Summer Roosts of the Endangered Indiana Bat (Myotis sodalis) on the Northern Edge of Its Range

Abstract

-We discovered a reproductively active colony of the Indiana bat (Myotis sodalis) only 15 km S of the northern edge of the species' range in Michigan. Eight different roost trees were located, and all were green ash (Fraxinus pennsylvanica). This is the first report of Indiana bat maternity colonies using green ash. Unlike maternity colonies in more southern states, all roost trees in Michigan were exposed to direct sunlight throughout the day. Bats were still present as late as 10 September, well after the beginning of the swarming (mating) season at southern hibernacula. Population size at the main roost tree varied from 4-45. These bats roosted underneath the loose bark of dead trees, and we hypothesized that intertree movement was a response to the ephemeral nature of such roosting sites.