Occurrence and Suspected Function of Prematernity Colonies of Eastern Pipistrelles, Perimyotis sub avus, in Indiana

Abstract

During summer, some pregnant female Eastern Pipistrelles form colonies in buildings but most typically roost in clusters of live or dead leaves in trees. We provide evidence that some that ultimately roost in leaf clusters form temporary colonies in or on buildings in early spring, prior to moving to the leaf clusters where they give birth. We call these prematernity colonies, and define them as those formed for a short time following hibernation and before the bats move to their maternity roosts. Prematernity colonies form from late April to early May and individuals relocate to leaf clusters from late May to early June. The bats showed strong fidelity to prematernity roosts, returning annually. Time of occupancy during any one year averaged 26 days. Nine bats were radio-tracked during the transition from building to tree roosts and were found to use several different trees. Bats showed interannual fidelity to building roosts. Buildings may help colonies re-form after individuals migrate from their hibernacula. Also, they could provide a warmer or more stable microclimate for pregnant females.