22.

Western Heather Vole

Phenacomys intermedius

French: Phénacomys des bruyeres / German: Westliche Heidekraut-Wiihimaus / Spanish: Topillo de brezo occidental

Taxonomy. Phenacomys intermedius Merriam, 1889, “a basaltic plateau, about 20 miles [= 32 km] NNW of Kamloops,” 5500 feet (= 1676 m), British Columbia, Canada.

Taxonomic: status of P; intermedius: and P. ungava remains unsettled and should be further scrutinized. Phenacomys ungava was considered a subspecies of P. intermedius by many authorities. Five subspecies recognized.

Subspecies and Distribution.

P.i.intermediusMerriam,1889—fromW BritishColumbia,Canada,SEtoNNewMexico,USA.

Pu.celsusA.B.Howell,1923—SierraNevadaofECCaliforniaandextremeWNevada,USA.

P.i.laingiR.M.Anderson,1942—SWBritishColumbia,Canada.

P1.levisA.B.Howell,1923—fromEBritishColumbiaandWCAlberta,Canada,SEtoNWMontana,USA.

P.i. oramontis Rhoads, 1895 — from S British Columbia, Canada, S to C Oregon, USA.

Descriptive notes. Head-body 104-112 mm, tail 26-41 mm, ear 11-17 mm, hindfoot 16-18 mm; weight 40 g (average). The Western Heather Vole is small and short-tailed, with dorsal pelage agouti-gray to brownish and venter whitish or grayish. Unlike most other arvicolines, molars of the two species of Phenacomys are rooted in adults. Diploid number is 2n = 56.

Habitat. Heather-like vegetation in upland conifer forests, upland mixed forests, and above timberline in stunted, deformed vegetation, in subalpine landscapes (“krumholtz”) and moist alpine meadows. Common habitats of the Western Heather Vole are willow ( Salix sp.) thickets and balsam poplar ( Populus balsamifera), both Salicaceae; dwarf birch ( Betula glandulosa, Betulaceae); grassy meadows ( Festuca altaica, Poaceae); open spruce ( Picea glauca, Pinaceae) and open aspen ( Populus tremuloides).

Food and Feeding. The Western Heather Vole eats twigs, bark, roots, leaves, fruit, seeds, and lichens. Bearberry ( Arctostaphylos uva-ursi, Ericaceae) is especially important, along with soapberry ( Shepherdia canadensis, Fleagnaceae) and mountain cranberry ( Vaccinium vitis-idaea, Fricaceae). Near entrances to burrows, Western Heather Voles cache food year-round. Common plants found in caches are willow, blueberry ( Vaccinium sp.), soapberry ( Shepherdia sp.), bearberry ( Arctostaphylos sp.), crowberry ( Empetrum sp., Ericaceae), and fireweed ( Epilobium sp., Onagraceae).

Breeding. Breeding of Western Heather Voles occurs in May-August, with shorter seasons at higher elevations and latitudes. Gestation lasts 19-24 days, and up to 3 litters/year have been recorded. Meanlitter size is higher for over-wintered females (4-4 young) than average (3-6 young) for first-year breeders. Latitude also plays a role in litter size, with larger litters reported from southern parts of the distribution. Females are sexually mature and able to breed at 4-6 weeks old. Newborns are altricial at birth (i.e. pink, wrinkled, hairless, and blind) but develop rapidly. In alpine areas of the Rocky Mountains of Colorado, USA, a cohort young Western Heather Voles gained an average of 0-82 g/ day during theirfirst 21 days.

Activity patterns. Western Heather Voles are most active beginning in the evening and through the night. Bad weather can increase foraging activity.

Movements, Home range and Social organization. Life span of the Western Heather Vole is up to four years based on studies of cranial morphology and toothwear. It uses different nests in winter and summer. Winter nests are c.15 cm in diameter and often located below snow and above ground at bases of bushes, stumps, or rocks. Summer nests are smaller and found under boards, moundsleft by rotten stumps, peat, or rock and in stumps, logs, or roots of small trees. It uses latrine sites where feces become concentrated. Although Western Heather Voles are broadly distributed, they are rarely captured with traditional snap traps and live traps. In one study, they were found in 5% ofall Marten (Martes americana) scats analyzed, suggesting their densities may be higher than revealed by traditional survey trapping efforts.

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

Bibliography. Banfield (1974), Bradley, Ammerman et al. (2014), Chavez & Kenagy (2010), Foster (1961), Hall (1981), Halfpenny & Ingraham (1983), MacDonald et al. (2004), Musser & Carleton (2005), Wilson & Ruff (1999).