Islands have a habit of coming up with distinctive species due to their isolation from mainland creatures of the same kind.
The St Kilda Wren is typical of this phenomenon of natural selection as are the unique birds and animals found on the Galapagos, Madagascar and other islands all over the world.
The Skomer Vole is another example, first identified as different by the Cardiff naturalist Robert Drane F.L.S. during a visit to the island in 1897 by the Cardiff Naturalists’ Society.
An acute observer, he first drew attention to the unusual size of the Skomer vole, reporting that, having meticulously measured the little rodent, he could not make its teeth agree with those of the English bank vole measured by the naturalist Lydekker two years earlier. Even the smallest Skomer vole’s teeth were larger than those of the bank vole, he discovered, and also commented on its difference from the mainland common field-vole. Sometimes referred to as the red-backed mouse, the Skomer Vole was the object of considerable scientific interest after Drane’s observations, and another naturalist named Barrett-Hamilton accorded it specific rank in 1903 after studying specimens caught by Dr Y. H. Mills of Haverfordwest. Barrett-Hamilton stated in 1914: “It is clear that to Drane belongs the honour of discovering this species,” but it was not until later that it was classified as a hitherto undescribed vole. It is an interesting fact that the vole is peculiar to Skomer while Skokholm, only a short distance away, has only the man-introduced house mouse and Ramsey, on the other side of St Brides Bay, has shrews and typical common bank-voles. A typical bank vole in appearance, but much larger, the Skomer Vole has a short, blunt head, small ears and eyes, a tail about half the length of its head and body, and a charactertistically reddish tinge to the rich fur along its back. Its large skull has certain structural peculiarities not present in its common mainland cousin. Organised parties visiting Skomer are fortunate enough to be able to see and sometimes handle the unique vole, as the island wardens know exactly where they can be found. A striking characteristic is their tameness and lack of aggression when caught, a gentle nature they do not always show to their fellows. The wardens on Skomer carefully monitor the voles, for they are vulnerable to predators, although there are no ground predators like rats or foxes, stoats, weasels or mink. The short-eared owls are very partial to voles, in fact they are their staple diet and their raison d’etre on the island, but buzzards also eat them and the peregrine falcon will occasionally take one if it presents itself, although they prefer larger avian prey. Trapping exercises over the years have indicated the population of voles on Skomer at between 17,000 and 27,000, with around 140 per acre in the more densely populated areas, so the Skomer Vole seems to be thriving.