(Uploaded by Plazi for the Bat Literature Project) We compared roost site characteristics of the Indiana bat (Myotis sodalis) and northern bat (M. septentrionalis), which form maternity colonies in cavities and beneath bark of dead (snags) and living trees in eastern North American forests. We used published data (n 5 28 sources; n 5 1145 roost trees) from studies completed where the distributions of the two species overlap and evaluated a suite of habitat features that might affect roost selection and interspecific competition between these two congeners. We found no differences between these species in average height of roost aboveground, density of snags in the vicinity of roosts, selection of live trees versus snags or relative elevation. Populations of northern bats were more likely to choose roosts in crevices or cavities (88.9%) than Indiana bats (30.0%; P , 0.1), and roosted in trees that averaged smaller in diameter (30.0 6 5.4 cm) than trees selected by Indiana bats (41.4 6 2.4 cm; P , 0.1). Northern bats demonstrated greater variability than Indiana bats in height of roosts aboveground and in stem diameter of roost trees. Existing data indicate northern bats exhibit greater plasticity in choice of summer roosts than Indiana bats, explaining, in part, why northern bats are more widely distributed and more common in forests of eastern North America than are Indiana bats.