them over on days when prey are scarce.
What determines when weasels molt into their white fur? It’s thought that declining hours of daylight in the fall are the primary cue, just as it is for migratory birds to begin their preparation to fly south. Molting from brown to white fur coat takes about three weeks, but a drop in temperature can hasten the molt, and unseasonably warm fall weather can slow it. Usually the molt to the all-white ermine phase is completed just about the time of the first snowfall, so the animal is perfectly camouflaged.
While walking along the bank of the Minnesota River south of Lac Qui Parle, we spotted a slender brown mammal scurrying between the large rocks and foliage.
But which weasel is it? According to the “ecology center“, of the three possibilities that it could be in North America, this one is most likely a Short-tailed Weasel, otherwise known as the Stoat in Europe and Asia.
Short-tailed Weasels are relatively recent immigrants to the Americas, arriving during a period when there was an ice-free land bridge between North American and Asia about 2 million years ago. Since then they have spread throughout all of the Americas, even down to the tip of South America.
Prior to that time, about 5-7 million years ago when northern temperate forests were slowly being replaced by temperate grasslands, a weasel ancestor crossed another land bridge between the continents, giving rise to the Stoat of Eurasia on that continent, and a look-alike Long-tailed Weasel in North America. Other than their body size differences, the two species are remarkably alike in looks and behavior. And both molt their brown fur to pure white in the winter in north temperate climates, making them almost undetectable in snow.