Bank vole

Latin name

Myodes glareolus

Class

Mammals

Group

Mice & Voles

This species has experienced a tumultuous taxonomic history. Originally classified as a mouse (Mus glareolus) by German naturalist Johann von Schreber in 1780 based on a specimen from Denmark, it was subsequently moved into the Myodes ('mouse-like') genus in 1811 by Prussian zoologist Peter Simon Pallas. In 1850, Wilhelm Gottlieb Tilesius von Tilenau argued that it should be grouped with the other red-backed voles and moved it into Clethrionomys (from the Greek klethrion meaning 'alder grove' and mus for 'mouse'), and much of the literature refers to the species as Clethrionomys glareolus. Currently, Myodes glareolus has taxonomic precedent (i.e., is considered correct by the ICZN), based on the analysis of Michael Carleton and colleagues published in the Journal of Mammalogy during 2014, but it remains controversial with several authors having recently argued for this species to be formally recognised as Clethrionomys glareolus. (It should perhaps also be mentioned that several older texts refer to the species as being in the Evotomys ('true-eared mouse') genus, as this association persisted quite widely even until the 1930s.)

The specific name glareolus is derived from the Latin glarea for 'gravel', presumably implying bank.

The Bank vole at a glance

Size: Head and body length between 8-12 cm (3-5 in.) with tail no longer than half that (up to 7 cm / 2.7 in.). Wide range of adult weight according to habitat such that adults can weigh 14-40 grams (0.5-1.4 oz.), although typically 18-20 g (0.6-0.7 oz.). Island races tend to be larger than mainland animals.

Colour/Appearance: In common with all red-backed voles, the bank vole has short, thick, chestnut-brown fur along the head and upper section of the back, often paling to grey on the lower flanks and with an off-white, sometimes silvery-grey, underside -- juveniles tend to be greyer than adults. Some populations (e.g., in Hampshire) exhibit very dark, almost black, fur. The eyes are small, round, and shiny black with no discernible pupil even at quite close range. The ears are comparatively large and rounded but set low in the fur such that they barely alter the profile of the head, while the blunt nose is surrounded by long whiskers and pinkish in colour, as are the paws. The short-furred tail is darker on the dorsal surface and paler underneath.

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 the far north and west. Found in Listowel, County Kerry in the Republic of Ireland during 1964, having apparently been deliberately introduced (possibly from Germany as early as 1920s) and now established in south-west of the country.

Habitat: Inhabits wide range of habitats including woodland (deciduous, mature coniferous and, in Europe, taiga), mixed farmland, and scrub. Sometimes found in fenland and bogs, although generally 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 rural gardens. The Mammal Society, in their 2018 review, estimated the the preferred habitats being broadleaf woodland (accounting for 39% of records) and urban parks and gardens (22%), with dwarf shrub heath such as heather moorland being least favourable (4%). Their requirement for fairly dense ground cover makes them less common in city gardens than wood mice.

Longevity: Survival to their second winter is rare, with the oldest individuals probably reaching only 18-21 months. One animal of unknown sex kept in captivity at London zoo in the early 1900s died just short of 5 years.

Sexing: Impossible to determine sex without handling and, even then, the anal-genital distance not necessarily accurate method. One study of Mediterranean voles found anywhere from 15-100% of males were mis-sexed based on external anatomy vs. molecular analysis.

Activity: More likely to be seen during the day than wood mice, bank voles are active by day and night. Voles often seem to exhibit a 2-6 hour activity rhythm, with dawn and dusk peaks frequently reported - an increase in diurnal activity is recorded during winter, particularly during heavy ground frosts. Bank voles do not hibernate, and during periods of heavy snow cover they remain active in subnivean zone, moving around in a series of tunnels and pockets under the snow. Voles move with a quick "darting" run, readily distinguishable from the hop of the wood mouse, and can climb very well (males particularly) to reach fruit and seeds. Bank voles may move comparatively large distances, covering several hundred metres; one males was recorded travelling 930 m (0.6 mi.) during breeding season.

Territory/Home Range: Size varies widely according to habitat, age, sex, and season, ranging from ca. 380 to 7,300 sq-m (0.09-1.8 acre); ca. 1,400 sq-m (0.35 acre) seems typical in deciduous woodland. Female ranges are exclusive during breeding season but overlap outside of this, while those of males are larger and overlap with both sexes year-round. Females may allow daughters to live, but not breed, in their home range. Defence of territory has been documented in captivity, but seems rare in the wild where mutual avoidance appears to prevail. A largely sedentary species that's highly faithful to a given site (especially females), probably staying within ~50 m (164 ft.) of the nest, and with a strong homing ability up to about 700 m (0.4 mi.) outside their home range. Creates a shallow subterranean nest with a radiating tunnel network leading to multiple entrances, often among tree roots or under logs. The nest is ball-shaped and composed of locally available materials, particularly grass, leaves, and moss.

Diet and Feeding: Primarily herbivorous with 40-50% of the diet being green leaf matter; a smaller proportion of seeds, fruit, and animal matter. Dead leaves are eaten, usually during winter, while fungi, roots, flowers, buds, grass, moss, and invertebrates (especially insects, earthworms, and slugs) are taken occasionally. Food may be cached (stored) under logs, in leaf litter, and/or in tunnel walls. Seeds are sometimes carried away in "false cheek pouches", although voles generally feed where the food is found; on the ground, in their burrow system, or in trees/bushes. Digestion is highly efficient and their gut anatomy changes to adapt to seasonal variations in their diet.

Reproduction: Breeding season in most of UK runs from March/April to September/October, being shorter and more intense on some northern islands, but this can be protracted by bountiful food and mild temperatures. Bank voles are induced ovulators, meaning there is no regular oestrous cycle because the act of mating triggers ovulation rather than the light-dark ratio, and females are highly fertile after the first pregnancy. Breeding nests are built either in their existing burrow system or sometimes tree holes. Litters typically consist of 3-5 pups, occasionally up to 8, each weighing about 2 g (0.07 oz.), born after a 16-20 day gestation. Young will leave the nest for short periods/excursions from around 15 days old. Lactation lasts 17-18 days, at which point the pups weaned and weigh about 10g (0.35 oz.). Multiple paternity is common, with one Polish study finding around 25% litters had two or more fathers. Parental care is provided by the female alone and are pups sexually mature at around 5 weeks, although late born pups may not mature until the following spring. Most voles won't breed until they're at least 8 weeks old.

Behaviour and Sociality: A broadly gregarious with apparent dominance hierarchy that affects mating chances in males. Scent is pivotal in vole society and voles appear able to distinguish individuals of their own race/subspecies (e.g., mainland vs. Skomer) based on odour alone. Females recognise the scent of their mate and prefer it over that of unfamiliar individuals. High pitched vocalisations made during aggressive encounters and courtship, with experienced males apparently vocalising more then inexperienced ones. There are some observations that the species responds to bird alarm calls by increasing vigilance. Intriguingly, Stefan Buczacki mentions that they are commonly troublesome in gardens, being less timid than field voles, and commenting on how it's "the only vole bold enough to come into my house, despite the presence of a cat". I know of no known impacts of this species in gardens.

Predators: Have wide range of predators including cats, foxes, badgers, stoats, weasels, martens, adders, kestrels, buzzards, corvids, and owls. Barn and tawny owls are probably their most significant avian predators in Britain.

Threats: An abundant and adaptable species with a stable population that is not considered threatened and, as such, granted no specific protection in Britain. Data from motorway verge populations suggest the species is susceptible to lead poisoning and agricultural chemicals, however, and there has been a long-term decline in the quality of hedgerows and associated vegetation in England, the impacts of which are unknown.

Bank vole in detail

---

Bibliography

Atlas of the Mammals of Great Britain & Northern Ireland - by Multiple Contributors
Pelagic Publishing -- 2020 -- ISBN: 978-1784272043

Britain’s Mammals 2018: The Mammal Society’s Guide to their Population & Conservation Status - by Multiple Contributors
The Mammal Society -- 2020 -- ISBN: 978-0993567339

Collins Field Guide: Mammals of Britain and Europe - by David MacDonald and Priscilla Barrett
HarperCollins Publishers -- 1993 -- ISBN: 978-0002197793

Fauna Britannica - by Stefan Buczacki
Hamlyn Publishing -- 2002 -- ISBN: 978-0600598671

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 British Mammal Guide - by Steve Evans & Paul Wetton
Isabelline Films -- 2015 -- ISBN: N/A

The Encyclopaedia of Mammals - by David MacDonald (ed.)
Brown Reference Group -- 2006 -- ISBN: 978-0199206087

The New Amateur Naturalist - by Nick Baker
HarperCollins Publishers -- 2004 -- ISBN: 978-0007157310

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