The Bank Vole (Myodes glareolus)
FACTS AND FIGURES
Recognition: Reddish-brown fur above, creamy-grey fur below, rounded snout, less prominent eyes than mice and ears completely covered with fur; more sleek appearance than field vole, and rather longer, bicoloured (black above, white below) tail. Head/body length: 79-117mm; tail 33-48 mm, c. 50% of head and body. Weight: 20-35g Lifespan: The average life span of a bank vole is <1 year so population turnover is rapid. Diet: It feeds on a range of berries and seeds, leaves of herbs, shrubs and trees and some animal material (snails, insects). Soft fleshy fruits and leaves of shrubs are preferred.
Bank voles are found throughout mainland Britain, but on few of the islands. However, unlike field voles, they are now found in (southern) Ireland, as a result of an accidental introduction in the 1950s or earlier. Distinctive races (larger than on mainland Britain) occur on Skomer, Mull and Jersey.The bank vole occurs typically in deciduous woodland and hedgerows, preferring areas where there is some ground cover (brambles are good!). It needs much more water than the wood mice that share its woodland, so eats less of the dry seeds that wood mice prefer. Bank voles nest underground in burrows, but these are little studied. It is frequently disturbed in daytime at the entrance to its burrow, into which it disappears so fast that it is rarely seen – just the movement registers. Bank voles are more active in daylight than wood mice, and seem to be avoiding them. The breeding season begins in March/April and ends in September/ October in most years; an abundant seed crop can cause the breeding season to continue into winter. Four or five young are normally found in each litter and females will give birth to five or six litters each year. Early born young may mature and breed in their first year, later born young over winter to breed the next year. Voles do not hibernate but moult to cope with the inevitable change in temperature with the seasons. Moulting provides a dense layer of fur for winter and a "lighter" coat in spring. Like all small mammals, the bank vole is host to a number of parasites, carrying fleas, mites and worms. It is rarely taken by barn owls, but is an important prey for tawny owls, and for mammalian predators, especially fox, weasel, stoat and pine marten.
Bank voles are very widespread and are among the most common of British mammals; a recent population estimate put the number of bank voles in Britain at 23,000,000 and they occur at densities of 25/ha in spring. On Skomer, with no field voles around, densities can reach as high as 475/ha in autumn. Although the bank vole is numerous, it is an important part of the diet of tawny owls and small mustelids (weasel, stoat, pine marten), so it is still important to consider its conservation to maintain abundance. A varied woodland will encourage small mammals and ground cover such as groups of branches and bramble are very important for bank voles. They should be left when clearing patches of ground.
Gurnell, J & Flowerdew J.R. (2006) Live Trapping Small Mammals: A Practical Guide. (4th edn., revised). The Mammal Society, Southampton Harris, S. & Yalden, D.W. (2008) Mammals of the British Isles: Handbook, (4th edn.) The Mammal Society,