Guide

Look closerMammals

Weasels in winter white and their tracks in snow

December to February

Short-tailed weasels, also called ermine, swap their brown coat for white in late fall and keep only a black tail tip through winter. Long-tailed weasels, the more common weasel in Massachusetts, can turn white too, though fewer do so farther south: in Pennsylvania only about one in six long-tailed weasels turns white.

Why this time of year

The fall molt is set by shortening days, not by temperature, and in Pennsylvania it is usually finished by late November or early December. From December through February a weasel is in its winter coat, and fresh snow records the bounding trails these mostly hidden hunters leave. By late February or March the spring molt back to brown begins.

How to notice it

  1. The morning after a fresh snowfall, walk a brushy field edge, a woodland edge, or a stream bank and scan the snow for a line of small paired prints, two side by side, with a gap of open snow before the next pair.
  2. Look for the trail to zigzag or vanish into a small hole: weasels hunt mice and voles by scent, zigzagging back and forth and checking every hole and cranny.
  3. If a small white animal with a black-tipped tail darts past, stand still and watch from where you are; weasels often stop to stand on their back legs and look around.
  4. Enjoy the trail where you find it or follow it backward to where the animal came from; do not track it toward a den, and do not reach into stone walls, brush piles, or holes.

Try this with kids: Find a trail of paired prints in the snow and count the hops you can see from where you stand. Then step back and keep your hands in your pockets.

Word to know: “Molt”: shedding one coat of fur and growing another.

Safety

  • Watch weasels from a distance; never corner, chase, or try to touch one.
  • Do not follow tracks to a den or resting spot; winter food is scarce and a disturbed animal burns energy it needs.
  • Keep hands out of stone walls, brush piles, and burrows; look, do not reach.

Sources

  • massaudubon.orgMass Audubon Massachusetts December Outdoor Almanac: 'Long-tailed and Short-tailed Weasels molt from brown to white in the fall. In winters with little snow cover, their white pelage makes them easy to see if they are out and about in the daytime.'
  • pa.govPennsylvania Game Commission. Ermine fall molt 'begins in October and is usually complete by late November or early December'; spring molt mid-March to late April; 'The molts are triggered not by temperature but by amount of light per day'; in Pennsylvania 'perhaps one in six long-tailed weasels turn white'; black-tipped tail on both species; ermine gait a series of short bounds.
  • harwichconservationtrust.orgHarwich Conservation Trust, attributing notes to MA Division of Fisheries and Wildlife: winter coat white with black tipped tail; 'Long-tailed weasels are more common than ermines in Massachusetts'; habitats.
  • massaudubon.orgMass Audubon: weasel family are bounders whose rear paws land on or near the front paw spots (paired prints); 'It's best not to track animals back to their dens or bedding sites'.
  • nps.govNPS Northeast Temperate Network: short-tailed weasels turn white for snowy months; black tail tip kept year-round.
  • northernwoodlands.orgNorthern Woodlands: color change triggered by length of daylight, not temperature; white replaces brown over three to five weeks.
  • northernwoodlands.orgNorthern Woodlands: molts triggered by photoperiod; mid-Atlantic weasel populations already include both white and winter-brown animals.

Checked against these sources on November 3, 2026.

In the guide for December, January, February

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