American Mink are primarily nocturnal and crepuscular but also may be active during the day. The species is semi-aquatic, and it spends much of its time foraging in water. It hunts along the water's edge when food is abundant, but it will seek food in nearby terrestrial habitats when necessary. Their most common den sites are hollow logs or muskrat lodges. Notwithstanding their semi-aquatic habits, mink are not as highly adapted for an aquatic existence as the North American River Otter and certain other species.
Mink generally live no longer than 3 years in the wild, but some live 8 years or more in captivity.
The mink's diet is subject to seasonal and local variation. However, they are highly carnivorous, rarely eating any vegetable material. Prey species include frogs, snakes, crayfish, other invertebrates, fish, muskrats, and aquatic birds. Crayfish or muskrats often make up more than half of the diet. In some circumstances, waterfowl, including grebes, coots, and ducks are eaten in abundance. Winter foods reflect less dependence on crayfish and muskrats and more time spent foraging away from water. Animals eaten during winter include mice, rabbits, and squirrels. Mink often kill many more animals than they can eat, and they cache the remainder for later use. One food cache found in Illinois in January contained 13 freshly killed muskrats, 2 mallards, and a coot.
Animals that prey on mink include Coyotes, foxes, Bobcats, and Great Horned Owls. However, probably as many mink are killed by other mink as by all other natural predators combined. Other sources of mortality include starvation and diseases such as tularemia and rabies. Finally, mink are favored by fur trappers, and trapping thus is the most important cause of mortality.
Breeding occurs throughout the year but is concentrated in spring and late summer. Courtship is initiated when an estrous female allows a male to approach. After vigorous struggling and fighting, the male grabs the female by the scruff of the neck and holds her down. Copulation is repeated over several days. Ovulation is induced by repeated copulation. Gestation lasts 34 to 37 days, and the number of young per litter typically is 4 or 5. Females usually produce 2 or 3 litters per year. Newborn are blind and naked but are covered with a fine, white coat of fur by about 4 days of age. Their adult fur develops between 2 and 3 weeks after birth. Their teeth erupt at 2 weeks, and their permanent dentition develops between 30 and 49 days. The young begin to eat solid food at about 3 weeks. Their eyes open between 26 to 32 days. Shortly after their eyes open, they begin to leave the den. At this time the female teaches the young to kill prey, and by 6 or 7 weeks after birth they are proficient hunters. At 8 weeks of age, the young males are larger than the females. The young reach adult size between 12 to 14 weeks and probably disperse at about that time. American Mink become sexually mature at approximately 4 months of age. The male plays no role in caring for the young.