146.

Gray-tailed Vole

Microtus canicaudus

French: Campagnol a queue grise / German: Grauschwanz-Wiihimaus / Spanish: Topillo de cola gris

Taxonomy. Microtus canicaudus G. S. Miller, 1897, McCoy, Willamette Valley, Polk County, Oregon, USA.

This species is monotypic.

Distribution. Clark County in SE Washington and Willamette Valley in NE Oregon, USA.

Descriptive notes. Head-body 108-123 mm, tail 32-45 mm, hindfoot 15-21 mm; weight greater than 50 g. Dorsum of the Gray-tailed Vole is yellowish brown or yellowish gray; venter and feet are grayish. Auditory bullae are inflated, and braincase is broad relative to length. Eyes are relatively large compared to most other species of Microtus . Tail is relatively short and gray and has dark dorsal stripe. Incisors are slightly procumbent, and incisive foramina are greater than 5 mm. Diploid numberis 2n = 24.

Habitat. Agriculturalfields, including grains, grass seed, pastures, hayfields, and fallow lands.

Food and Feeding. Gray-tailed Voles are thought to eat various grasses, clover ( Trifolium sp., Fabaceae), wild onion ( Allium sp., Amaryllidaceae), and false dandelion (Hypochaenris radicata, Asteraceae). They are frequently associated with agriculturalfields, especially fields grown for grass seed, small grains, and pasture lands.

Breeding. Breeding of Gray-tailed Voles probably occurs year-round. Adult females in reproductive condition have been found in March-December. Females have multiple litters each year, usually with 3-7 young (average 5). Gestation lasts 21-23 days. Captive females as young as 18 days old can mate and produce viable offspring.

Activity patterns. Gray-tailed Voles are terrestrial.

Movements, Home range and Social organization. Gray-tailed Voles construct underground burrows and complex tunnel networks, but they also use burrows of the Camas Pocket Gopher ( Thomomys bulbivorus). Densities fluctuate markedly, but few quantitative data are available. In enclosures, densities of 600 ind/ha have been attained. Owls, hawks, foxes, skunks, and domestic and feral cats are common predators.

Status and Conservation. Classified as Least Concern on The IUCN Red List.

Bibliography. Goertz (1964), Hall (1981), Hsu & Johnson (1970), Musser & Carleton (2005), Verts & Carraway (1987 1988), Wolff, Edge & Bentley (1994), Wolff, Schauber & Edge (1997).