176.

Altai Vole

Microtus obscurus

French: Campagnol obscur / German: Studostfeldmaus / Spanish: Topillo de Altai

Other common names: Dark Vole

Taxonomy. Hypudaeus obscurus Eversmann, 1841, probably near Chujskij trakt (a road), Altai Mtns., Russia.

Microtus obscurus is in subgenus Microtus and arvalis species group. It is frequently regarded as a semi-species, subspecies, or group of populations of M. arvalis . There is no consensus on number of subspecies | of M. obscurus . Phylogeographic studies retrieved main evolutionary divergence on the Caucasus. Monotypic.

Distribution. E Ukraine and Crimea, C, E & S European Russia, Georgia, E Turkey, Armenia, Azerbaijan, extreme NW Iran, N & E Kazakhstan, S Siberia (as far E as Tomsk and Kemerovo regions, and W Tuva), NW Mongolia, and NW China (Xinjiang).

Descriptive notes. Head-body 101-136 mm,tail 32-51 mm; weight 23-48 g. In external and craniodental morphology, the Altai Vole is nearly identical to the Common Vole ( M. arvalis). Tail is 28-3-40-6% of head—body length. Females have four pairs of nipples. Most individuals are dark brown on back, rarely yellowish brown or brownish buff, but flanks are more buff. Belly is gray and washed yellow. Skull is widely arched, with width across zygomatic arches accounting for ¢.56% of skull length. Sagittal crest is evident but low, and interorbital region is constricted in adults. Teeth are like those in the Common Vole.

Habitat. Short grass meadows and arable lands from lowlands to mountain pastures at elevations up to ¢.3000 m. In central Asia, Altai Voles occupy semi-deserts, steppe, and forest steppe.

Food and Feeding. The Altai Vole mainly depends on green leaves and stalks (79-100% of diet). Dietary contents depend on a season. In June, diets contain dandelion ( Taraxacum) and sagebrush ( Artemisia austriaca), both Asteraceae; clover ( Trifolium, Fabaceae); bluegrass ( Poa pratensis, Poaceae); purple-flowered garlic ( Allium rotundifolium, Amaryllidaceae); and tulip (7ulipa, Liliaceae). In August, the Altai Vole mainly eats fescue ( Festuca sulcata), feather grass ( Stipa capillata), and crested hair-grass ( Koeleria gracilis), all Poaceae, and sagebrush ( Artemisia austriaca). Seeds are eaten in summer and autumn. In late autumn, proportion of seeds becomes more important (up to 25% of diets), but it can be much higher (79%) in grain fields. Altai Voles store food in underground caches. During the growing season, small amounts of green plant parts are stored, such as Asian forget-me-not ( Myosotis suaveolens, Boraginaceae), lady’s mantle ( Alchemilla, Rosaceae), knotweed ( Alopecurus soongaricus, Poaceae), bishop’s goutweed ( Aegopodium podagraria, Apiaceae), and cleavers (Gallium, Rubiaceae). In spring, caches in Kazakhstan contained 70-91 bulbs of saffron (Crocus, Iridaceae), weighing 75-110 g.

Breeding. Breeding season of the Altai Vole occurs year-round but can be interrupted by summer droughts in arid zones and by winter at high elevations. Reproductively active individuals weigh 12-5-34 g (individuals of the same year) and 38-42 g (overwintered). Females have 1-11 embryos, usually 4-6. Mean number varies between months. In northern Kazakhstan, highest counts are in April (mean 6-2), May (7-3), and June (6-3). Females usually have 3—4 litters/season. Resorption of embryosis lower in steppe regions of Kazakhstan (31%) than in semi-deserts (8-2%). Resorption rates steadily increase from spring (5-9%) to autumn (28:6%). Young are born naked, blind, and deaf. They start emerging outside burrows when they weigh 6 g.

Activity patterns. Diurnal activity of the Altai Vole is polyphasic. It excavates burrow system of c¢.6 m in length, with 3-8 entrances and 1-2 nest chambers. Tunnels are mainly 5-15 cm deep. Nest chamber (dimensions 15-18 x 10-12 cm) has 1-3 exits and is 20-25 cm deep. Burrows in arid zones are simpler and descend 35 cm. Temporary shelters with simple tunnels 10-15 cm long are scattered at distances of 3-5 m around burrows. Altai Voles also construct nests under coils of hay, stones, and snow, and even on the ground’s surface. Such nests are usually 20-25 cm in diameter and are of diverse construction. Altai Voles occasionally inhabit abandoned burrows of ground squirrels ( Spermophilus, Sciuridae).

Movements, Home range and Social organization. Altai Voles lives in family groups. Expansion of a family from spring onward is followed by expansion of burrow system that can reach diameters of 15-20 m in autumn. Altai Voles are mainly active 15-30 m around burrows but can move up to 1000-1200 m away. During snow melt, they might leave their burrows and find temporary shelters under hay coils or stones. Altai Voles are rarely preyed on.

Status and Conservation. Classified as Least Concern on The [UCN Red List (as Microtus arvalis, that is, together with the Common Vole). Within its distribution, the Altai Vole is one of the most common rodents; therefore, taxonomic split from the Common Vole probably did not alter conservation status of either species.

Bibliography. Krystufek & Vohralik (2005), Lavrenchenko et al. (2009), Mahmoudi et al. (2017), Sludskiy et al. (1978), Tougard et al. (2013).