Phenacomys intermediuswestern heather vole

Geographic Range

Phenacomys intermedius (Heather vole) is found on the western mainland of the U.S. as far south as New Mexico. In Canada the vole is found across northern Canada from Labrador to the Yukon Territory. (Banfield 1974)(Fitzgerald 1994)


The Heather vole lives in stands of spruce, lodgepole pine, aspen, and grassy meadows in montane forest, subalpine, and alpine tundra (Fitzgerald 1994). The vole usually stays close to water. The Heather vole has been seen traveling 200 yards from its nest. The understory of their habitat may contain shrubs such as blueberry, dwarf birch, and soapberry. The Heather vole has been found as high as 12,100 feet elevation in Colorado. (Banfield 1974; Fitzgerald 1994; Armstrong 1972)

Physical Description

The Heather vole fur is long and soft. The color varies geographically. Generally, the dorsal colors are brown to grayish, while the ventral fur is gray. The feet are white to gray and the ears can have orange hairs. The tail is slightly longer than the hindfeet (31-34 mm) and has dark fur on top and is pale on the ventral side. The total length of the animal is between 130 and 140 mm. The species closely resembles the Meadow vole; skull characteristics are often needed to help tell the species apart. The skull characteristic used is that the cheek teeth have deep lingual angles in the Heather vole. (Banfield 1974; Fitzgerald 1994)

  • Range mass
    30 to 50 g
    1.06 to 1.76 oz
  • Average basal metabolic rate
    0.375 W


Heather voles have several estrus periods per year. Most of the breeding occurs between May and September. However, the voles located at higher elevations have a shorter season than the voles at lower elevations. Heather voles have a gestation period of 19 to 24 days. The litter size varies between 2 and 9, but variation is large because of the differences in litter sizes between adult and juvenile females. Adult females produce larger litters (average 5.9), while the juvenile females produce smaller litters (average 3.8) their first season. Three litters per year is believed to be the maximum produced. The voles are born blind and deaf. They finally wander out of the nest at about 3 weeks of age. Males don't reach sexual maturity until the next spring, while females reach sexual maturity 4-6 weeks after birth. (Banfield 1974; Fitzgerald 1994)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
  • Average gestation period
    22 days
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    37 days


Heather voles are active year round. The voles have different nesting areas depending on the time of the year. In the summer months, they live in burrow systems. These burrows are usually around 20 cm deep. The entrance is usually hidden by some sort of vegetation or leaf litter. The nest is made of grasses, lichen, and other types of vegetation.

The Heather vole does not hibernate. In the winter, the vole builds its nest on the surface of the ground under the snow. These nests are better insulated and have thicker walls made of lichen and twigs, and the nest is lined with grasses. Winter nests can be found in places of cover, such as under shrubs and logs. The vole in winter and summer months has an area it uses as a toilet. The toilet area is in a tunnel that extends from the nest.

The Heather vole usually leads a solitary life except during breeding season. In Canada, it was reported that in the winter family groups huddle together in communal nests (Banfield 1994). The female Heather vole takes care of the young and has a territory that she defends from other voles.

During the breeding season males fight among each other. The voles are active at dusk. Their predators include martens, weasels, owls, and hawks. (Banfield 1974; Fitzgerald 1994)

Communication and Perception

Food Habits

The Heather vole searches for green vegetation, bark of trees and shrubs, twigs, seeds, berries, and fungi. Their diet consists of leaves and fruits of willows, myrtle blueberry, snowberry, bog birch, kinnikinnnik (bearberry) in the summer months. In the winter, spring, and fall they tend to focus more on the bark and buds of willow, birch, and blueberry. The Heather vole stores food for use in the summer and winter. The food reserves are found close to the burrow entrances. (Banfield 1974; Fitzgerald 1994).

Economic Importance for Humans: Positive

There are no known ways that the Heather vole positively benefits humans at this time.

Economic Importance for Humans: Negative

The only adverse affect known at this time is the Heather vole has been known to carry the virus listeriosis (Banfield 1974).

Conservation Status

Other Comments

The population size of this species is not well known. Scientists have found the species difficult to trap and the mortality rate during livetrapping is high. (Fitzgerald 1994)


Brian Putz (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction that includes combining the genetic contribution of two individuals, a male and a female


uses touch to communicate


Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.


A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.


"U.S. Fish and Wildlife Service Homepage"" (On-line). Accessed December 12, 1999 at

Armstrong, D. 1972. Distribution of Mammals in Colorado. Lawrence, Kansas: University of Kansas Printing Service.

Banfield, A. 1974. The Mammals of Canada. Toronto, Canada: University of Toronto Press.

Fitzgerald, J., C. Meaney, D. Armstrong. 1994. Mammals of Colorado. Niwot, Colorado: University Press of Colorado.