Communal nesting between reproductively active females in a spring population of Microtus pennsylvanicus

Weekly livetrapping and radiotelemetry of a spring population of Microtus pennsylvanicus revealed communal nesting by reproductively active females. In several instances the communal nesting involved at least one female who was nursing young in the nest. Two of these instances involved what appeared to be more than one litter. Continuous monitoring over a 42-h period of one double litter confirmed the presence of two females who also differed in their nursing rhythms. Occurrences of conesting decreased through the spring, possibly because of increasing temperatures or the disappearance of nest partners.