Photo: NPS/Jim Peaco

White as Snow: Long-tailed Weasels in Winter

For most mammal-watchers in the Finger Lakes, the Long-tailed Weasel is among the last common species to check off one’s life list. It’s little wonder, as weasels are shy, usually silent, often underground, and most active at night. In winter, seeing them is all the more challenging, as they acquire camouflage as white as the frozen landscape. Typically, we observe no trace of their presence except their tracks in the snow.

But meanwhile, a rich, peculiar, and dynamic life history is unfolding out of our view.

Long-tailed Weasels have the largest range of any weasel in the Western Hemisphere, from the southern United States to southern Canada. In the northern part of their range, including our Finger Lakes region, Long-tailed Weasels overlap with Least Weasels (Mustela nivalis) and Short-tailed Weasels (M. erminea), but stand apart by their larger size (11–17 inches long) and proportionally longer tails. The size difference partially explains ecological niche separation, as the smaller weasels succeed better in pursuit of meadow voles and other comparatively puny prey. Long-tailed Weasels also exclude other weasel species by fighting them off, especially at the southern limits of the range overlap.

Long-tailed Weasels do not hibernate. In colder climes, including New York, they molt from brown coats with off-white undersides into pure white in winter, except for black tail tips. White pelage against a snowy backdrop helps the weasels to evade detection by both predators and prey. The dark tail tip helps to shift the aim of aerial hunters, such as hawks and owls, away from a weasel’s vital organs.

The timing and extent of winter molt appears to arise more from genetic predisposition than from physiological changes triggered by the weather, with more northerly populations turning white earlier, and more southerly populations keeping brown patches throughout the winter. Therefore, scientists speculate that reduced snow cover from climate change could leave our white winter weasels much more vulnerable to predation.

This white fur is short and relatively poor for insulation. Furthermore, because of their long spines, weasels cannot curl into a ball for heat retention as dogs and cats do. As a result, Long-tailed Weasels, even though they do spend much of the winter in moderate temperatures underground, must constantly generate body heat.

So they eat voraciously – up to a third of their body weight per day. Long-tailed Weasels strongly prefer rodents, shrews, moles, and small rabbits. When prey is abundant, Long-tailed Weasels kill more than they can immediately consume. They cache their surplus in burrows or sometimes even in trees.

They often hunt by lying in wait next to burrow entrances to ambush prey. They can also hunt underground, applying their keen hearing and sense of smell as well as formidable speed and maneuverability in tight spaces, chasing and cornering victims, then dispatching them with a bite that crushes the windpipe. Long-tailed Weasels sometimes even kill large rabbits and fowl in open spaces above ground by leaping on, grasping tenaciously with all four feet, and delivering lethal bites to the nape or skull.

Long-tailed Weasels are solitary, except during the breeding season from July through August. Males usually have multiple mates; females sometimes do as well. Copulation lasts 1 to 4 hours. Soon after fertilization, the female’s reproductive system goes dormant. Embryos do not implant until the following spring. Most development occurs during just the last month of gestation, and finally, a litter of 4-6 kits is born between mid-April and mid-May, just when prey is becoming most active and abundant again. With some understanding of their movements, we can readily find and identify the distinctive tracks of Long-tailed Weasels in winter. The weasels bound along, deftly placing their rear feet just where the front feet landed and lifted a moment before. Thus, they leave just one tidy pair of pawprints close together, then another pair onward after the next leap, and so on. Long-tailed Weasels can also confound trackers by doubling back, looping around, varying their stride length, dragging their tails, and/or disappearing into a burrow. Actually spotting a weasel at the end of the trail takes uncommon luck and patience. But the marks in the snow are their own reward – a revealing record of marvelous animal energy, agility, and adaptation.

This article by Mark Chao originally appeared in the Winter 2023-2024 issue of our quarterly print newsletter, The Land Steward.