The American Mink (Neovison vison) (previously Mustela vison)
FACTS AND FIGURES
Recognition: Usually dark brown fur, looking black when wet. Because of captive breeding for fur, mink can be almost any colour from white through marbled grey to chocolate brown/black. Small, variable white patches on chin, throat, chest and groin, though not always visible on the live animal, more evident on a carcass. Shortish fluffy tail; the size of a ferret or polecat, but generally much darker overall. Head/body length: males 33-45cm, females 32-37cm. Tail length: males 15-22cm, females 13-19cm. Weight: males: 0.8-1.5kg, females: 0.4-0.8kg. Lifespan: Mink have lived up to 6 years in the wild. Diet: Mink eat a wide range of mammals, birds and fish, typically about a third of the diet coming from each; in some areas they also eat invertebrates, such as crabs and crayfish. Among mammals, rabbits are an important food; aquatic birds, especially coots and moorhens, are favoured; and among fish, eels are especially vulnerable.
Mink are found in throughout Great Britain and Ireland, and on some off-shore islands. They are an invasive non-native species, originally brought to fur farms from their native North America and subsequently escaping or being misguidedly released. It is now illegal to keep them without a licence; the last fur farms were closed in 2003 (Scotland) or 2004 (England and Wales). Mink are essentially amphibious, and are typically found along rivers and coastal areas. Though less aquatic than the much larger otter, they can swim strongly, and, exceptionally, can dive for up to a minute to depths of 3m. They are certainly capable of swimming to islands within 1 km of the mainland, but were separately introduced to Harris and Lewis, whence they spread to North Uist. The mink’s success is in part a result of its ability to exploit a very wide range of prey, and especially to take advantage of any species that is locally or seasonally abundant. Thus a nesting seabird colony is very vulnerable for the limited period of its breeding season, a good water vole colony provides easy meals, and a captive flock is especially vulnerable. Mink climb well, as well as swimming easily, so fences have to be good to exclude them. Mink are strictly territorial, males occupying exclusive ranges of 1-6 km in length. Females have smaller territories within or overlapped by those of males. They use their evil-smelling scats to mark the boundaries of their territory, and the neighbourhood of their den, which is usually within 10 m of the water. The female has just one litter a year, and young mink are born blind and hairless, in litters of 4-6, in May. They begin to take meat from 5-6 weeks, and reach adult size by the autumn. They can breed at one year old. Mating is rough, with the bigger male grasping the female’s nape. Pregnancy includes a variable (11-48 day) delay in implantation, and an active pregnancy of around 28 days. Male mink play no direct part in rearing the young.
In the early years of its establishment in Britain and Ireland, mink appeared to do little serious damage, despite much concern about their potential impact. However, at least two serious impacts have been recorded. Some seabird colonies on offshore islands within the swimming range of mink have suffered severe losses of both adult and young birds. In some cases, birds have moved to other, more remote, islands, but, for instance, black guillemots, which nest sparsely in scree slopes, seem to be very vulnerable. Water voles, confined to a strip of riverside habitat, have proved to be very vulnerable, and their population plummeted in the 1990s. As a consequence, serious attempts have been made to remove mink from river systems where water voles might be favoured, and from offshore islands, especially the Outer Hebrides, where ground-nesting birds should be abundant (in the absence of all the usual terrestrial predators). Effective control is based on the use of mink rafts; these have clay floors, enclosed in a tunnel, which reveal when mink are present; the clay tray can then be supplemented by a trap, and any mink caught can be shot. In the Outer Hebrides, a cage-trapping campaign has already eliminated them from North Uist.
Dunstone, N. (1993). The Mink. T. & A.D. Poyser, London.
Harris, S. & Yalden, D.W. (2008) Mammals of the British Isles: Handbook, 4th edn. The Mammal Society,