The Cricetidae family includes the voles, lemmings, hamsters and New World rats and mice that, collectively, incorporate nearly 700 species in 130 genera and are distributed on every continent. Voles are classified together with the lemmings and muskrats in the Arvicolinae subfamily and this group are the most populous group of rodents in the northern hemisphere. Europe is home to 18 vole species, while in Britain we have only three: the bank, field (Microtus arvalis) and water vole (Arvicola amphibius).
The nomenclature of the bank vole, indeed of all “red-backed” voles, has long been the subject of contention, with several genera appearing in the historical literature, including Hypudaeus, Evotomys, Clethrionomys and Myodes. For many years, the bank vole was classified as Clethrionomys glareolus, but in 2003 Michael Carlton and colleagues pointed out that the oldest formal association of Myodes with this group was made by Prussian zoologist and botanist Peter Pallas in 1811, predating German naturalist Wilhelm Tilesius von Tilenau’s Clethrionomys (meaning “chink” or “keyhole” mouse) by some 39 years and therefore taking priority. This was accepted by the ICZN in 2005 and since then the correct Latin/scientific name for the bank vole has been Myodes glareolus. The Greek myodes means “mouse-like” and the Latin glarea refers to “gravel” (presumably, bank) such that the Latin name translates roughly to “the gravel/bank-living mouse-like animal”.
That which follows is a summary of bank vole natural history. The detailed article for this species will follow in due course.
The Bank vole at a glance
Size: Head and body length 8-12cm (3-5 in.) with tail no longer than half that (up to 7cm / 2.7 in.). Wide range of adult weight according to habitat; 14-40g (0.5-1.4 oz.) although typically 18-20g (0.6-0.7 oz.). Island races tend to be larger than mainland animals.
Colour/Appearance: Reddish-chestnut brown fur, often greyer on flanks and silver-grey to whitish stomach; juveniles greyer cf. adults. Small black eyes and small but broad ears only just taller than surrounding fur. Short tail, blunt pale pink rounded nose surrounded by long whiskers. Some populations (e.g. in Hampshire) exhibit very dark, almost black, pelage.
Distribution: Found throughout Europe and central Asia, as far north as northern Finland, east into eastern Russia and south into the Mediterranean, although absent from Portugal and all but northern reaches of Spain. Present throughout England, Wales and Scotland, although distribution is patchy in far north and west. Found in Listowel, Co Kerry in Republic of Ireland in 1964, having apparently been deliberately introduced (poss. From Germany as early as 1920s) and now established in south-west.
Habitat: Inhabits wide range of habitats including woodland (deciduous, mature coniferous and, in Europe, taiga), mixed farmland, scrub and even fenland and bogs, although often seems to prefer drier areas. Also found in areas with high herb growth, banks and hedges such as railway embankments, road verges, riverbanks, parkland and sometimes gardens. Requirement for fairly dense ground cover makes them less common in city gardens vs. wood mice.
Longevity: Survival to second winter rare, oldest individuals probably 18-21 months. Animal of unknown sex kept at London zoo in early 1900s died just short of 5 yrs.
Sexing: Impossible to determine sex without handling and even anal-genital distance not necessarily accurate method; Mediterranean study mis-sexed 15-100% of males vs. molecular analysis.
Activity: Active day and night, although dawn and dusk peaks and more diurnal in winter. May exhibit 2-6h activity rhythm. During periods of heavy snow cover, voles remain active in subnivian zone, moving around in a series of tunnels and pockets under the snow. Does not hibernate. Quick darting run cf. wood mouse’s hop. Can climb well (esp. males) to reach fruit and seeds. May move comparatively large distances (several hundred metres); 930m (0.6 mi.) recorded for males during breeding season.
Territory/Home Range: Size varies widely according to habitat, age, sex and season, ranging from ~380-7,300 sq-m (0.09-1.8 acre); typically ~1,400 sq-m (0.35 acre) in deciduous woodland. Female ranges exclusive during breeding season but overlap thereafter; those of males larger and overlap with both sexes year-round. Females may allow daughters to live, but not breed, in home range. Defence of territory documented in lab, but rare in wild where mutual avoidance appears to prevail. Largely sedentary and highly faithful to site (esp. females) with strong homing ability up to ~700m (0.4 mi.) outside home range.
Creates shallow subterranean nest with radiating tunnel network leading to multiple entrances, often among tree roots or under logs. Ball-shaped nest composed of locally available materials (particularly grass, leaves and moss).
Diet and Feeding: Primarily herbivorous with 40-50% diet green leaf matter; smaller proportion of seed, fruit and animal matter. Dead leaves eaten during winter and fungi, roots, flowers, buds, grass, moss and invertebrates (esp. insects, earthworms and slugs) taken occasionally. Caches food under logs, in leaf litter or in tunnel walls in north of range. Seeds carried in “false cheek pouches”. Feeds where food found; on ground, in burrow system or in trees/bushes. Highly efficient digestion and gut anatomy changes to adapt to variations in diet.
Reproduction: Breeding season in most of UK March/April to September/October; shorter and more intense on islands. Bountiful food and mild temperatures protract season. Induced ovulators; highly fertile after first pregnancy. Breeding nests built in burrow system or sometimes tree holes. Litter of 3-5 (max. 8) pups (2g/0.07 oz.) born after 16-20 day gestation. Leave nest for short periods ~15 days. Lactation lasts 17-18 days, at which point pups weaned and weigh ~10g (0.35 oz.). Multiple paternity common (~25% litters in one Polish study). Parental care by female alone and pups sexually mature ~5 wks, although late born pups may not mature until following spring and most won’t breed until ~8 wks.
Behaviour and Sociality: Broadly gregarious with apparent dominance hierarchy that affects mating chances in males. Well developed use of scent; can distinguish individuals of own race/subspecies (e.g. mainland vs. Skomer) based on odour. Females recognise scent of mate and prefer it over that of stranger. High pitched vocalisations made during aggressive encounters and courtship; experienced males vocalise more then inexperienced ones. Responds to bird alarm calls.
Predators: Have wide range of predators, including cats, foxes, badgers, stoats, weasels, martens, adders, kestrels, buzzards, corvids and owls. Barn owl probably most significant owl predator.
Threats: Abundant and adaptable species not considered threatened or provided with any specific protection in Britain. Susceptible to lead poisoning (motorway verge populations) and to agricultural chemicals.
Collins Field Guide: Mammals of Britain and Europe - by David MacDonald and Priscilla Barrett
HarperCollins Publishers -- 1993 -- ISBN: 978-0002197793
Mammals of the British Isles: Handbook, 4th Edition - by Stephen Harris and Derek Yalden (eds)
The Mammal Society -- 2008 -- ISBN: 978-0906282656
The natural history "bible" covering all British mammals with detailed coverage of their biology, behaviour, ecology and taxonomy written by experts in the field and referenced to the primary literature.
The Encyclopaedia of Mammals - by David MacDonald (ed.)
Brown Reference Group -- 2006 -- ISBN: 978-0199206087
UK Mammals: Species Status & Population Trends - by The Tracking Mammals Partnership
JNCC/TMP -- 2005 -- ISBN: 978-1861075680
Urban Mammals: A Concise Guide - by David Wembridge
Whittet Books -- 2012 -- ISBN: 978-1873580851