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Bank Vole

Mpyodes glareolus

French: Campagnol rousséatre / German: Rotelmaus / Spanish: Topillo rojo

Taxonomy. Mus glareolus Schreber, 1780, Island of Lolland, Denmark.

Throughout the 20" century, glareolus was included in FEvotomys or Clethrionomys; both generic names are junior synonyms of Myodes . Myodes glareolus is more closely related to M. centralis and M. macrotis than to M. rutilus . Past and present hybridization with M. rutilus was documented in the zone of sympatry, and all individuals with alien mitochondrial genome are M. glareolus . Large number of subspecific names was proposed for M. glareolus, but they were never revised. Some sources list 26 subspecies in western Europe alone, while others recognized 10-13 subspecies from the entire distribution. Phylogeographic studies using molecular markers retrieved complex evolutionary history and survival in multiple glacial refugia. Monotypic.

Distribution. W Europe from Atlantic coast E to Yenisei River, N border set by Arctic tundra and S border frequently coincides with mountain ranges: Pyrenees, Alps, Apennines, and Balkan in S Europe, Pontic Mts in Anatolia, and Altai and Sayan Mts in C Asia; widespread on islands offshore Atlantic and Baltic coasts. Introduced to SW Ireland.

Descriptive notes. Head-body 80-135 mm, tail 32-72 mm; weight 12-61 g. Sexes of Bank Voles are similarly sized. Size varies geographically and seasonally. They tend to be small in central and eastern parts of the distribution, and they are large in European mountains and northern European Russia and on some islands off Great Britain. The Bank Vole is slender, with large semicircular ears and relatively long tail ¢.50% of head-body length. Females have four pairs of nipples, and there are six plantar pads. Pelage is soft, and denser in winter (204 hairs/mm?) than summer (134 hairs/ mm?). Back is rusty, flanks are gray, and belly is light gray, occasionally washed buff. Contrast between back and flank pelage is obvious, particularly in adults. Juveniles are darker and less rusty. Various color variants have been reported (black, tan, yellow, and white), but they are rare in the wild. Skull is delicate, with moderately expanded zygomatic arches and weak mandible. Braincase and interorbital region have weak ridges that become more prominent with advanced age. Posterior edge of hard palate ends abruptly as a shelf. Molars develop roots that continue to grow so their length correlates with age. Enamelis thin, reentrant angles are partly filled by cement, and salient angles are rounded.

Habitat. Mature deciduous, mixed, and coniferous forests, with thick ground cover and mesic conditions from sea level to tree line at elevations of 1900-2350 m. Bank Voles also occupy shrublands, bogs, abandoned fields, hedgerows, and stands of dwarf pine ( Pinus mugo, Pinaceae). In lowlands, they occupy a broad transitional zone between forests and steppe.

Food and Feeding. Bank Voles are mostly herbivorous, with green plants and seeds forming majority in the diet, at least in deciduous and mixed forests. In boreal forests, they compensate for shortage of seeds by eating berries, lichens, and mushrooms. Fungi, roots, dead leaves, flowers, grasses, and mosses are consumed but are of minor importance. In European Russia, Bank Voles feed on ¢.280 species of herbal plants, 230 species of trees and shrubs, and 10-15 species of lichens and mosses. Animal food is of secondary importance (less than 5% of the diet), but diverse nevertheless, including annelids, gastropods, opiliones, spiders, and representatives of at least ten major insect orders, including beetles, butterflies, and dipterans. Daily requirements in summer are 0-69 g of food per gram of body mass. Bank Voles cache food and carry seeds in false cheek pouches.

Breeding. Breeding season of Bank Voles lasts from March-April until September-October, but there is lot of variation involved. Populations at northern latitudes and high elevations have shorter and more intense breeding seasons. Abundant seed mast can extend reproduction throughout winter, and high densities can suppress breeding. Normally, breeding season lasts seven months in central Europe, five months in Finland, and 3-3-5 months in southern European mountains. Sexual maturity in males is triggered by longer photoperiod in spring. Testes of 100 mg normally contain spermatozoa, and males can sire multiple litters. Females do not have estrous cycles, and ovulation is induced by proximity of males or mating. Gestation last 18-20 days (mean 19-6 days). Numbers of embryos are 1-13 (overall species mean 4-8). There is south-tonorth cline in litter size, with larger mean counts of embryos in Siberia (5-8) and European taiga (5-8) than in southern Europe (4-5) and western Europe (4-8). Winter litters are smaller, with an average of 3-3-6 embryos. Litters of primiparous females are smaller than those of multiparous females. Postpartum females are highly fertile, and successive litters can be produced every 3—4 weeks. Young are born naked and blind, with toes fused, teeth unerupted, and ears sealed. Initial weight of c.2 g increases to 9-10 g on day 18 when young start weaning. Lactation lasts 17-18 days. During the first month, young gain 0-4-0-5 g/ day . Fur and incisors emerge toward the end of the first week, ears and eyes open on day 12-13, and young start taking solid food by day 15. They start breeding at 1-5-2 months for females and c.2 months for males. Mortality is high (c.60%) during first six weeks of life. Life expectancy is 18-21 months, and survival of second winter is exceptional. Captive Bank Voles can live up to 40 months.

Activity patterns. Bank Voles are active throughout the year. Circadian activity is polyphasic and normally peaks at dusk and dawn. They are most nocturnal in summer. Adult females normally maintain 2-3 nests under logs or stones, or in the ground. Nests are constructed with grasses and leaves and are 10-15 cm in diameter. Bank Voles also have several caches. They are more agile on the ground than most arvicolines (e.g. Microtus) and can jump and climb well.

Movements, Home range and Social organization. Bank Voles mainly move by walking and running. Most activity is at the ground level, but they climb and are good diggers.

Dispersal is male-biased, and females have more site fidelity. Home ranges in Great Britain vary widely from 261 m? to 2208 m®. Size of home range depends on season, habitat conditions, resource availability, sex, age, social status, and population context. Home ranges are larger for males (1000-8000 m?) than females (200-1000 m?) and larger in summer than winter. Home ranges of both sexes overlap during the non-breeding season. During the breeding season, females maintain exclusive home ranges. Male home ranges continue to overlap and extend over home ranges of several females. Females defend home ranges, most vigorously during pregnancy and lactation. Adults usually do not fightjuveniles. Bank Voles communicate through chemical signals and vocalization. Adults emit calls of various frequencies and are most vocal during aggressive encounters and mating. Sexually experienced males are more vocal than inexperienced males. Young emit ultrasonic calls, and their intensity and rate relate to cold stress. Scent marking is important in spatial behavior in both sexes and is also used in recognition among individuals.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Overall distribution of the Bank Voleis ¢.8,700,000 km?.

Bibliography. Abramson, Lebedev, Bannikova & Tesakov (2009), Anufriev (1994a), Bashenina (1981), Gromov & Erbajeva (1995), Kotlik et al. (2006), Melnikova et al. (2012), Mironov (2016b), Petrusewicz (1983), Shenbrot & Krasnov (2005), Shore & Hare (2008), Viro & Niethammer (1982).