Social and territorial behaviours in
Portland, Maine. American mink territories are held by individual animals with minimal intrasex overlap, but with extensive overlap between animals of the opposite sex. Most territories are in undisturbed, rocky coastal habitats with broad
littoral zones and dense cover. Some are on estuaries, rivers and canals near urban areas. Home ranges are typically long, with male territories larger than females'. The American mink's dens are characterized by a large number of entrances and twisting passages. The number of exits varies from one to eight. During aggressive interactions, mink assert their dominance by arching their backs, puffing up, lashing out their tails, and stomping and scraping the ground with their feet, while also opening their mouth in a threat-gape. Should this be unsuccessful, fights may result, with injuries to the head and neck. The start of
mating season ranges from February in its southern range to April in the north. Males commonly fight during the mating season, which may result in the formation of loose, temporary dominance hierarchies governing access to receptive females. Exceptionally large litters of 11 kits have been recorded in Tartaria and 16 in the United States. The American mink often kills birds, including larger species like
seagulls and
cormorants, by drowning. In its natural range, fish are its primary prey. Although inferior to the
North American river otter in hunting fish,
Audubon and
Bachman once reported seeing a mink carrying a foot-long
trout. Mink inhabiting the
prairie sloughs primarily target frogs,
tadpoles, and mice. It is a formidable predator of
muskrats, which are chased underwater and killed in their own burrows. Among the rodents killed by the American mink in its native range are rats and mice of the
genera Hesperomys,
Microtus,
Sigmodon, and
Neotoma.
Marsh rabbits are frequently taken in marshy or swampy tracts. In
Tartaria, the American mink's most important food items are
voles, fish, crustaceans, frogs, and aquatic insects. In winter, aquatic foods predominate, while land-based prey increases in importance during the spring. Within the
Altai Mountains, the American mink feeds predominantly on mammals such as rodents, shrews, and moles, as well as birds, reptiles, amphibians, and fish. Among the 11 different bird species preyed upon by minks in Altai are
dippers and
pine grosbeaks. Among fish, small species predominate in the diet of minks in Altai, and include
minnows,
gudgeons, and wide-headed
sculpins. In the
Sverdlovsk and
Irkutsk Oblasts, mouse-like rodents are their most important foods, followed by birds, fish and insects. In the
Russian Far East, where crustaceans are scarce, the American mink feeds extensively on
amphipods. In the
British Isles, dietary composition varies seasonally and regionally.
European rabbits are the most commonly taken prey in areas where they are common, especially in summer. A range of small rodents and insectivores are preyed upon, but to a lesser degree.
European hares are occasionally attacked. Minks in Britain prey on several bird species, with ducks,
moorhens, and
coots being most frequently targeted on lakes and rivers, while
gulls are taken in coastal habitats. Marine species preyed upon in Britain include
European eels, rock-pool fish such as
blenny,
shore crabs and
crayfish. American minks have been implicated in the decline of the
water vole in the United Kingdom and linked to the decline of waterfowl across their range in Europe. They are now considered vermin in much of Europe and are hunted for the purpose of
wildlife management. In South America's
Cape Horn Biosphere Reserve, mammals, including both native and exotic rodents, are the American mink's main prey throughout the year, though birds are of equal importance during their summer nesting periods. The American mink may pose a threat to poultry. According to
Clinton Hart Merriam and
Ernest Thompson Seton, although the American mink is a potential poultry thief, it is overall less damaging than the
stoat. Unlike the stoat, which often engages in
surplus killing, the mink usually limits itself to killing and eating one fowl during each attack. Studies in Britain indicate poultry and game birds only constitute 1% of the animals' overall diets;
Relationships with other predators The American mink replaces and sometimes kills the European mink wherever their ranges overlap. The decline of European mink populations seems to coincide with the spread of the American mink, but "The early declines in Central Europe and later in Finland took place before the spread of the American mink." The diets of the American mink and
European otter overlap to a great extent. In areas where these two species are sympatric, competition with the otter for fish causes the American mink to hunt land-based prey more frequently. Large
birds of prey, such as
bald eagles (
Haliaeetus leucocephalus) and
great horned owls (
Bubo virginianus) occasionally hunt American mink. In
Finland,
white-tailed eagles (
Haliaeetus albicilla) have become the main natural control and may inhibit the mink from breeding via heavy predation.
Eurasian eagle-owls (
Bubo bubo) also can be predators of mink in the introduced regions. In Florida (specifically southern Florida), American minks may be eaten by some growth stage of invasive snakes such as
Burmese pythons,
reticulated pythons,
Southern African rock pythons,
Central African rock pythons,
boa constrictors,
yellow anacondas,
Bolivian anacondas,
dark-spotted anacondas, and
green anacondas. ==Intelligence==