Little Mice in the Fields

Here's a little guy from Tussey Mountain, shot a couple of years ago:

Southern Red-backed Vole (Myodes gapperi), Tussey Mountain Hawkwatch,
Central Co., PA 3/27/2012

This is a Southern Red-backed Vole (Myodes gapperi), one of three species of Myodes and 26 species of vole to occur in North America. In any one area, there may be 5 or 6 species coexisting. When this happens, we expect to see some form of ecological separation between species, and the voles don't disappoint. For instance, in aspen parkland in Saskatchewan, this guy was found in aspen groves, whereas Meadow Voles (Microtus pennsylvanicus) were found in the surrounding grasslands. (1) Similarly, in Yellowstone NP, Mountain Voles (Microtus montanus) were found in open meadows, and Long-tailed Voles (Microtus longicaudus) in the ecotones between meadows and forests. (2)

In both cases, one of the two species was willing to use both habitats -- M. pennsylvanicus were found in aspen groves in Saskatchewan, (1) and M. longicaudus moved out into Yellowstone meadows when M. montanus were removed. (2) The opposite movements didn't occur, which indicates that one species was excluding the other from a preferred habitat, rather than each species living in the habitat it's best adapted to. Interestingly, in Saskatchewan, M. pennsylvanicus was found to use aspen parkland (M. gapperi's habitat) in the winter, whereas in Manitoba, the reverse was found to be true -- in the winter, M. gapperi moved into the open meadows preferred by M. pennsylvanicus. (3) These authors suggest that breeding voles are more aggressive and actively exclude the other species during the breeding season, but are less so during the winter. An alternative explanation may well be that populations are lower during the winter, and so competition is reduced.

These fine-scale habitat preferences can become very important when habitats change. European Field Voles (Microtus agrestis) were shown to drop significantly in abundance when habitat corridors (the unplowed margins of agricultural fields) became too narrow to support them. (4) If climate change, shifts in wildfire management, etc. were to affect the distribution of meadows and woodlands in an area, we would not only expect to see shifts in vole populations, but we would expect to see a similar threshold effect. This sort of non-linear reaction to habitat loss should be a distinct concern for wildlife managers everywhere.

Voles are fascinating little critters, even if we rarely get such a look. (This is the only species for which I have good photos of a wild, living individual.) With small home ranges and short reproductive times, they can provide a wonderful window into evolution and ecology.


(1) Morris, R. D. (1969). Competitive exclusion between Microtus and Clethrionomys in the aspen parkland of Saskatchewan. Journal of Mammalogy, 291-301.

(2) Anich, P. S., & Hadly, E. A. (2013). Asymmetrical Competition between Microtus montanus and Microtus longicaudus in the Greater Yellowstone Ecosystem. The American Midland Naturalist, 170(2), 274-286.

(3) Iverson, S. L., & Turner, B. N. (1972). Winter coexistence of Clethrionomys gapperi and Microtus pennsylvanicus in a grassland habitat. American Midland Naturalist, 440-445.

(4) Renwick, A. R., & Lambin, X. (2011). Abundance thresholds and the underlying ecological processes: Field voles Microtus agrestis in a fragmented landscape. Agriculture, Ecosystems & Environment, 144(1), 364-369.