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Red Tree Vole

Arborimus longicaudus

French: Phénacomys arboricole / German: Rote Baumwi (ihimaus / Spanish: Topillo arboreo rojo

Other common names: Reddish Tree Mouse

Taxonomy. Phenacomys longicaudus True, 1890, “Marshfield, Coos County, Oregon.”

Two subspecies are recognized.

Subspecies and Distribution.

A.l.longicaudusTrue,1890—WCascadeRangefromNOregonStoHumboldtCountyinNWCalifornia,NWUSA.

A. l. silvicola A. B. Howell, 1921 — NW Oregon coast, S of Clatsop County, USA.

Descriptive notes. Head-body 98-104 mm, tail 60-83 mm, hindfoot 19-22 mm; weight 25-50 g. The Red Tree Vole is relatively small, and females generally average larger than males. Pelage is reddish dorsally and lacks distinct stripe; belly is washed with reddish orange hairs. Tail is relatively long (more than 50% of head-body length) and indistinctly bicolored. Lower molars distinguish it from other sympatric vole species. On labial side, reentrant angles of lower molars extend two-thirds the way to lingual side, while reentrant angles on lingual side extend only one-third the way to labial side. Skull has distinct longitudinal depression between orbits, bordered by pronounced ridge, highly recurved incisors, and relatively wide incisive foramina. Diploid number of most populations is 2n = 54. One southern Oregon (USA) specimen had 2n = 48, and further study of karyotypic variation in these populations is needed.

Habitat. Mesic old growth forests of Douglas fir ( Pseudotsuga menziesii), grand fir ( Abies grandis), Sitka spruce ( Picea sitchensis), or western hemlock ( Tsuga heterophylla), all Pinaceae, up to elevations of ¢.1600 m. Red Tree Voles can be found in older second growth forests. They are uncommon or absent in young or managed timber stands but prefer lower elevation forests with high canopy cover, high stump density, and low snag density.

Food and Feeding. Red Tree Voles are distinctive from other voles, except their sister species, the Sonoma Tree Vole (A. pomo), because they feed primarily on needles of Douglasfir. They also eat needles and occasionally bark on twigs of other conifer trees. They apparently obtain water from accumulated dew and fog on plants.

Breeding. Red Tree Voles breed in most months of the year, but mostlitters are born in February-September. Females can breed within 24 hours of giving birth. Gestation is ¢.28 days. Litters are relatively small, usually 1-4 young (2-3 most common). Newborns develop rapidly and can leave nests within a month.

Activity patterns. Red Tree Voles are nocturnal and primarily arboreal.

Movements, Home range and Social organization. Red Tree Voles may have limited dispersalabilities, with young forests and recent clearcuts representing significant barriers to movement. Nests are located 2-65 m high in trees, often in lower one-third of crown of large old growth trees. Large branches can support large maternal nests or nurseries, but nests also are found in tree cavities or under moss covering large branches of old trees. Red Tree Voles often nest on top of abandoned bird nests or nests of other arboreal mammals. Occasionally other mammals (e.g. Western Gray Squirrels, Sciurus griseus) inhabit a single nest at the same time or sequentially.

Status and Conservation. Classified as Near Threatened on The IUCN Red List. Relatively low reproductive potential of Red Tree Voles and limited dispersal capabilities make them vulnerable to loss and fragmentation of preferred old growth forests by clearcut logging. Early seral stages or young forests can be dispersal barriers. Because Red Tree Voles have a relatively narrow environmental niche tied to large trees in old growth forests, industrial scale deforestation in Oregon and northern California (USA) is hypothesized as potentially problematic for their long-term persistence.

Bibliography. Bellinger et al. (2005), Corn & Bury (1988), Hafner et al. (1998), Hall (1981), Hayes (1996), Johnson & George (1991), Linzey & NatureServe (Scheuering & Hammerson) (2008), Manning & Maguire (1999), Meiselman & Doyle (1996), Musser & Carleton (2005), Thomas (1993), Verts & Carraway (1988).