New England has two small weasels: Long-tailed and Short-tailed. Both of these predators molt twice a year, from brown to white in the fall, and white to brown in the spring. The name “Ermine” can refer to either of these two species, but it is most commonly used when referring to the Short-tailed Weasel.
Telling the two species apart can be challenging. Long-tailed Weasels are the larger of the two (head to tail = 12-14 inches), while Ermine are slightly smaller (head to tail = 7-13 inches). Unless you have both species in front of you, however, their size is hard to assess. A more helpful distinguishing characteristic is the length of their tail relative to their body length. Long-tailed Weasels have a tail longer than half their body length with a black tip. Ermine have a tail length which is around a third of their body length — it also has a black tip. (Photo: Ermine (Short-tailed Weasel). Thanks to Sharon and Chad Tribou for photo op.)
The pattern of diagonally-paired tracks indicates that it’s likely that a member of the weasel family has been travelling on top of this mostly-frozen stream. The presence of water makes it likely that a Mink made them. For the most part, Mink are restricted to forest cover and ponds, streams and rivers. When bounding, their hind feet register almost exactly where their front feet were, creating this double-print pattern.
Many members of the weasel family, including Long-Weasels, Ermine (Short-tailed Weasels), and Fishers, also make these paired tracks, especially in deep snow. Size is one way to discriminate between them, with the size of Mink tracks (1 ½”-long) falling in between 3″- long Fisher tracks and 1”- long weasel tracks.