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.