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).
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).
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).
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).
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).
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.
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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).
Microtus means "small ears" and chrotorrhinus means "color and nose", referring to their yellow noses (Banfield 1974).
Dorothy Tucholska (author), University of Toronto.
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.
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.
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
Banfield, A. 1974. The Mammals of Canada. Toronto, Canada.: University of Toronto Press.
Christian, D., J. Daniels. 1985. Distributional Records of Rock Voles, *Microtus chrotorrhinus*, in Northeastern Minnesota.. Canadian Field Naturalist, 99: 356-359.
Coventry, A. 1937. Notes of the breeding of some cricetidae in Ontario. Journal of Mammalogy, 18: 489-496.
Forsyth, A. 1985. Mammals of the Canadian Wild. Ontario: Canden House Publishing Ltd..
Hamilton, W. J., Jr, 1943. The mammals of eastern United States.. Ithaca, New York.: Comstock Publ. Co..
Jannett, F. 1990. Population constancy of the rock vole, *Microtus chrotorrhinus*, in northeastern Minnesota. From Tamarin, R.H., Ostfeld, R.S., Pugh, S.R. amp; Bujalska, G. [Eds]. Social systems and population cycles in voles. Boston & Berlin: Birkhauser Verlag, Basel,.
Kirkland Jr., Gordon L., , Jannett Jr., Frederick J.. 1982. Mammalian Species - Microtus chrotorrhinus. The American Society of Mammalogists, No. 180: 1-5.
Kirkland, J., C. Knipe. 1979. The Rock Vole (*Microtus chrotorrhinus*) as a Transition Zone Species.. Canadian Field Naturalist, 1979: 319-321.
Timm, R., L. Heaney, D. Baird. 1977. Natural history of rock vole (*Microtus chrotorrhinus*) in Minnesota.. Canadian Field Naturalist, 91: 177-181.