Stopping the Water Vole Killer

I have often referred on this blog to the number of mammal species that are currently faced with extinction, of being wiped totally from the face of the Earth. Depending on how strictly you want to define the threat, this could be anything up to 25% of the total known species, although it's worth noting that a great many other species have declining populations, if not ones that are likely to vanish altogether any time soon.

For many species, even if extinction is not a threat, extirpation can be. This is, essentially, a local extinction, where the species dies off entirely in some particular area, but still survives somewhere else. While it can be any area you like, in conservation terms, we tend to be talking about either countries or reasonably sized islands. Or, as is the case in Britain, both.

Many species of mammal have been extirpated from the British Isles over the course of our history. Wolves are one of the more famous examples here, with the last official record of a dead wolf dating from 1680 in Scotland (it's unlikely to have literally been the last, and rumours continued for another hundred years or so, although it's hard to know how many of them were accurate). In a number of other cases, such as the hazel dormouse, local populations today very much seem to be in decline.

Weasels on the Riverbank: Mink

European mink

While most are still terrestrial, the long sinuous bodies of weasels are easily adapted to an aquatic lifestyle. Within the lineage that led to the modern weasels and their relatives, semi-aquatic habits have evolved at least three times. The first of those lines led to the otters, but the most recent led instead to the European mink (Mustela lutreola), a much smaller animal that is clearly not an otter, and is, in fact, most closely related to the ferrets and polecats.

The European mink was once found throughout central and eastern Europe, from Germany in the west to European Russia in the east. It is almost as aquatic as an otter, and is never found far from fresh water, preferring dense vegetation along the banks of fast-flowing streams and small rivers. Its feet are partially webbed, and it is a good swimmer in comparison to most other members of its family, although not as skilful as the otters. Mink den in natural hollows, such as those beneath tree roots, and will also take over the burrows of their favourite food, water voles.

Even so, while they are undeniably well adapted to a semi-aquatic lifestyle, they are no match for otters. For example, mink do not see well underwater, and only dive after fish, crayfish, and so on, after they have spotted them from above the surface. Given that otters and mink both inhabit the same parts of Europe, why aren't the latter simply out-competed? It turns out that it's their very lack of adaptation that helps them survive.