The Bank Vole Myodes glareolus is small (head and body 88 to 101 mm) with a tail up to half the length of the body. The ears are not as large as the mice but are larger than the Field Vole Microtus agrestis. It has a chestnut back which gives way to greyish on the sides and whitish underneath. Young animals are greyer and may be difficult to separate from the Field Vole but have a longer tail and slightly larger ears. There is little variation in colour.
They are found in a variety of habitats; it is essentially a woodland animal but is also found in hedgerows, field margins and gardens. The nest is normally in a burrow a few inches below ground level but can be in a tree trunk or other hollow. Around the nest it forms a system of burrows and tunnels in the field layer and so requires good cover and litter layer. It climbs freely and will use bird’s nests as feeding platforms.
Diet is mainly shoots, leaves, berries, nuts, seeds and fungi but can contain various insects and other invertebrates including snails. Burton (1968) says that up to a third of the diet can be invertebrates and even small birds and shrews can be eaten. When feeding on hazelnuts it leaves a distinctive hole in the shell with no teeth marks on the outer surface. This distinguishes it from Wood Mouse Apodemus sylvaticus which does leave teeth marks on the outer surface. Dormice Muscardinus avellanarius leave angled teeth marks on the cut surface of nuts, the other two leave vertical marks. Bank Voles do occasionally venture indoors and raid human larders.
Bank Voles start breeding in early spring and continue until the autumn. Up to five litters per year of three to six young can be born. Females born in the early part of the season can breed the same year. The breeding season can be lengthened by increased temperature and increased food supply but can be shortened in seasons of high population density. There is no indication of cyclical population changes like those of the Field Vole, but populations do vary, particularly in association with food availability. Good autumn seed crops can see larger numbers through the winter and affect the population until the following autumn.
Predation on voles is heavy, particularly by owls and Weasel Mustela nivalis, but other species are also important, for example Stoat Mustela erminea, Fox Vulpes vulpes, Domestic Cat Felis catus, Kestrel Falco tinnunculus, Carrion Crow Corvus corone, Rook Corvus frugilegus and Grey Heron Ardea cinerea. Bank Vole remains in owl pellets can be separated from Field Vole remains by the presence of an extra lobe on the upper second molar tooth in the latter, and the zigzags of the teeth are also more rounded than those of the Field Vole (Yalden, 1977). Wet weather is thought to have some advantage for Bank Voles, which makes them less likely to be heard and therefore less likely to be taken by owls (Flowerdew, 1993).
In the North East our map of records shows Bank Voles to be widely distributed across the region though most records are from the east of the area. This is believed, in the main, to be an effect of observer distribution, but in the extreme west, where they will avoid the uplands and open country, a thinner distribution is probable. More widespread live trapping or examination of owl pellets would probably show a better spread of records. They are perhaps the species that is most readily caught in Longworth traps and made up almost half of the 358 small mammals caught at various sites in the North East by Veronica Carnell (V. Carnell, pers. comm., 2012). They made up just over 6% of the total number of prey remains from 671 Long-eared Owl Asio otus pellets from Urlay Nook, the same proportion as Wood Mouse Apodemus sylvaticus, though the latter is a much more frequently recorded species, probably due to its closer association with human habitations. Outside the North East it is found generally throughout the country, but was missing from Ireland until it was accidentally introduced there probably in the 1920s from Germany (Shore and Hare in Harris and Yalden, 2008).
Written by Don Griss (last updated Nov 12)