Download Microtus chrotorrhinus

Microtus chrotorrhinus
Rock Vole, Yellownose Vole
by Eric C. Tauchman
Description
Microtus chrotorrhinus is usually a grayish brown color dorsally, frequently with
black-tipped hairs. The distinguishing face is yellowish to orange rust that is most
vibrant on the snout and fades toward the ears. The degree and intensity of this
coloration varies due to age and locality. The rock vole is an average sized vole
measuring 140 to 185 mm from snout to tail tip, with the tail comprising 42 to 64 mm of
its length. Males of the species tend to be slightly larger (Kirkland and Jannett, 1982). It
has a dental formula of 1/1, 0/0, 0/0, 3/3 totaling sixteen teeth (Kurta, 1995). The molars
are rootless, growing continually and the occlusal surfaces are helpful in distinguishing
the rock vole from other voles (Kirkland and Jannett, 1982).
Distribution
M. chrotorrhinus ranges from northeastern Minnesota and southwestern Ontario,
east to Labrador and the Maritime Provinces in Canada. In eastern North America, it is
found as far north as Cape Breton Island and south through the Appalachian Mountains to
the Virginias and North Carolina (Kirkland and Jannett, 1982; Pagels, 1990). Rock voles
are relatively scarce and tend to live in small, isolated patches. While they were
traditionally thought to inhabit boreal habitats at higher elevations (above 600m), they
have since been trapped in openings in moist forest, in Transition Zone habitats,
hardwood forests, and in dense grass or meadow habitats (Christian and Daniels, 1985;
Timm et al. 1977). This indicates that rock voles are geographically more widespread
and have a greater ecological range than previously known (Kirkland and Knipe, 1979).
Though acceptable habitats do exist in Wisconsin, especially in the North and West areas
of the state, throughout its range the rock vole does not inhabit seemingly appropriate
environments (Hamilton and Whitaker, 1979) and this appears to be the case in
Wisconsin.
Ontogeny and Reproduction
M. chrotorrhinus breeds early in the spring until mid to late fall with a gestation
period lasting 19 to 21 days (Kirkland and Jannett, 1982; Jannett, 1987). Females
produce three or more litters during the season and those born in spring will produce
litters their first summer. An average litter size is 3.5 young (Timm et al. 1977) and
range from 2 to 5 with larger, older females producing the most young (Kirkland and
Jannett, 1982). Females then quickly abandon juveniles after weaning (Jannett. 1987).
Ecology and Behavior
As the common name implies, rock voles inhabit areas where rocks or boulders
are prominent environmental elements, and they seem especially preferential to rock
crevices. Mosses, ferns and forbs also tend to be included in their habitat (Kirkland and
Knipe, 1979; Pagels, 1990). Black Spruce (Picea mariana), Paper Birch (Betula
papyrifa), White Cedar (Thuja occidentalis), and Balsam Fir (Abies balsamea) are often
the dominant trees though they are found most often in areas of open canopy. Downed
trees that expose underlying boulders and crevices are sites that frequently shelter rock
voles (Christian and Daniels, 1985). Additional flora dominating the rock vole’s habitat
includes Bunchberry (Cornus Canadensis), Blueberry (Vaccinium angustifolium), Aster
(Aster macrophyllus), and Clinton’s Lily (Clintonia borealis). Furthermore, water, either
standing or flowing; surface or subsurface is an important habitat component (Timm et
al. 1977, Kirkland and Knipe, 1979).
Food habits of Microtus chrotorrhinus in the northeastern portion of their range
were studied by the analysis of the stomach contents of 47 specimens. Whitaker and
Martin (1977) found Bunchberry to be an elemental part of the rock vole’s diet. They
found it accounted for 47 percent of the stomach volume, and their laboratory study
confirmed the species partiality toward this plant. They also found it to eat a variety of
green vegetation, mosses, and lepidopterous larvae. Forbs and leaves from ericaceous
plant species have also been noted as an important dietary component (Donato, 1998).
Additionally, captive voles in Minnesota ate Blueberry, Raspberry (Rubus strigosus), and
many types of insects (Timm et al. 1977).
Little is known about the behavior of M. chrotorrhinus (Kirkland and Jannett,
1982). Systems of subterranean runways are found in conjunction with the rock voles
habitat and many are captured in these or similar subsurface places (Kirkland and Knipe,
1979, Timm et al. 1977). This is a good indication that the rock vole spends the majority
of its time below ground (Kirkland and Jannett, 1982). From trapping data, it seems to be
most active in the day and night, being less so during the afternoon hours (Timm et al.
1977). This behavior likely arises from a desire to avoid predation thought they do fall
prey to Bobcats (Lynx rufus), Weasels (Mustela sp.), Short-tailed Shrews (Blarina
Brevicauda), snakes, and some raptors (Kirkland and Jannett, 1982, Donato, 1998).
They also have little social structure (Jannett, 1987), though the females will sometimes
exclude males from the nest while they are nursing (Kirkland and Jannett, 1982).
An important aspect of Microtus chrotorrhinus is that its populations are
discontinuous, isolated, (Christian and Daniels, 1985; Kirkland and Jannett, 1982) and
small to the point where trapping capture nearly all individuals of a colony (Hamilton and
Whitaker, 1979). This geographic isolation reduces gene flow likely accounting for
variation amongst the three subspecies—Southern populations of rock voles have slightly
darker pelage and somewhat more robust skulls than their northern counterparts
(Kirkland and Jannett, 1982). However, the frequency of inbreeding in M. chrotorrhinus
is consistent with other rodents, and the level of genetic heterozygosity the voles display
is actually above average for rodent populations (Kilpatrick and Crowell, 1985). This
would seem indicative of at least some interpopulation migratory action by the rock
voles.
Remarks:
There are three subspecies of Microtus chrotorrhinus: M.c. chrotorrhinus being
the most widespread inhabiting Minnesota, Northern Appalachia, and most Canadian
species, M.c. carolinensis occupying Southern Appalachia, and M.c. ravus, the smallest,
is restricted to Labrador (Kirkland and Jannett, 1982).
Microtus chrotorrhinus stems from the Greek chrotorrhinus meaning, “colored
nose” (Donato, 1998).
References:
Christian, D. P., and J. M. Daniels. 1985. Distributional Records of Rock Voles,
Microtus chrotorrhinus, in Northeastern Minnesota. Canadian Field-Naturalist,
99(3): 356-359.
Donato, S. 1998. Habitat use and Dietary Habits of Yellownose voles (Microtus
chrotorrhinus), meadow voles (Microtus pennsylvanicus), and red-backed voles
(Clethrionomys gapperi) in Logged and Mature Black Spruce Stands in the
Claybelt of Northeastern Ontario. MSc. Laurentian University.
Hamilton, J. H., Jr. and J. O. Whitaker, Jr. Mammals of the Eastern United States. 1979.
Comstock Publishing Associates. Cornell Univ. Press, Ithaca and New York.
Jannett, F. J., Jr. 1987. Habitat Breadth and Population Stability and Structure of the
Rock Vole, Microtus chrotorrhinus, in Northeastern Minnesota. American
Zoologist. 27(4): 45A.
Kilpatrick, W. C., and K. L. Crowell. 1985. Genetic Variation of the Rock Vole,
Microtus chrotorrhinus. Journal of Mammalogy, 66(1): 94-101.
Kirkland, G. L., Jr. and F. J. Jannett, Jr. 1982. Microtus chrotorrhinus. Mammalian
Species, 180: 1-5.
Kirkland, G. L., Jr. and C. M. Knipe. 1979. The Rock Vole (Microtus chrotorrhinus) as a
Transition Zone Species. Canadian Field-Naturalist, 91(2): 177-181.
Kurta, Allen. 1995. Mammals of the Great Lakes Region. University of Michigan Press,
Ann Arbor, Michigan.
Pagels, J. F. 1990. First Record of the Rock Vole, Microtus chrotorrhinus, (Miller)
(Rodentia: Cricetitae), in Virginia. Brimleyana, No. 16: 1-3.
Timm, R. M., L. R. Heaney, and D. D. Baird. 1977. Natural History of Rock Voles
(Microtus chrotorrhinus) in Minnesota. Canadian Field-Naturalist, 91(2): 177181.
Whitaker, J. O., Jr. and R. L. Martin. 1977. Food Habits of Microtus chrotorrhinus from
New Hampshire, New York, Labrador, and Quebec. Journal of Mammalogy,
58(1): 99-100.
Reference written by Eric C. Tauchman, Biol 378: Edited by Chris Yahnke.
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