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Mink Wildlife Note

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One of Pennsylvania’s most efficient predators, mink (Mustela vison) are semi-aquatic members of the weasel family (Mustelidae). Other mustelids include weasels, martens, fishers, wolverines, badgers, skunks and otters. Mink are found throughout most of the northern hemisphere in both Europe and North America. They live on the edges of lakes, streams and rivers. Adult males average two feet in length, including an 8-inch tail. They weigh 1½ to two pounds. Females are 10 to 15 percent smaller than males and up to half a pound lighter. Body configuration resembles that of a weasel: short legs; long, bushy tail; long, sinuous neck and body; short head; and pointed muzzle. A mink’s coat is thick, full and soft. A short, tight layer of underfur is covered with longer guard hairs, which give the pelt its luster. Colors range from russet to a deep, chocolate brown. Unlike some weasels, the mink does not turn white in winter.

Mink have excellent hearing and sight, and a good sense of smell. They rely on sight when foraging. A mink’s vision is clearer out of water than underwater. Acute hearing is also used to detect prey when foraging. Mink are able to hear ultrasonic vocalizations emitted by rodent prey. On land, they travel at a slow, arch-backed walk or a bounding lope, which they can keep up for miles. They swim and dive with ease; a webbing of stiff hairs between the toes of their hind feet helps propel them through water. Mink are most active at night and early morning, although they sometimes venture out during the day.

Active year-round, mink may curl up and sleep for several days during winter cold spells. Like most mustelids, they are agile and fierce fighters, killing prey with a hard bite to the back of the skull. Mice, voles and muskrats rank as most important foods of mink during all seasons.  Other prey include rabbits, shrews, fish, frogs, crayfish, insects, snakes, waterfowl and other birds, eggs, domestic poultry, earthworms and snails. Generally, a mink is an opportunist, feeding on whatever is most easily caught or found. Thus, it might avoid fighting to kill a healthy adult muskrat if crayfish were abundant and easily captured. Mink occasionally kill more than they can eat. In winter, they cache carcasses and revisit them to feed.

Mink den in abandoned woodchuck tunnels, hollow logs, vacant muskrat lodges, holes in stone piles and beneath large tree roots. Dens are usually near water and may have more than one entrance. Mink line their nests with dried grass, leaves and feathers; bones and scraps of kills often litter the nest area.

Mink are basically solitary, except during mating season, when they use a powerful scent from their anal glands to attract mates. Males fight over receptive females and are believed to mate with several females. Mating occurs from February to April, with most activity in March. After mating, the fertilized eggs develop slightly, then 13 to 50 days may pass before the embryos attach to the female’s uterine wall and continue developing. This is called delayed implantation and is common among mustelids. Females give birth in early May following a gestation period of 28 to 30 days after embryo implantation. Thus, total time from mating to birth may be 40 to 80 days.

At birth, young are 3½ inches in length, blind and hairless, and they weigh only a fifth of an ounce. Litters include two to seven young, with an average of four. In two weeks, young are furred; their eyes open after five weeks; and after six or seven weeks they are out foraging with their mother and learning how to hunt. The family disperses by late summer. Mink are sexually mature at 10 months.

Mink are best suited for areas that hold the greatest concentrations and varieties of prey. A male covers a range up to three miles in diameter, while a female’s range is much less. Individual home ranges overlap. There is very weak evidence that mink are territorial. The same den may be used by several animals in succession. One mink may have several dens along its hunting route.

Mink are extremely sensitive to environmental pollutants. At the top of the food chain in aquatic environments, they accumulate many chemical compounds and heavy metals in their tissue including polychlorinated biphenyls and mercury. Mink are often used as bioindicators of pollution in aquatic systems.

Mink live up to 10 years in captivity, and a wild one would be fortunate to survive two or three winters. Disease, road accidents, and regulated harvest are mortality factors. Mink are preyed on by foxes, bobcats and great horned owls.