Social influences on intergroup transfer by pine voles (Microtus pinetorum)

Selection to obtain mating opportunities is hypothesized to be a major factor in dispersal. Thus, if individuals move to another group or switch nests to maximize their reproductive opportunities, they should move to groups or sites where they minimize competition for resources or mates and where they can find potential mates. We examined movement of pine voles (Microtus pinetorum) in an orchard habitat. Males dispersed later than females, but the two sexes showed similar patterns of movement with respect to conspecifics. Males and females immigrated to territories that contained some opposite-sex conspecifics; they also immigrated to territories without same-sex conspecifics. The latter suggests that they may avoid competitors and move to territories where an opening exists. When female breeders were removed from a social group, a replacement female arrived and began to breed relatively rapidly. In control groups where breeding females were not removed, no replacement females appeared. These results suggest that pine voles, at least females, may monitor vacancies and immigrate if a vacancy appears.