Impact

Mink are generalist, opportunist predators, taking a wide variety of prey. The diets of the two sexes in one area can be very different with larger males preying on larger food items than females. Both Sexes tend to specialise on mammals and birds followed by fish, compared to otters, which are fish specialists. This section looks at their diet in general and the ecological and economic impact they may have.

Water Vole

The most ecologically significant impact of mink is almost certainly on water voles, which have undergone one of the most serious declines of any native British mammal over the last century. Mink predation has been shown to cause the local extinction of water voles from some catchments in Oxfordshire, Leicestershire and the North York Moors. They also determine the distribution of water voles in the Thames catchment. Overall, water voles have disappeared from 94% of the sites that they used to occupy and the impact on numbers is probably even greater as they are also now at a lower density where they do occur. Although habitat reduction and water quality are also issues in some areas, mink are the most serious threat to this native species.

Water voles have also vanished from whole catchments in north-east Scotland where another large scale mink control project is also under way. Details of this project can be found at www.rafts.org.uk/scottish-mink-initiative/

Click image to enlarge.

Other Mammals

They are an opportunistic predator and, in addition to water voles, mink take a variety of other mammals. Where they are abundant, rabbits are often the most heavily predated species and are often the most abundant food. Small terrestrial mammals are also taken along with occasional brown hares but there is no evidence of an impact on the populations of these other species.

One of the most interesting interactions may be with otters. There is evidence (Oikos, 106, 9-18) that where areas are recolonised by otters, evidence of mink declines. This indicates that mink are either feeding further from water courses or populations have declined. The interaction between the species is very unlikely to lead to the elimination of mink as they can more easily exploit terrestrial foods so the species are likely to co-exist.

Birds

The main impact on birds has been on coastal seabird breeding colonies. In western Scotland mink caused widespread whole-colony breeding failures of Black-headed Gulls, Common Gulls and Common Terns at colonies on small islands along 1000 km of mainland coast. After one or more years of such failure, most of the affected breeding sites held no birds or greatly reduced numbers. On inland waterways, ducks, moorhens and coot are the most commonly predated species. Although not a major proportion of their diet, they will take eggs or young chicks when available, which can have a significant impact on rare or locally scarce species. Kingfishers are one example and often very vulnerable because they usually nest in tunnels they make in earth banks on the sides of rivers, lakes or man-made ditches. Mink are often able to claw up the bank and get into the kingfisher nest and clean it out, this was seen on an episode of BBC’s Springwatch in June 2012.

Gamebirds and poultry are also taken, where this does occur, the impact on individual rearing pens or poultry flocks can be very significant.

Mallard

Moorhen
© T.A.Taberham
Water Rail
© T.A.Taberham

Oystercatcher

Lapwing

Swan with cygnets

Kingfisher

Click image to enlarge.

Fish

Species that are taken tends to relate to availability; in rivers with game fish 34% of their diet can be salmonids, whereas on other rivers eels are frequently taken as they are relatively easily predated. Mink can be a particular problem both with small collections of fish and at commercial fisheries. In a recent survey of commercial fisheries in Wales, for example, 30% reported that mink were a problem, despite only 50% having mink in their area. Although mink prefer smaller fish they do take larger fish and predation on individual high value fish can lead to a significant cost for fisheries and individuals.

Other Species

A range of other foods are taken infrequently; these include frogs, snakes, beetles, earthworms and molluscs. Crayfish seem to be a favoured food and may be heavily predated where they are found, which may be an additional threat to the threatened native white-clawed crayfish.