On the Trail of Mustelids

Notes from a Tracker’s Journal

Like the excitement and energy of the arrival of spring, my last few weeks have been a month full of experiences with mustelids.  Also known as the weasel family (Mustelidae), they are represented by a variety of species in North America such as the long-tailed weasel, river otter, fisher, and wolverine. Mustelids have been one of my favorite groups of creatures to study, trail, and observe. With their slinky, elongated bodies and their high level of energy, these cunning beings are some of the most effective predators around.

From observing both a river otter and mink out at one of my favorite tracking spots, to seeing updates about fisher reintroduction plans in Washington State and reading about the capture and radio-collaring of a wolverine in the North Cascades, this month has inspired me to reflect upon the mustelid tracking I have done over the last decade. Below I have assembled a few of my photos and notes on a couple mustelids that I hope you find as interesting as I do! Happy tracking.

Fisher (Martes pennanti)

Fishers are a fairly large member of the weasel family, about the size of an elongated house cat, which spends most of their time hunting in the forests. They are very curious and energetic, and have been known to chase down squirrels in the trees.

Fishers historically inhabited Washington State until they were over-harvested during the turn of the century.  They are currently listed as an endangered species here in Washington, as no breeding population is known to exist.  A very small number of sightings have occurred along the Canadian border over the last twenty years.

Through my work as a wildlife biologist, I found out that a body of a wild fisher was discovered near Mount Rainier in 1990 and confirmed by the University of Washington.  Is it possible for a dispersing young adult to travel all the way from Canada to Mount Rainier? Or is there a small, undocumented population in the Cascades?  Sounds like a good tracking mystery to me.

Reintroduction efforts will be commencing in the fall of 2006 in the Olympic National Forest.  I feel very fortunate to have had the opportunity to spend a significant amount of time trailing fishers in Massachusetts, where they are abundant. The track photo below illustrates many of the key features of a mustelid footprint, including five toes, claws, and a c-shaped heel pad.

mustelids tracking

Mink (Mustela vison)

Mink are medium sized weasels, similar in size to a ferret you would find in a pet store. They spend most of their time hunting along the edge of water. As with most of the weasel family they are also very curious and energetic, and are quite adept at swimming.

I find their tracks along ponds, creeks, and wetlands all over the Puget Sound region and beyond. Mink eat a lot of crayfish and frogs and I often find their scats on top of rocks that are underneath overhangs, near the edge of a body of water.  It’s an interesting placement choice that probably has to do with making sure its scat is in a spot that stands out to other mink, possibly to communicate territory ownership.

In Washington State, mink are considered a priority species because of their value as a fur-bearer. Priority species are wildlife species requiring protective measures and/or management guidelines to ensure their perpetuation. Mink, marten, fisher, and wolverine are the mustelids that are priority species in Washington State.

Here are a couple photos from the mink encounter I had last month. The brave individual pictured below calmly watched me while it basked in the sun, cleaned itself, drank water, and explored the river bank. The track photo includes both a front and rear footprint.

mustelids tracking


Jason Knight is a former wildlife biologist with Wetland Resources and former instructor at Wilderness Awareness School. He now runs Alderleaf Wilderness College in western Washington.