47.

Western Red-backed Vole

Myodes californicus

French: Campagnol de Merriam / German: Westliche Rotelmaus / Spanish: Topillo rojo de California

Other common names: California Red-backed Vole

Taxonomy. Myodes californicus Merriam, 1890, Eureka, Humboldt County, California, USA.

Three subspecies are recognized.

Subspecies and Distribution.

M.c.californicusMerriam,1890—fromNOregonSalongthecoasttoNBayAreainCalifornia,USA.

M.c.mazamaMerriam,1897—EsideofCascadeRangeinOregonandCalifornia,USA.

M. c. obscurus Merriam, 1897 — C Oregon to NC California, USA.

Descriptive notes. Head-body 87-109 mm, tail 34-56 mm, hindfoot 17-21 mm, weight 15-40 g. The Western Red-backed Vole is larger than the Southern Redbacked Vole ( M. gapperi). Dorsum has chestnut-brown to reddish brown stripe, but it is paler and tail is more bicolored than on the Southern Red-backed Vole, with whiter belly. The Western Red-backed Vole can be distinguished from other sympatric voles by M? that have four loops of enamel on lingual side and reentrant angles on M, that do not exceed one-half width of tooth. Unlike species of Microtus, molars are rooted. Posterior margin of palate has thin triangular shelf that distinguishes the Western Red-backed Vole from the Southern Red-backed Vole. Diploid number is 2n = 56.

Habitat. Cool, moist microhabitats, particularly old fallen logs in mesic coniferous forests. Primary and secondary forests of coastal redwood ( Sequoia sempervirens, Cupressaceae); lodgepole pine ( Pinus contorta), Sitka spruce ( Picea sitchensis), Douglas fir ( Pseudotsuga menziesit), and western hemlock (7suga heterophylla), all Pinaceae; and western redcedar ( Thuja plicata, Cupressaceae) in western Oregon and northern California are prime habitats of the Western Red-backed Vole. Preferred habitat has high percentage of lichen cover, western hemlock canopy cover, more decaying logs, and less deciduous tree cover. At population highs, the Western Red-backed Vole also can be found in bearberry ( Arctostaphylos sp., Ericaceae) brushlands.

Food and Feeding. Hypogeous fungi (e.g. Rhizopogon sp., Gautieria sp.), in particular, form large portion of the diet of the Western Red-backed Vole, which plays a role in disseminating hypogeous spores and bacteria that may be critical to forest function. High-elevation populations tend to have more variable diets, including higher consumption of lichens.

Breeding. Western Red-backed Voles breed most often in February—October, but west of Cascade Range, breeding also has been documented all winter.

Activity patterns. Western Red-backed Voles stay active year-round and are mostly nocturnal. Mountain populations are active day and night.

Movements, Home range and Social organization. The Western Red-backed Vole uses log overhangs as runway corridors and cover to avoid predation. Average densities in coniferous forests are 1-2-7-9 ind/ha. Average home range was 4-6 ha for males and only 0-8 ha for females.

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

Bibliography. Alexander & Verts (1992), Bradley, Ammerman et al. (2014), Cassola (20161), Hall (1981), Maser et al. (1981), Musser & Carleton (2005), Tallmon & Mills (1994).