127.

Short-tailed Field Vole

Microtus agrestis

French: Campagnol agreste / German: Erdmaus / Spanish: Topillo agreste

Other common names: Field Vole, Short-tailed Vole

Taxonomy. Mus agrestis Linnaeus, 1761, Uppsala, Sweden.

Microtus agrestis is in the subgenus Agricola . In most phylogenetic reconstructions, it emerged as sister species to subgenus BlanJordimys with M. afghanus, M. bucharensis, and possibly M. juldasch:. Previously included lavernedii and rozianus as subspecies; two deeply divergent phylogenetic lineages now upgrated to species level. Monotypic.

Distribution. W, C & N Europe and N Asia, from the British Is and across C & E Europe (including the Carpathian Basin) and Fennoscandia to Siberia as far E as Lena River, S to NE Kazakhstan, N Mongolia, and extreme NW China (Altai and Barluk Mts in Xinjiang).

Descriptive notes. Head-body 92-132 mm, tail 30-53 mm; weight 22-72.5 g. Males are, on average, heavier (weight 35-4 g) than females (32-6 g). The Short-tailed Field Vole is of average size and proportions. Head is blunt, ears are short and hardly protruding from pelage, and eyes are small. Tail is ¢.36% of head—body length. There are six plantar pads, and females have four pairs of nipples, two pairs each of pectoral and inguinal. Fur is long, soft, and dense, with protruding long guard hairs. Dorsum is grayish brown, flanks are more buffy, and belly is gray. Back is sporadically washed buff or rusty. Tail is bicolored, well-haired, and tufted. Juveniles are grayer than adults. Various color variants are reported, occasionally piebalds, pale-coated, rarely albinos, and melanistic. Skull is deep and somewhat narrow, without much expansion of zygomatic arches. Braincase is long, bullae are proportionally large, and interorbital crest is low. Upper incisors are pronouncedly opisthodont. M* has distinct postero-lingualtriangle that is invariably isolated from alternation triangle on outer side. Similar additional triangle frequently occurs on M".

Habitat. Ungrazed grassland, fallow land, and clearfelled areas on wet ground with tufted hairgrass ( Deschampsia cespitosa) and purple moor-grass ( Molinia caerulea), both Poaceae, and sedges ( Carex, Cyperaceae) from sea level to elevations of c.2140 m. The Short-tailed Field Vole also occupies forest plantations, woodlands, moorland, Sphagnum (Sphagnaceae) bogs, dunes, and rocky habitats. In eastern Siberia, more than 50% of records are from coniferous or birch ( Betula, Betulaceae) woodlands.

Food and Feeding. Staple diet of the Short-tailed Field Vole is green leaves and stems of grasses and herbs, e.g. heat false brome ( Brachypodium pinnatum), dawny alpine oatgrass ( Avenula pubescens), tall oatgrass ( Arrhenatherum elatius), red fescue ( Festuca rubra), and creeping soft grass ( Holcus mollis), all Poaceae . Two dicotyledons are most preferred in Fennoscandia: clover ( Trifolium, Fabaceae) and dandelion ( Taraxacum, Asteraceae). Food variety is greatest in mid-summer; e.g. six plant species are eaten in May and 18 species in August in Fennoscandia. Short-tailed Field Voles also feed on grass seeds, roots, and mushrooms. Barking of trees occurs at high densities. Diet varies geographically and seasonally. Green plant material is most important in the west and was recorded in 80-100% of stomachs from taiga in north-eastern Russia. In eastern Siberia, green leaves and stems decrease in proportion (found in 44-7% of stomachs), and other items gain in importance: fruits and berries (179%), mushrooms (116%), and mosses (23-7%). Feeding is selective to maximize nutrient intake. High pressure for preferred food results in intense scramble-type competition in mid-summer, with important consequences on reproduction. In contrast, Short-tailed Field Voles tend to avoid certain plants (e.g. orchard grass, Dactylis glomerata, and tussock cottongrass, Eriophorum vaginatum, both Poaceae; and rush, Juncus, Juncaceae) and drastically reduce consumption of tufted hairgrass when it is acutely toxic to them. Daily food intake is 0-7 g per gram of body weight.

Breeding. Breeding season of the Short-tailed Field Vole is mainly in March-October, but reproduction can occur year-round. Reproduction intensity can be reduced in mid-summer when nutritional value of plants is low. Ovulation is spontaneous or induced, and it is facilitated by tactile, visual, and auditory stimuli. Gestation lasts 18-22 days (mean 20-8 days), and prenatal mortality is ¢.5% offertilized eggs. Numbers of embryos are 3-11/female, and litters are 1-8 young (mean range 4-7-5). Number of young depends on locality, season, and density. Northern litters can be larger than southern litters; e.g. mean numbers of embryos are 2-3-5 in Czech Republic vs. 3-:8-7-4 in Finland. Furthermore, winterlitters are smaller (3-2 embryos/ female) than summerlitters (5-7). Females have postpartum estrus and can deliver 4 litters/season. Young are born blind, deaf, and naked. They weight 2:2 g at birth and 12-5 g at 15 days old. Young nurse for 12-21 days. Females are sexually mature at c.4 weeks old. Early litters sexually mature and reproduce before their first winter; late-born young are mature in the following spring. Numbers of embryos are lower in young females (mean 5) than old females (6-8). Short-tailed Field Voles do not live longer than 20 months, and very few survive a second winter. Longest age in captivity was 39 months. Densities vary among years, either irregularly or following multiannual cycles.

Activity patterns. The Short-tailed Field Vole has an ultradian activity rhythm, with periods of 2-4 hours of feeding and peaks after sunset. Individuals are generally nocturnal in summer and diurnal in winter. The Short-tailed Field Vole does not depend on type of soil and digging possibilities. Therefore, aboveground runway systems are extensive and constructed through vegetation. Underground tunnels, where dug at all, are superficial, up to 20-30 cm deep, and rarely extensive. Nests are mainly on the ground’s surface in slight excavations of soil and under tussocks of grass or sedges. Globular nests are constructed of finely shredded grass and are c.20 cm in diameter.

Movements, Home range and Social organization. Short-tailed Field Voles are sedentary; they move over small areas (e.g. weekly c.150 m?). They seldom move more than 9-13-5 m. Postnatal dispersal is male-biased, and nearly one-quarter of young females stay within natal home ranges even after dispersal. Movements more than 1 km can be overland or by swimming but are rare. In some areas, Short-tailed Field Voles move seasonally between open grassland and forest edges. Home ranges are larger during breeding season (1434 m® for males and 773 m? for females) than non-breeding season (600 m? for males and 400 m? for females). Pregnant females have larger home ranges than non-pregnant females. Female home ranges are smallest during lactation. Home rangesare significantly smaller at high densities. Outside breeding season, home ranges overlap, but reproductive females are territorial. Spacing is maintained by mutual avoidance. Reproductively active males are also territorial. Breeding system is promiscuous, with up to one-third oflitters sired by multiple fathers. Males with larger home ranges sire more offspring, but they do not attempt to monopolize mating access to breeding females. Adults emit ultrasonic calls (20-80 kHz, mean 35-40 kHz) during a variety of heterosexual encounters.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Shorttailed Field Vole is widespread and common in many parts ofits distribution (e.g. prebreeding UK population is estimated at 75 million individuals). It is rare in some parts of its distribution, particularly along its periphery in eastern Siberia.

Bibliography. Anufriev (1994b), Bauer (2001b), Krapp & Niethammer (1982), Lambin (2008), Mandelli & Sales (1997), Paupério et al. (2012), Revin (1989), Shenbrot & Krasnov (2005), Sludskiy et al. (1978), Tavrovskiy et al. (1971).