171.

Social Vole

Microtus socialis

French: Campagnol social / German: Gesellige Wihimaus / Spanish: Topillo social

Taxonomy. Mus socialis Pallas, 1773, probably Gur’evsk Oblast (= Gur’ev District) between the Volga and Ural rivers, Kazakhstan.

Microtus socialis is in subgenus Sumeriomys and socialis species group. In the past, it was synonymized with rani, guentheri, hartingi, paradoxus, schidlovski, and mustersi . Diploid number of 62 delimits M. socialis from all “social voles” except M. paradoxus . Taxonomic and geographical scopes are still loosely defined in south-western Asia, and subspecies are tentative. Widely used subspecific name Ayrcana has been changed for gender agreement. Eleven subspecies recognized.

Subspecies and Distribution.

M.s.socialisPallas,1773—SEuropeanRussia(VolgogradandAstrakhanregionsandKalmykia)andWKazakhstan.

M.s.aristoviGolenishchev,2002—E&SArmeniaandSAzerbaijan(includingNakhichevan).

M.s.astrachanensisErxleben,1777—SEuropeanRussia.

M.s.binominatusEllerman,1941—C&EGeorgia,NWArmenia,andNWAzerbaijan.

M.s.bogdoensisWangFenggui&MaYong,1981—NWChina(CXinjiang).

M.s.goriensisArgyropulo,1935—ETurkey.

M.s.gravesiGoodwin,1934—C&EKazakhstan,NKyrgyzstan,NWTajikistan,andNWChina(extremeNWXinjang).

M.s.hyrcanusGoodwin,1940—NW&NIran.

M.s.nikolajeviOgnev,1950—UkraineandCrimea.

M.s.parvusSatunin,1901—NCaucasus(RussiaandprobablyextremeNEAzerbaijan).

M. s. zaitsevi Golenishchev, 2002 — E Azerbaijan.

Descriptive notes. Head-body 93-116 mm, tail 24-37 mm; weight 20-38 g. Male Social Voles are larger than females. Mean weight of nominate subspecies is 33-7 g (males) and 27-3 g (females). Size varies geographically from small (head-body 89-95 mm) in subspecies socialis and nikolajevi to large (head-body 95-115 mm) in subspecies binominatus and bogdoensis. The Social Vole is small, with a relatively long tail that varies among subspecies from ¢.20-7% of head-body length in gravesi to ¢.28:2% in binominatus. Ears are relatively long and protrude from fur, and eyes are large. There are five plantar pads. Females have four pairs of nipples, two pairs of pectoral and two pairs of inguinal. Fur is soft, short, and lacks coarse guard hairs. Dorsum is grayish buffy, frequently shaded rusty, and venteris light gray. Skull has large but low braincase and pronouncedly swollen bullae. Interorbital region is wide. Dentition is as in the Anatolian Vole ( M. anatolicus).

Habitat. Open grassy habitats on chernozem (black-colored, humus-rich soil), clay, sand, and even saline soils; steppes with various grasses and sagebrush pastures, semideserts, fallow land, winter cereals, alfalfa fields, and vineyards up to elevations of 2000 m. In arid habitats, Social Voles concentrate in spots of higher soil moisture. Exceptionally (e.g. in Tajikistan), they occur in juniper ( Juniperus, Cupressaceae) woodland with herbaceous and grassy understory.

Food and Feeding. Seeds/cereals always constitute at least 30% of diet of the Social Vole, with a similar proportion of green plants; insects and mollusks are also eaten. About 100-150 species of plants have been recorded in the diet, and this varies by locality from a low nine species to heights of 60-65 species. In spots with low plant diversity, Social Voles feed on species that are otherwise rejected. Besides seeds/cereals, the most important plants are wild grasses ( Poaceae), legumes ( Fabaceae), daisy plants ( Asteraceae), mint plants ( Lamiaceae), and goosefoot plants ( Chenopodiaceae). The most frequently eaten are couch grass ( Agropyron cristatum), false wheatgrasses ( Eremopyrum orientale, E. triticeum), barbed goatgrass ( Aegilops squarrosa), purple lovegrass ( Eragrostis minor), junegrasses ( Koeleria gracilis, K. caucasica), bluegrass ( Poa bulbosa), chicory ( Cichorium intybus), common yarrow ( Achillea millefolium), common dandelion ( Taraxacum officinale), warmwood ( Artemisia), burdock ( Cousinia eryngioides), various species of clovers ( Trifolium and Medicago), forage kochia (Kochia prostrata), different thistles ( Salsola rigida, S. ruthenica, S. dendroides), and goosefoot ( Chenopodium). Green plants are most important in spring, seeds in autumn, and roots, bulbs and tubers in winter. Daily intake is equivalent to ¢.75% of body weight. Full stomachs weigh 1-5-3 g. Social Voles make caches of 250-1200 g of plant material, exceptionally up to 3 kg.

Breeding. Social Voles breed throughout the year in the Caucasus, with decline in December—January. Breeding season is shorter in Crimea (March-November), with decline in June-July. Ovulation is induced. There are 2-3 liters/season in Kalmykia and 3-5 litters in Crimea. Gestation lasts 21-22 days. Females have 1-11 embryos; means vary geographically from 4-5 (S Kazakhstan) to 7-4 (Azerbaijan), and differ ences might be genetically determined. Means for spring and autumn litters of captive Social Voles are 3-9 and 3-1 for subspecies goriensis and 4-5 and 4 in the nominate subspecies. Captive litters are also smaller than wild ones, with means of 3-1-4. Multiparous females have, on average, larger litters than primiparous females. Although postpartum estrus is possible, females normally copulate when lactation ends. Successive litters are 40-47 days apart. Embryonic mortality in the wild is 0-10% (mean 5%). Newborns are nude and blind and have sealed ears; they weigh 2-2 g. Until weaning, they gain 0-54 g/ day . Eyes open at 10-12 days old. Young start eating solid food at c.2 weeks old. Postnatal molt starts at 25 days old and ends at 60 days old.

Activity patterns. Social Voles excavate burrows on their own or occupy tunnels dug by mole voles ( Ellobius), jirds ( Meriones, Muridae), or sousliks ( Spermophilus, Sciuridae). Digging is most active in spring, late summer, and early autumn, but it goes on year-round. A family burrow system has 6-35 holes spaced 0-5-3 m apart. Entrances are connected with 3-5cm wide pathways that are usually 20-60 cm long (up to 106 cm). Burrows in arable land are usually of simpler structure. Total length of tunnels per burrow system is usually up to 6 m. Tunnels are 3-30 cm below surface. There are 1-5 chambers in each family burrow system. Nest chamber has 1-3 exits and contains a spherical nest 11-16 cm in diameter and weighing up to 29-5 g. Nest is woven of soft plant material and has 2-5cm thick wall. Nest chamberis usually 30-50 cm deep and at least 1-5 m (up to 4 m) from a surface entrance. Caches are smaller than the nesting chamber, with diameters of 6-10 cm. Scattered around are short (5-10 cm) and simple temporary burrows. Underground galleries protect Social Voles against adverse environment. Temperature inside tunnels is ¢.20°C in spring, 27-31°C in summer, and 5-8°C in late October when freezing starts aboveground. Social Voles change depths of nesting accordingly: 24-4 cm deep in May-June, 30-5 cm in July, 26-2 cm in September, and 31-7 cm in winter. Social Voles are philopatric, using the same burrow system regardless of season. Melting snow in spring can force individuals to move up to 200-300 m. Burrows are defended and are used by succeeding generations.

Movements, Home range and Social organization. Social Voles live in small family units with a breeding pair and 1-2 litters. A family burrow system extends 6-4-160 m* and can be displaced in the event of excessive droughts, heavy rains, and fires. Social Voles move to a new site during the night. More than 50% of breeding voles are monogamous. Males can control two females that maintain own home ranges. Pair stability is a precondition for breeding; formation of pairs is initiated by increased mobility of males. Young males frequently excavate burrows notfar from their natal dens and associate with homeless females.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Distribution of the Social Vole is fragmented, and some of the isolated, endemic subspecies (astrachanensis, gorensis, nikolajevi, parvus) might be under threat. Diets of Social Voles have become less diverse in regions that are affected by overgrazing, increased aridity and habitat degradation in mid-20™ century.

Bibliography. Gromov & Erbajeva (1995), Krystufek & Vohralik (2005), Shenbrot & Krasnov (2005), Zima et al. (2013), Zorenko (2013), Zorenko & Golenishchev (2016a).