Mink are polygamous and males may fight ferociously for mates during the breeding season, which occurs from late January to late March. Gestation varies from 40 to 75 days with an average of 51 days. Like most other members of the weasel family, mink exhibit delayed implantation; the embryos do not implant and begin completing their development until approximately 30 days before birth.
The single annual litter of about 3 to 6 young is born in late April or early May and their eyes open at about 3 weeks of age. The young are born in a den which may be a bank burrow, a muskrat house, a hole under a log, or a rock crevice. The mink family stays together until late summer when the young disperse. Mink become sexually mature at about 10 months of age.
Mink usually occupy abandoned muskrat dens. However, mink also will use the burrows of ground squirrels and rabbits, as well as cavities available in brush and rock piles.
Mink are active mainly at night and are active year-round, except for brief intervals during periods of low temperature or heavy snow. Then they may hole up in a den for a day or more. Male mink have large home ranges and travel widely, sometimes covering many miles of shoreline. Females have smaller ranges and tend to be relatively sedentary during the breeding season.
Mink are shoreline dwellers and their one basic habitat requirement is a suitable permanent water area. This may be a stream, river, pond, marsh, swamp, or lake. Waters with good populations of fish, frogs, and aquatic invertebrates and with brushy or grassy ungrazed shorelines provide the best mink habitat. Mink use many den sites in the course of their travels and the availability of adequate den sites is a very important habitat consideration. These may be muskrat houses, bank burrows, holes, crevices, log jams, or abandoned beaver lodges.
The mink is strictly carnivorous. Because of its semiaquatic habits, it obtains about as much food on land as in water. Mink are opportunistic feeders with a diet that includes mice and rats, frogs, fish, rabbits, reptiles, crayfish, muskrats, squirrels, insects, birds, and eggs.