Illinois Natural History Survey - University of Illinois


Susan Post


During a late February evening I was driving to a frog monitoring class. As I wound my way through the local forest preserve, my mind was wondering when it would be warm enough to hear frog calls? Suddenly a dark shape bound in front of the car, hurrying from snow bank to snow bank—a mink!  Wow, a wildlife encounter beats a frog call any day! Why wasn’t it hibernating and what was it doing?  Time to pester one of my favorite Illinois Natural History Survey mammologists, Joe Merritt, author of The Biology of Small Mammals, to find out more about mink.

Jim Parnell

Photo by Jim Parnell

Minks (Mustela vison) are never found far from fresh water and occur throughout the United States, with the exception of the Southwest, which is too dry for their needs.  In Illinois they may be along the banks of drainage ditches and streams or the marshy shores of ponds and lakes where there is suitable cover and food resources. An abundance of minks is directly correlated with large populations of muskrats, upon which the mink prey.

As members of the weasel family—the Mustelidae—they are related to badgers, otters, and weasels. This family is the largest in the mammal order Carnivora. They share several characteristics with other weasels, including a flexible backbone, which permits them to arch their backs while bounding. They have small, flattened heads and short sturdy legs. They differ from other members of the genus Mustela (long-tail and least weasels), in Illinois, as minks are larger, have bushier tails, and longer hind feet. Their under and upper parts are nearly the same color, rather than white or white with an orange wash. Minks are found in aquatic habitats, and unlike weasels, minks do not turn white in the winter.

Minks, who are excellent swimmers, are specialized for an aquatic life and seldom wander far from water. Their toes are connected with webs at their bases. They have  bushy tails and small ears that barely project above their fur. Their water repellent fur is a dark chocolate brown and is lighter on the bottom than the top.

With poor eyesight and hearing, they must rely on their keen sense of smell to locate prey. Their prey includes muskrat, fish, cottontails, crayfish, waterfowl, amphibians and reptiles, and insects. Usually they feed and hunt at night. To subdue the prey they inflict a series of fatal bites to the neck and base of skull. Their diet varies, depending on the availability of food items at different times of the year. As minks are active year-round, they will cache prey for the winter. Minks are solitary except during the mating season and while the young are with the mother. Minks will mate from January to March, and due to delayed implantation of the embryo, young are not born until April or May. A litter consists of three to six hairless, pink kits (young). They quickly grow fur and their eyes will open in about three weeks. They will be weaned between 1.5 and 2 months, and by 10 months the kits are sexually mature.

Mink dens are usually near the water, and may be in hollow logs, under stumps or tree roots, in rock piles, or a burrow in the bank. The dens are located one to three feet below ground and have several entrances.

While great horned owls, foxes, coyotes, and bobcats will occasionally prey on minks, humans are their principal predators. Trapping takes its toll, but habitat destruction and drainage of wetlands are also factors.


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