An online resource based on the award-winning nature guide

Weasel Family

Mink and Fisher Tracks

1-16-19 fisher and mink tracks img_2238As members of the weasel family (Mustelidae), Fishers and Mink have five toes on both front and back feet. Often all five digits do not register, but in prime tracking snow, you can sometimes see them. Typically, mink tracks are found near a body of water, and fisher tracks are found under a canopy, not in the open. Where you have both water and trees, it’s possible to see signs of both animals.

In general, the larger the animal, the larger its tracks. Mink weigh one to three pounds; fishers four to eighteen pounds. In this photograph, the mink tracks (smaller, in the middle) are heading towards the top of the photograph, and the fisher tracks (top most and bottom most) are heading towards the bottom of the photograph. They were both traveling on a frozen woodland stream.

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Distinguishing Small Weasels

12-21-18 ermine_U1A8001New 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.)

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North American River Otters Foraging For Fish

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Whether or not North American River Otters made the original holes evident in Wednesday’s Mystery Photo, they were responsible for keeping them open by frequently poking their heads up through them for some air. Congratulations to Noel K. for being the first to correctly identify their surface holes.  This was a tricky Mystery Photo, as there were none of the usual signs of otter activity (tracks, fish remains, etc.) on the ice surrounding the holes.  This is probably because the ice was too thin to support the weight of an otter.  To find the most humorous response, scroll down on Wednesday’s Mystery Photo comments until you get to Peg Emerson’s.

These semiaquatic members of the weasel family are active year-round and while they are mainly nocturnal and crepuscular during the summer, they are frequently spotted during the day in winter.  If otters encounter open water, they rarely resist the urge to enter it and pursue resident fish.

Thanks to their webbed feet and streamlined body, otters are accomplished swimmers and divers. They are able to reach a depth of around five feet and remain submerged for up to four minutes as they hunt underwater. Top swimming speed is seven miles per hour. (They can achieve a speed of up to 18 miles per hour when running and sliding on snow or ice.)  While fish are their mainstay, these carnivores also consume frogs, snakes, turtles, insects, birds and bird eggs and the occasional mammal (mainly muskrat).  Though called “river” otters, they forage in fresh, salt and brackish waters. (Thanks to Rita and Dave Boynton for photo op.)

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A True Mystery Photo

11-2-18 flying squirrel tails_U1A1190A discovery recently brought to my attention has stumped this naturalist.   What you are looking at is a collection of Flying Squirrel tails lying within a 30-square-foot patch of ground adjacent to a stand of Eastern Hemlocks. For several days in succession, additional tails appeared each morning, eventually totaling 20 or more.

Flying Squirrels, both Northern and Southern, are part of many animals’ diet.  Among the documented predators are Great Horned Owls, Barred Owls, Screech Owls, Northern Goshawks, Red-tailed Hawks, Martens, River Otters, Weasels, Fishers, Red Foxes and Bobcat.  Many of these animals can gain access to the trees where the Flying Squirrels reside.  Others take advantage of squirrels foraging on the ground.

The puzzling part of this mystery is the large number of tails.  In cold weather (usually in winter, but we’ve had below-freezing nights recently), Flying Squirrels huddle together in tree cavities in an attempt to provide themselves with added warmth.  Did a foraging Fisher discover a communal den?  How did it manage to capture so many squirrels?  Did the survivors remain in the same cavity, only to be captured in subsequent nights?  So many questions that this naturalist cannot answer. Perhaps a reader can! (Thanks to John Quimby and Michael O’Donnell, who kindly shared their fascinating discovery with me.)

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Fisher Landing

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Although capable of climbing trees, Fishers spend most of their time on the ground under dense woodland canopy. In the winter Fishers constantly leave sign while traveling two to three miles a day in search of squirrels, shrews, mice, voles, porcupines, hares and grouse, among other things, to eat. Beds at the base of trees, small saplings bitten, rubbed and rolled on, scat and urine marking – all are quite commonly encountered when following Fisher tracks. The Fisher sign I find quite elusive and therefore very rewarding to come upon is the imprint they make when they land in the snow after jumping down from a tree they’ve climbed. (Photo: landing imprint)

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Mink Exploring Streams

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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.

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River Otter Tails

3-31-17 otter tail impression2 026From their nose to the tip of their tail, North American River Otters measure three to four feet long. Their tail makes up anywhere from a third to nearly a half of their length. A River Otter’s tail is very thick at its base, packed with muscles, flexible, and tapers to a point. It is used to steer when an otter is swimming slowly, propel the otter when it is swimming at high speed and to help the otter balance when it stands upright on its hind legs. River Otters, known for their powerful swimming, can reach speeds of six to seven miles per hour with the help of this appendage.

When loping through the snow, River Otters often hold their tails up off the surface of the snow, but not always. Occasionally drag marks can be seen.  In the accompanying photograph, an otter had leapt up an incline, and in so doing left an imprint of its impressive tail in the snow.

(Thanks to Alfred Balch for photo op, and Joan Waltermire for her sharp eyes.)

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