Social Organization of a Free-Ranging Population of Pine Voles, Microtus pinetorum

Free-ranging pine voles (Microtus pinetorum) were radiotracked on four separate occasions between August 1980 and July 1981 in an apple orchard in Ulster County, New York USA. Positions were recorded hourly for a total of five 24-h periods during each of the four telemetry sessions. A total of 76 voles were radiotracked (x̄ = 19/session) over the course of the study. Pine voles existed in non-overlapping extended family units with a mean of 4.2 (range 2-9) individuals per unit (Figs. 1 and 3). All family members utilized one or two nest sites within the group's exclusive territory (Fig. 2), regardless of sex or reproductive condition. Home range areas ($\text{range}=6\ {\rm m}^{2}-102\ {\rm m}^{2}$) estimated for males and females were not significantly different. Based on telemetry revealed associations between reproductively active individuals, the pine vole mating system appears to be monogamous. However, cooperative polyandry in multi-male units is a distinct possibility.