Mihok, S., Schwartz, B. & Iverson, S.L. (1985) Ecology of red-backed voles (Clethrionomys gapperi) in a gradient of gamma radiation. pp. 257-271 in Stenseth, N.C. (Ed) Clethrionomys biology: Population dynamics, dispersal, reproduction and social structure. Annales Zoologica Fennici, Volume 22.

The demography of red-backed voles was monitored in boreal forest in southeastern Manitoba, Canada from 1967 to 1982. Catches on spring index lines and summer removal grids revealed only modest fluctuations in density with no evidence of a typical microtine population cycle. Beginning in 1973, four summer removal grids were exposed to an approximately exponentially decreasing field of gamma radiation from an artificial 137Cs source. Three grids located a few km from the irradiated area served as controls. Voles living in the irradiated area with very high dose rates were more likely to be immature and were smaller than voles living in areas exposed to lower dose rates. No other radiation-specific trends were detected. Major demographic differences occurred from year to year rather than between the irradiated and control area. Features characteristic of Clethrionomys species, such as inhibition of sexual maturity in young of the year at high density, were characteristic of all populations. Chronic exposure to radiation was insufficient to produce a depression in vole numbers. Radiation-induced death or sterility over an area of about 2-5 ha was presumably balanced by recruitment from surrounding areas exposed to lower levels of radiation. The inability of both the snap-trapping program and the radiation manipulation to affect demography suggests that Clethrionomys populations are insensitive to additional, random mortality. These results argue against the role of an established social structure in the regulation of population density.