A Population Study of the Vole, Microtus pennsylvanicus

Owing to the amount of time and effort required to live-trap small mammals, comparatively little is known concerning the population phenomena of even the more common species. One such species is the meadow vole, Microtus pennsylvanicus. Although several studies have been made of this rodent (Gunderson, 1950; Blair, 1948; Hamilton, 1940; Linduska, 1950), for the most part the investigators utilized snap-trapping data or based their results on live-trapping studies in which the intervals between trapping periods were longer than desirable, considering the rate of change of the various population factors. The short life span, as well as the rapid growth and development of M. pennsylvanicus, necessitates that samples of the population under study be taken at least at monthly intervals. Studies made at lesser intervals (or continuously) would permit following the population changes even more closely. Since trapping disturbs the population to a certain extent (death of animals in the traps and restriction of movements), intervals of less than one month may result in disturbances sufficient to offset the advantages gained by the closer inspection of the population. Consequently, an interval of approximately one month between trapping periods seems to be a suitable compromise. The data presented in this paper were obtained during the course of a study of the ecology of M. pennsylvanicus in southern Michigan. Other phases of the study, being published separately, include an analysis of the factors influencing the local distribution of the species (Getz, in Press) and its home range, territoriality, and movement (in Preparation).