A population of rock voles, Microtus chrotorrhinus, which inhabited a large bed of boulders in northeastern Minnesota, was studied in August 1975. The voles did not occupy the entire boulder field, but rather appeared to be restricted to a narrow transition zone between the open rocks and mature forest. An interconnected system of runways was found in the crevices beneath and between the boulders. Litter size averaged 3.5, with some females producing at least three litters during the breeding season. Females born in late spring produced litters during their first summer. Notes on food habits, activity, parasites, cranial measurements, and associated species are included.
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):177–181.