If the river otter is the most aquatic member of the mustelid family, and weasels represent the terrestrial branch of the clan, the American mink is the adept middle child, taking advantage of its adaptations both in the water and on land to make a living.
Like both otters and weasels, mink have long, sleek bodies, the sharp teeth of a predator, and small – but keen – ears and eyes. Their fur – long a fashion staple – is a combination of oily guard hairs, which afford some water-repellency, and an undercoat that grows thick in winter to provide warmth. It’s a common makeup in winter-active mammals – and a bit like us humans wearing a waterproof Gore-Tex shell over layers of insulating polypro or wool.
With partially-webbed feet, mink are good swimmers, although not as skillful as otters. Unlike their more aquatic cousins who can see underwater and stay submerged for long periods, mink tend to locate food from outside the water before diving in to catch it, mainly by feel, and resurfacing relatively quickly.
Mink are also good land hunters, using their size and stealth to catch prey. At an average weight of two to three pounds and measuring about 22 inches long – including a tail that makes up about a third of that length – mink keep a low profile and are able to slip into narrow openings to pursue prey.
With a range that extends across North America, mink diets vary depending on where they live, although they always live near the water – whether it’s along a stream, near a pond or marsh, or by the coast.
“Mink are successful because they are generalists,” said Paul Hapeman, a biology professor at Central Connecticut State University. “That’s the beauty of the mink: it can take advantage of both the food resources and denning options wherever it is.”
On the salt flats of Florida, where Hapeman has studied the animals, mink live in the intertidal zone and estuaries, more marine environment than terrestrial. Their diet there consists primarily of crustaceans, with a few fish and small shorebirds thrown into the mix. In the prairie pothole region of the northern Great Plains, conversely, where mink live in shallow wetlands, their diet consists largely of waterfowl.
In the Northeast, mink change their dining habits with the seasons. And because they can hunt both in the water and on land, their options remain relatively open through the year.
“Mink are opportunistic,” said Dave Erler, senior naturalist at Squam Lakes Natural Science Center in Holderness, New Hampshire. “They’ll grab a red squirrel, crayfish, they can still catch mice (in winter), and they will take birds.”
Muskrats are a preferred food source, especially those that occupy the fringes of prime muskrat habitat, along the edges of wetlands where mink tend to travel. This segment of the population is often weaker, less established, and less protected, which makes them more vulnerable to predators.
“Mink can surprise a muskrat either in its den or when it’s feeding near the water,” said Erler, noting that while large otters can’t access small openings to muskrat dens, mink can slip inside with relative ease.
As opportunistic in their denning sites as they are in sourcing their meals, mink sometimes take over the dens of muskrats, although they’ll hole up in a variety of denning options ranging from abandoned burrows and beaver lodges to tree root systems and rock piles.
They also tend to be transitory within their territories. Male mink maintain larger territories than females and will travel two to three miles, usually along stream beds and wetlands, to hunt and seek mates. Territories sometimes overlap, and a male mink will often have more than one potential mate within his range. Females also travel, and both sexes use multiple denning sites, which may also be used – at different times – by other mink.
The exception to this wandering is when female mink stay put to raise their young. Typically arriving in litters of about four, the babies are born in May, blind and bald. By six weeks of age, young mink are ready to accompany mom on foraging and hunting expeditions. They’re on their own by summer’s end, seeking out whatever the season and the habitat have to offer.
Meghan McCarthy McPhaul is an author and freelance writer. She lives in Franconia, New Hampshire. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine, and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation.