By Dorothy Tucholska
Geographic Range
Originally thought to be restricted to the Canadian boreal coniferous forest, Microtus chrotorrhinus has also been found in the mixed forest of the transition zone in New York, West Virginia, Cape Breton Island (Nova Scotia) and Minnesota (Christian 1985). Currently the two subspecies of M. chrotorrhinus are found throughout the northern hardwood forests where appropriate microhabitat components are present (Kirkland et al. 1979) and the upper elevations of the northern Appalachians (Banfield 1974).
Habitat
Rock voles are specialized in their habitat selection and occupy cool, moist, rocky, northern hardwoods and mixed deciduous-coniferous forests dominated by Yellow Birch (Betula lutea), Sugar Maple (Acer saccharum), and American Beech (Fagus grandifolia). As their name indicates, rock voles live among mossy rocks and boulders in forests with moderately open canopies and a rich herbaceous under story. Rock voles are usually found in areas of small clearings or wind-downed trees where exposed boulders and crevices are visible (Christian et al. 1985). Water, either in the form of surface or subsurface streams, is another key habitat component (Kirkland et al. 1979).
The known predators of rock voles include hawks, owls, gulls, snakes, and other small carnivores (Forsyth 1985).
Terrestrial Biomes:
forest 
.
Physical Description
(1.06 to 1.69 oz; avg. 1.37 oz)
Microtus chrotorrhinus is one of the rarer North American small mammals. It is a medium sized vole, 140 to 185 mm long, weighing 30 to 48 grams (Kirkland et al. 1982). Rock voles are ventrally grayish brown back and dull to silvery gray with an orange face and rich yellow around the nose spreading backwards to include the ears. The winter coat is longer and glossier (Forsyth 1985). The ears are moderately large, tail is rather sparsely haired and of average length for a vole, 42 to 64 mm, also slightly paler below (Banfield 1974). Sexual dimorphism in this species is minute; males are usually slightly larger than females (Kirkland et al. 1982). A key identifying characteristic for this species is found in its dentition. The dental formula is 1/1, 0/0, 0/0, 3/3 = 16 teeth (Forsyth 1985). The third molar is characterized by five closed triangles (Banfield 1974).
Some key physical features:
endothermic ; bilateral symmetry .
Reproduction
M. chrotorrhinus breeds from early spring until late fall (Hamilton 1943). The gestation period is unknown but suspected to last 19 to 21 days (Kirkland 1982, Forsyth 1985). The litter size is 2 to 5 young with two or more litters per year, depending on female size (Kirkland 1982). The age of maturity for rock voles is probably 25 to 45 days; the lifespan is probably less than one year (Forsyth 1985).
Key reproductive features:
gonochoric/gonochoristic/dioecious (sexes separate); sexual .
Behavior
The literature provides only scarce comments on the behavior of M. chrotorrhinus in its natural environment (Kirkland et al. 1982). This species is primarily diurnal and most active in the morning (Goodwin 1929) but also reported to be active during the night (Timm 1977). Laboratory observations indicate that this species is docile and not aggressive when handled or exposed to other vole species. Females have been found to mate with M pensylvanicus males, but no viable offspring were produced. However, in nature, the ranges of these two species have not been found to overlap (Coventry 1937). Rock voles are not good nest builders, resulting in low survival of the young (Kirkland et al. 1982).
Key behaviors:
motile .
Food Habits
The primary food source of rock voles is Bunchberry (Cornus canadensis). The presence of this plant is thought to be indicative of the presence of M. chrotorrhius (Hamilton 1943). However, rock vole's diet also includes Clinton's Lily (Clintonia borealis), Canada mayflower (Maianthermum canadensis), False miterwort (Tiarella cordifolia), Wood Sorrel (Oxalis montana), mosses, and ferns (Banfield 1974, Christian et al. 1985). Rock voles cut herbaceous vegetation and pull the cuttings down into the subterranean galleries where they apparently spend much of their lives (Kirkland et al. 1979). Cut stems and leaves of forbs and other green plants can reveal the presence of M. chrotorrhinus.
Economic Importance for Humans: Negative
No information available
Economic Importance for Humans: Positive
No information available.
Conservation Status
IUCN Red List: [link]:
Lower Risk - Least Concern.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
Recent studies have found that rock voles occupy a much wider range than initially expected (Christian et al. 1985, Kirkland 1982). However, not much is known about their population densities (Christian et al. 1985). Some studies indicate population constancy (Jannett 1990) and therefore, M. chrotorrhinus is not considered threatened. Rock voles are found in small, localized populations occurring in fairly restricted, patchy habitat. Further research is needed to understand the implications of this pattern for conservation (Christian et al. 1985).
Other Comments
Microtus means "small ears" and chrotorrhinus means "color and nose", referring to their yellow noses (Banfield 1974).
.
Contributors
Dorothy Tucholska (author), University of Toronto.
