American mink (Neovison vison)

Naming▲ Back to top

*Cree: ''Sang-gwiss'', ''Shakzuashew'' or ''Atjackasheiv''
⤷ Ojibwe: ''Shang-gwes'-se''
⤷ Chipewyan: ''Tel-chu'-say''
⤷ Ogallala Sioux: ''Lo-chin'-cha''
⤷ Yankton Sioux: ''Doke-sesch''As of 2005, 15 subspecies are recognised.

Behavior▲ Back to top

American mink territories are held by individual animals with minimal intrasexual overlap, but with extensive overlap between animals of the opposite sex. Most territories are located in undisturbed rocky coastal habitats with broad littoral zones and dense cover. They may also occur on estuaries, rivers and canals near urban areas. Home ranges are typically 1–6 kilometres long, with male territories being larger than those of females. As long as it is close to water, the American mink is not fussy over its choice of den. Mink dens typically consist of long burrows in river banks, holes under logs, tree stumps or roots and hollow trees, though dens located in rock crevices, drains and nooks under stone piles and bridges are occasionally selected. Burrows dug by American minks themselves are typically about four inches in diameter and may continue along for 10–12 feet at a depth of 2–3 feet . The American mink may nest in burrows dug previously by muskrats, badgers and skunks, and may also dig dens in old ant hills. The nesting chamber is located at the end of a four-inch tunnel, and is about a foot in diameter. It is warm, dry and lined with straw and feathers. The American mink's dens are characterized by a large number of entrances and twisting passages. The number of exits vary from 1-8.

The American mink normally only vocalises during close encounters with other minks or predators. Sounds emitted by the American mink include piercing shrieks and hisses when threatened and muffled chuckling sounds when mating. Kits squeak repeatedly when separated from their mothers. Ernest Thompson Seton reported hearing minks growl and snarl when confronting a threat. During aggressive interactions, the American mink asserts its dominance by arching its back, puffing up and lashing its tail, stamps and scrapes the ground with its feet and opens its mouth in a threat-gape. Should this be unsuccessful, fights may result, with injuries to the head and neck.

Reproduction▲ Back to top

The American mink is a promiscuous animal, which does not form pair-bonds. The mating season for American minks begins from February in its southern range to April in the north. In its introduced range, the American mink breeds one month earlier than the European mink. Males commonly fight during the mating season, which may result in the formation of loose, temporary dominance hierarchies governing access to receptive females. The mating season lasts for three weeks, with ovulation being induced by the presence of males. The mating process in the American mink is violent, with the male typically biting the female on the nape of the neck and pinning her with his forefeet. Mating lasts from 10 minutes to four hours. Females are receptive for 7-10 day intervals during the three week breeding season, and can mate with multiple males. Along with the striped skunk, the American mink is among the only mammals to mate in spring whilst possessing a short delay before the occurrence of implantation. This delayed implantation allows pregnant minks to keep track of environmental conditions and select an ideal time and place for parturition.

The gestation period lasts from 40–75 days, with actual embryonic development taking place after 30–32 days, thus indicating that delayed implantation can last from 8–45 days. The young are born either in April or June, with litters consisting of four kits on average. Exceptionally large litters of 11 kits have been recorded in Tartaria and 16 in the United States. The kits are blind at birth, weighing six grams and possessing a short coat of fine, silver-white hairs. The kits are dependent on their mother's milk, which contains 3.8% lipids, 6.2% protein, 4.6% sugar and 10.66% mineral salts. Their eyes open after 25 days, with weaning occurring after five weeks. The kits begin hunting after eight weeks of age, but stay close to their mother until autumn, when they become independent. Sexual maturity is attained during the kit's first spring, when they are about 10 months old.

Food▲ Back to top

The American mink is a carnivorous animal, which feeds on rodents, fish, crustaceans, amphibians and birds. It kills vertebrate prey by biting the back of the head or neck, leaving canine puncture marks 9–11 mm apart. In its natural range, fish are the American mink's 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, 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 genus ''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 the American mink's 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. Aquatic species preyed upon in Britain include European eels, rock-pool fish such as blenny, shore crabs and crayfish. American Mink have been implicated in the decline of the water vole in the United Kingdom and linked to the decline of water fowl across their range in Europe. They are now considered vermin in much of Europe and are hunted for the purpose of wildlife management. In the 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 period.

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 that poultry and game birds only constitute 1% of the animal's overall diet.

Predators▲ Back to top

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. The diets of the American mink and European otter overlap to a great extent. In areas where the two species are sympatric, competition with the otter for fish causes the American mink to hunt land-based prey more frequently.

Evolution▲ Back to top

As a species, the American mink represents a more specialised form than the European mink in the direction of carnivory, as indicated by the more developed structure of the skull. Fossil records of the American mink go back as far as the Irvingtonian, though the species is uncommon among Pleistocene animals. The fossil range of the American mink corresponds with the species' current natural range. The American minks of the Pleistocene did not differ much in size or morphology from modern populations, though a slight trend toward increased size is apparent from the Irvingtonian through to the Illinoian and Wisconsinan periods.

Although superficially similar to the European mink, studies indicate that the American mink's closest relative is the kolonok of Asia. The American mink has been recorded to hybridize with European minks and polecats in captivity, though the hybrid embryos of the American and European minks are usually reabsorbed.

Uses▲ Back to top

Wild mink can be tamed if caught young, but can be treacherous, and are usually not handled bare-handed. In the late 19th century, tame American minks were often reared for ratting, much as ferrets were used in Europe. They are more effective ratters than terriers, as they can enter rat-holes and drive rats from their hiding places. Because of their fondness for bathing, captive American minks may enter kettles or other open water-containing vessels. When minks of wild stock are confined with tame ones, the latter invariably dominate the former. They have also been known to dominate cats in confrontations. Though intelligent, mink are not quick to learn tricks taught to them by their owners. Even though domestic mink have been bred in captivity for almost a century, they have not been bred to be tame. Domestic mink have been bred for size, fur quality, and color. However, the US Fur Commission claims that "mink are truly domesticated animals" based on the number of years they have been kept on fur farms.