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Japanese Grass Vole

Alexandromys montebelli

French: Campagnol de Montebello / German: Japanische Wiihimaus / Spanish: Topillo de Japon

Taxonomy. Arvicola montebelli Milne-Edwards, 1872, Fusiyama [= Mount Fuji], Honsu Island, Japan.

Alexandromys montebelli 1s closely related to A. oeconomus and A. kikuchii, which 1s also evident from pattern of pairing of sex chromosomes. Monotypic.

Distribution. Endemic to Japan on Honshu, Kyushu, Sado, and Noto-jima Is.

Descriptive notes. Head-body 95-136 mm, tail 29-50 mm; weight 22-62 g.

Individuals in southern populations are larger than individuals in northern populations; therefore, pattern of size variation is contrary to Bergmann’s response. Japanese Grass Vole is medium-sized, with tail ¢.36% of head-body length. Eyes are small, and relatively large circular ears overtop pelage. Females have four pairs of nipples, two pairs each of pectoral and inguinal. There are five (rarely six) plantar pads. Dorsum is dark brown, shaded buff in some individuals, and belly is gray. Flanks are lighter, and demarcation is distinct. Tail is blurrily bicolored. Skull is of normal proportions, and greatest width across zygomatic arches is 57% of cranial length. Braincase is long, bullae are fairly large, and rostrum is short. Temporal ridges merge and form low interorbital crest. Upper incisors are heavy and orthodont. M” normally has four inner and three outer salient angles; posterior loop is decidedly short. Anteroconid complex of M' is simple. Other molars show no peculiarities.

Habitat. Meadows, pastures, forest plantations, and cultivation, regardless of elevations. Japanese Grass Voles are also reported in natural forests. Recent degradation of pristine forests has enabled expansion ofJapanese Grass Voles into higher elevations.

Food and Feeding. Japanese Grass Voles eat plants but occasionally prey on gastropods and larvae of grasshoppers and butterflies. Plants identified in diets ofJapanese Grass Voles are from 38 families, including daisies ( Asteraceae), cucurbits ( Cucurbitaceae), honeysuckle ( Caprifoliaceae), mallow ( Malvaceae), mint ( Lamiaceae), nightshades ( Solanaceae), primroses ( Primulaceae), euphorbias ( Euphorbiaceae), legumes ( Fabaceae), mustard ( Brassicaceae), buckwheat ( Polygonaceae), nettle ( Urticaceae), plantain ( Plantaginaceae), sedges ( Cyperaceae), grasses ( Poaceae), and puzzlegrasses ( Equisetaceae). In one study south of Tokyo, green plant material was a staple food throughout the year, and animals were entirely absent in diets. Seven plant species were found: birdeye speedwell ( Veronica persica, Plantaginaceae), creeping woodsorrel ( Oxalis corniculata, Oxalidaceae), common chickweed ( Stellaria media, Caryophyllaceae), Japanese dock ( Rumex japonicus, Polygonaceae), dwarf Japanese euonymus (Euonymusjaponicus, Celastraceae), and two fleabanes ( Erigeron sumatrensis and E. philadelphicus, Asteraceae).

Breeding. Breeding season of the Japanese Grass Vole occurs in spring and autumn. Smallest weight of pregnant female was 22-6 g. Females are polyestrous; gestation is 21 days. Numbers of embryos are 2-9/female (mean range 4-3-5-1), depending on locality and season. Females show postpartum estrus on the day of parturition; therefore, lactation does not interrupt implantation. Intervals between successive litters are 20-21 days (minimum 18 days). Young are born naked, blind, and deaf, and they weigh 2-3-4 g. Mean weights in small and large litters are 2-7 and 2-4 g at birth, 18-2 and 16-7 g at weaning at 20 days old, and 34-9 and 28-8 g at 60 days old, respectively. Infant mortality was low under laboratory conditions. Males grow faster than females. Life expectancy in captivity is 783 days for females and 825 days for males.

Activity patterns. Diurnal activity of the Japanese Grass Vole under standard captive conditions is polyphasic with several peaks. Free-living individuals are mainly nocturnal from spring to autumn and diurnal in winter. The Japanese Grass Vole digs underground burrows with tunnels of 3-4 cm in diameter. Nests are woven from leaf fibers of wheat, rice, shortawn foxtail ( Alopecurus aequalis), annual meadow grass ( Poa annua), and blady grass ( Imperata cylindrica), all Poaceae; speedwell ( Veronica didyma, Plantaginaceae), shepherd’s-purse ( Capsella bursa-pastoris, Brassicaceae), and umbrella sedge ( Cyperus iria, Cyperaceae).

Movements, Home range and Social organization. At 50 ind/ha, home ranges ofJapanese Grass Vole have maximum length of 25 m for females and 30 m for males (overall mean 16-1 m). Home ranges were stable in 56% ofJapanese Grass Voles studied.

Status and Conservation. Classified as Least Concern on The IUCN Red List (as Microtus montebellr).

Bibliography. Borodin et al. (1997), Iwasa (2015b), Kaneko (1978, 1988), Nakatsu (1975, 1977), Obara (1970), Urayama (1996).