52.

Northern Red-backed Vole

Myodes rutilus

French: Campagnol boréal / German: Polarrételmaus / Spanish: Topillo rojo septentrional

Other common names: Red ole

Taxonomy. Mus rutilus Pallas, 1779, center of Ob River delta, Siberia, Russia.

In the past, M. rutilus was included in Evotomys or Clethrionomys; both generic names are junior synonyms of Mpyodes. Present and past hybridization was documented in zone of sympatry with M. glareolus and in parapatric zone with M. gapperi . A number of subspecies have been recognized on both sides of Beringia, and their validity has been questioned with traditional subspecific systematics. Molecular reconstructions retrieved three divergent allopatric lineages with zones of secondary contact between them. These lineages diverged more than 100,000 years ago. Beringian lineage encompasses all populations in North America, Kamchatka, Sakhalin, and Hokkaido. Remaining Palearctic populations are in two lineages, separated by the Yenisei River. Monotypic.

Distribution. From N & E Fennoscandia E across N European Russia and Siberia to Kamchatka, Sakhalin, Hokkaido, some Beringian Is (Unimak and St. Lawrence), Alaska, and N Canada; in the N it follows Siberian rivers to reach the shores of the Arctic Ocean, and in the S the range embraces N Kazakhstan, N Mongolia, N China (Xinjiang, Inner Mongolia [= Nei Mongol], Heilongjiang, and Jilin), and N North Korea. Introduced to Bering and Medny Is, offshore Kamchatka.

Descriptive notes. Head-body 85-123 mm,tail 21-50 mm; weight 14-5-50 g. Females have four pairs of nipples. The Northern Red-backed Vole is very similar to the Bank Vole ( M. glareolus). Bright reddish-brown dorsal pelage is frequently and clearly demarcated from grayish flanks. Winter pelage is brighter and denser, with 18-9 mg of hair/cm? vs. 10-6 mg of hair/cm? in summer. Tail is distinctly bicolored, ¢.33% of head-body length (shorter than the Bank Vole’s), and densely covered with hair; it has a long pencil. Albinos and melanistic individuals have been captured in the wild. Skull retains juvenile shape and hence is less ridged than the Bank Vole’s skull. Molars develop roots at 5-6 months old (much later than in The Bank Vole). M? is always complex, with four inner salient angles.

Habitat. Taiga and continental tundra, with broad habitat tolerance and recorded up to elevations of 2300 m in the Altai Mountains. In taiga, Northern Red-backed Voles occurin virtually all successional stages of spruce ( Picea), Siberian pine ( Pinus sibirica), and fir ( Abies sibirica), all Pinaceae; aspen ( Populus tremuloides) and willow ( Salix), both Salicaceae; alder ( Alnus) and birch ( Betula), both Betulaceae; and various shrubby habitats with Vaccinium and Empetrum (both Ericaceae) and Cornus (Cornaceae) . In tundra, they occur in northern shrub vegetation, open larch ( Larix, Pinaceae) woodland, rocky fields, and talus slopes. Mosses ( Pleurozium, Hylocomium, and Sphagnum), hypogeous fungi (Endogone), and lichens (Cladonia and Peltigera) are important habitat components. Northern Red-backed Voles prefer sites with dense ground cover that provide protection from weather and predators. Across Siberia, they regularly enter buildings and can reproduce inside of them throughout the year; winter invasions of houses are reported in Europe and North America.

Food and Feeding. The Northern Red-backed Vole is generalist and eats leaves, buds, twigs, berries of shrubs, forbs, fungi, mosses, lichens, and occasionally insects. Summer diet in Alaska contains berries, fungi, and lichens, rather than succulent green plants, and seeds can be important elsewhere (e.g. in Fennoscandia). Hypogeous fungi are consumed in all seasons but are particularly important in spring when they help to increase body weight. In North America, Northern Red-backed Voles eat berries in autumn and winter, lichens in winter and spring, and mosses in summer. Proportion of insects declines as summer progresses. In Siberia, berries dominate in spring and summer, mushrooms can prevail in autumn; and lichens are important in spring and summer. Siberian pine nuts are the single most important food in autumn and winter in the Altai Mountains. Northern populations store food in summer and autumn for use in winter.

Breeding. Northern Red-backed Voles are promiscuous. Breeding season extends from beginning of April until mid-September. It is longest in taiga of southern Siberia (5-5-5 months), shortest in tundra of north-eastern Siberia (c.3 months), and intermediate in Yakutia (= Sakha Republic) taiga (4-4-5 months). Breeding can start under snow but usually coincides with snowmelt. Weights of ovaries peak in May and decline steadily afterward; uteran weights are constantly high in April-July. Winter reproduction depends on food availability and quality and is unusual in northern populations. Females are polyestrous and produce up to fourlitters (usually 2-3 litters) during the breeding season. Adult females have morelitters than young females that matured in their first year. Usually ¢.20% of females start reproducing in the year they were born. Gestation lasts 17-19 days, and first litters are usually produced in late May or early June. Numbers of embryos per female are 2-14, and means do not vary much among regions: 4-:8-7-3 in Finland, 5-8-7-9 in Siberia, 5-4-7-3 in the Altai-Sayan Mountains, 4.7-8-5 in north-eastern Russian Far East, and 5-7-6-2 in Alaska. Northern litters tend to be larger. Resorption of embryosis low and accounts for 0-6-3-4% embryotic mortality in Siberia. Young are born naked, deaf, and blind. Hair emerges at 4-7 days old, eyes open at eleven days, and young start taking solid food at 13 days. Young are weaned and leave their nests at 15-18 days old when they are able to regulate their body temperatures. Average daily weight gain during first 20 days is c.0-5 g. At low density, young start reproducing in the year of birth. Lifespan is 10-12 months. Populations oscillate with peak densities every 3-5 years.

Activity patterns. Circadian rhythm of the Northern Red-backed Vole is mainly nocturnal and crepuscular in spring and polyphasic in winter. Daily peaks of activity are also longerin spring than winter. Established breeding populations are sedentary, and females are more philopatric than males. Females also stay longer in nests and devote more time to grooming young. Surface runways constructed by species of Microtus through vegetation are used as travel corridors by Northern Red-backed Voles. In winter, they construct long tunnels under snow. Summer nests are built underground, in dead wood, or under rocks or roots, and winter nests are built among thick mosses under snow. Nests are constructed of dry leaves and stalks and are 9-20 cm in diameter. Northern Red-backed Voles readily climb trees up to 2 m aboveground and descend head first.

Movements, Home range and Social organization. Adult Northern Red-backed Voles move 370-390 m away from their nests, and distances can be up to 1 km for males. At temperatures as low as 40°C to =50°C, individuals can move 70-80 m across snow. They leave degraded (e.g. burned) habitat in favor of nearby unaffected habitat. Home ranges are larger for males than females, larger during reproductive season than winter, and larger in tundra than taiga. Geographical variation in home range size may reflect differences in resources. Home ranges of immatures are 0-1-0-5 ha in summer and 0-04-0-1 ha in winter. Female home ranges in Finland were 0-42-0-65 ha, and male home ranges in Russia were 1-5-1-8 ha. Females are territorial. Northern Red-backed Voles are mostly solitary or live in small groups and share communal nests in autumn and winter.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Northern Red-backed Vole is one of the few arvicolines with Holarctic distribution that encompasses c.18,500,000 km?.

Bibliography. Bobretsov (2009), Gromov (2009), Gromov & Erbajeva (1995), Henttonen & Peiponen (1982), Kohli et al. (2015), Krivosheev (1984), Nations & Olson (2015), Runck et al. (2009), Shenbrot & Krasnov (2005), Stevenson et al. (2009), Tavrovskiy et al. (1971), Yudin et al. (1979).