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American mink (Neovison vison) are a member of the Mustelid family whose other members include weasels, otters and badgers. They all have a musk gland which excretes pungent smelling oil which they use to mark their territories.
There are two species of mink: the European mink (Mustela lutreola) and the American mink. The European mink is native to continental Europe and is thought to have occurred in the UK about 400,000 years ago. American mink is native to North America but is now found across much of the world due to human intervention.
- How American Mink Arrived in the UK
In many parts of the world American mink are bred in farms for their thick glossy fur. The first mink farm opened in England in 1929. The first farm opened in Scotland in 1938, where they were recorded in the wild the same year.
The first records of breeding in the wild were in 1962 from the river Ugie in N.E. Aberdeenshire where it was reported that mink had probably been breeding 'for some time', and from the river Deveron, Moray.
The population we have today are the descendants of mink who either escaped from the farms or were deliberately set free by animal rights activists.
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Like weasels (Mustela nivalis), mink have short legs, a long thick neck and a broad head with short rounded ears. Males are larger than females measuring 34 – 54 cm and weighing 1 – 1.6 kg. Females measure 30 – 45 cm and weigh 0.5 – 1 kg. For both sexes, the tails makes up about a third of total body length.
Their coat is most often a deep, rich brown and they sometimes have white markings on their throat. As unusual fur colours fetch higher prices at auction, the fur colour of mink in the UK varies from a very light silvery colour, to the natural dark brown, however unusual colourings such as purple-grey and albino (white) have also been recorded |
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American mink are semi-aquatic which means that they spend a lot of time in and around water. They are good, strong swimmers and have slight webbing between their toes which helps them swim quickly in the water. Although they will usually avoid swimming in strong currents, they have been found to swim across the sea to reach islands, sometimes up to 5km off shore.
In America, mink are usually found near water in areas with lots of tree cover as this provides cover from predators. In the UK, they are found in almost all aquatic habitats, but favour slower flowing rivers, burns and lochs where there is a plentiful supply of food. Research carried out by Aberdeen University suggests that in Scotland, American mink numbers are highest in coastal areas as these areas provide the most food.
Mink are carnivores and a generalist predator which means they do not have a specific diet and will eat whatever they catch. Their varied diet includes rabbits (Oryctolagus cuniculus), water voles (Arvicola terrestris), eggs, fish, ground nesting birds and even chickens. A result of their varied diet is that they can survive in many different habitats.
Another reason for their big impact on native species is their high metabolic rate which means they eat approximately one third of their body weight every day and that’s a lot of food.
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American mink are active 24 hours a day but are most active at dusk and dawn. Females are very territorial, defending their territories against other females and a male territory will include that of several females. They do not hibernate and so are active year round.
During spring (February to April) male American mink move vast distances across the country, up to 20km a day, in search of a mate. They will try to mate with any female they find and afterwards go in search of another. Females will also mate with multiple males to ensure they are pregnant.
Once the females have mated they will make a den sometimes in an old rabbit warren or water vole burrow. Gestation is around 39 days but embryo growth can be paused if they are at different stages of development which can happen when there are multiple fathers.
Up to 10 kits are born and they are weaned at about 6 weeks. In the summer months the kits leave the den and from around August, they disperse to find their own territories. Research carried out by the University of Aberdeen has shown that juveniles can travel over 100 km from their place of birth within a year so they can be quick to colonise new areas. |
American mink are native to North America and can be found in most of the United States and Canada with the exception of Hawaii, Arizona, southern California, southern and central Utah, southern New Mexico and western Texas. Due to their use in fur farms and a mink’s ability to ‘escape’, they are now found across large parts of Europe, Japan and South America.
The reason American mink have such a big impact on our native wildlife is because our wildlife has only had 50 years to adapt to American mink being here, whereas they have been in America for hundreds of thousands of years. In America, American mink have predators including the Coyote (Canis latrans), Wolf (Canis lupus), Brown bear (Ursus arctos), Bobcats (Lynx rufus) and the North American river otter (Lutra canadensis) whereas in the UK, they do not have any predators. To find out about the impact they have on our wildlife, please visit the Impacts page.
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- American Mink and European Otters in the UK
The American mink originally colonised the UK at a time when both otters and polecats were largely absent due to pesticide poisoning, overhunting and persecution, respectively. Both native species are now recovering nationally. The otter is approximately seven times larger than the mink, the polecat is very similar in size, and all three species consume potentially overlapping diets, occupy similar habitats, and are generally nocturnal. Studies by the Wildlife Conservation Research Unit (WildCru) at Oxford University of mink and otter diet in the Outer Hebridean islands, and in southern England, show that in the presence of otters, mink diet becomes more terrestrial yet the diet of otters changes relatively little. This suggests that, as expected from their relative sizes, otters are the dominant competitor and that where both species are found; mink are forced to undergo a dietary shift.
However, WildCru’s more recent comparative study, comparing mink abundance and behaviour before and after the re-arrival of otters and polecats on the River Thames suggested that mink were still abundant in the presence of these native competitors, but that they had changed their activity patterns. Whereas mink in the 1990s (in the absence of otters and polecats) were generally nocturnal, mink in the 2000s (in the presence of otters and polecats) were predominantly active during the day. It is thought that this temporal shift may be an avoidance mechanism allowing the coexistence of mink with native, nocturnal competitors.
In Scotland American mink are continuing to spread their range into areas already occupied by healty otter populations. Moreover, while the otter population in England was declining during the WildCRU study, the same cannot be said for the Scottish otter populations. |
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