The mink (Mustela vison), belongs to the Mustelid family of weasel-like animals that possess well developed anal musk glands. The second part of its scientific name, “vison”, means “a scout”.
Mink are found throughout Canada and the United States, except in the tundra and desert regions. They are common throughout Ontario.
The mink has short legs, a long, weasel-like neck and trunk, and a small, sharply pointed face with small ears. A semi-aquatic mammal, the mink has dense, oily underfur for protection in the water, and stiff hairs between the hind toes to aid in swimming. Other adaptations include the defensive musk glands common to all mustelids, which give off an odour more offensive to most people at close range than that of the skunk. Sight, smell and hearing are all keen. The mink stands 8.9 to 12.7 cm (3.5 to 5 in) at the shoulder, and is 45.7 to 76.2 cm (18 to 30 in) long. The latter measurement includes the 20.3 cm (8 in) tail. The male weighs 0.6 to 1.3 kg (1.25 to 2.75 lbs), and the female, 0.5 to 1 kg (1.13 to 2.13 lbs). The mink does not undergo seasonal colour variation, but moults twice a year. The spring moult begins in March and April and ends in mid-July. The autumn moult begins in mid-August and, by October, the pelt is prime and the skin beneath the fur is creamy white. The mink’s fur is a uniform, rich, dark brown, except for a patch of white on the chin. It consists of long, coarse, outer guard hairs and dense, oily under fur. The immature mink is paler in colour than the adult, and has a thinner coat of guard hairs. Although colour phases do not occur in the wild, mink farmers can breed colour mutations. The pelt of the farmed mink, however, is not as hardy as the pelt of a mink that has lived under natural conditions.
Both sexes are capable of mating at ten months. Although they breed during their first year, some evidence suggests that first year males produce fewer pregnancies than do adults. The male and the female may take a number of mates during the mating season, which occurs between late February and early April. Mating persists through the three-week heat period, and the animals devote themselves to sexual activity and rest. The rough-and-tumble courtship that precedes copulation often results in bruises to the neck that can be seen on the leather side of the pelt. The gestation period is not as prolonged in mink as it is in fisher. It may last from 40 to 75 days, and the average time is 51 days. This variation results from delayed implantation of the egg. Litter size also varies widely. From two to ten kits may be born to one female. The average number is four. In April or May, the young are born in natal dens lined with grass, leaves, fur or feathers. The kits are naked except for short, fine, white hairs. Their eyes open after about 25 days, and weaning occurs within five or six weeks. By eight weeks, the kits have begun to capture their own prey. They grow rapidly, the females attaining their adult weight at four months and the males, at seven to ten months. The young remain within the family territory until late August. Many will die before the end of their first year. Those who survive may live from three to six years. The age of trapped males can be determined by the size and weight of the baculum, or penis bone. On a cased skin, the presence of a scar at the penis level indicates that the mink was male. Immature females can be distinguished from adult females by the teats, which are small and colourless in the young and dark and raised in the adults.
Mink prefer areas in which there are water bodies such as streams, lakes or ponds, and avoid open areas. Forested, log-strewn or thicketed areas offer prime habitat. Den sites are usually dominated by coniferous trees such as spruce, balsam and cedar. The entrances are normally found in dense shrub layers. Dens may be made by the mink or taken over from other animals. They are usually within burrows that are 2m to 4m (about 8 to 12 ft) long, 10 to 15 cm (about 4 to 6 in) in diameter, and 0.3 to 1 m (1 to 3 ft) below ground. Burrows are frequently located along or near the banks of water bodies, under logs or stumps, or within recesses in rocks.
Food and Feeding Behaviour
The mink will eat almost any living thing that it is capable of overpowering. Often, it preys on larger animals. In its diet are fish, crayfish, clams, earthworms, insects, mice, frogs, muskrat, moles, rabbits and birds. Several species of waterfowl are eaten. In marshes, the mink prey on muskrat. The effect of mink on muskrat numbers has not been determined, but heavy predation is taken to be a sign of muskrat over-population. There is no need to remove the predatory mink to save the muskrat population, since the surplus muskrats would only die of other causes. The mink hunts by consistently exploring holes in logs, stumps and shoreline tangles along its travel route on each trip. It kills by biting its prey through the neck at the base of the skull. Extra food is cached for later use.
Mink are usually solitary, nocturnal animals that can be seen hunting at dawn and dusk. They are active all year, but may retreat to dens during cold and stormy weather. Males use a variety of dens, but females keep to one or two during the winter months. Families use a number of dens before the young disperse. Mink will willingly swim under water, and can dive to depths of 4.5 to 5.5 m (about 15 to 18 ft). Although the mink can travel long distances, the female maintains a home range of less than 3 square km (1 square mi), and the male, of 5 to 8 square km (about 2 to 3 square mi). Juveniles travel more widely, covering from 3 to 45 km (about 2 to 28 mi) in their search for territories. The home range of the immature male is 8 square km (about 3 square mi), and the young female’s is 5 square km (about 2 square mi). In one night’s hunt, however, an animal rarely travels more than 300 m (984 ft) from its current den. Territories are marked by scent posts situated in prominent places such as on mossy hummocks, rocks, stumps or fallen logs in comparatively sheltered spots close to the dens. The scent glands also emit a foul liquid when the mink is excited, irritated or injured.
In areas dominated by a single prey species, the mink population follows the fluctuations experienced by the prey population. Cottage development can also reduce mink numbers, since it diminishes the forested habitat along shorelines. In autumn, there are usually from two to five mink within areas of 2.6 square km (1 square mi) where habitat is favourable. Several parasites are present in mink, but their precise impact on the population is unclear. The giant kidney worm and the Guinea worm found beneath the skin, and a type of tapeworm that causes cysts in the neck muscles and thoracic cavity are all common. External parasites include fleas, ticks, and lice. None of these parasites adversely affect mink under normal conditions. Other diseases such as tularemia are present elsewhere in mink, but are not known to be a problem in Ontario.
Mink are not usually harvested on the basis of quotas, but quotas can be set in some instances. Trappers should consult the summary of trapping regulations to determine the season for mink in their areas. It is often desirable to reduce the trapping pressure on breeding females. Many males are caught further from water while females are usually caught closer to their dens. Therefore, it is possible to harvest selectively, especially if live-traps are used. This approach may be called for in some areas. Nuisance mink must sometimes be removed from sites such as hatcheries and private fishing ponds. Trappers should assist landowners who are experiencing problems with mink predation. On the whole, however, the impact of mink on fish populations is not significant.