Habitat
Prefers cool, mesic deciduous, coniferous, or mixed forests, especially areas with large amount of ground cover. Regarded as an ecological indicator of old-growth conditions in the Rocky Mountains. Also uses second-growth areas. Mossy logs and tree roots in coniferous forests are optimal. In the northern part of its range also found in muskegs, sedge marshes, shrubby habitats, and treed peatlands (Merritt, in Wilson and Ruff 1999). Often on rock outcrops in some areas (e.g., Virginia). Often associated with abandoned stone walls (fences) in the northeastern U.S. In Pennsylvania, abundance increased with forest fragmentation (Yahner 1992). Nests under logs, stumps and roots. Unlike MICROTUS, doesn't dig tunnels, but uses the burrows of moles and other small mammals.
Ecology
Disperses viable spores of mycorrhizal fungi and nitrogen-fixing bacteria (see Maser and Maser 1988).
Home range varies from 0.25 to 3.5 acres (Merritt and Merritt 1978). Experimentation by Gillis and Nams (1998) suggests that populations separated by an inter-patch distance of 60-70 m likely would be isolated from one another. Mature females are territorial. Populations noncyclic.
Reproduction
Breeds mid-January to late November; peak activity February-October. Gestation lasts 17-19 days. Litters size is 1-9 (average 5.6 in Alberta, 6.5 in Colorado). Litters/year: 1-4 for young, 1-6 for older females in Alberta; 2/year in Colorado (young of year breed).