In recent decades tree roosts of endangered Indiana bats (Myotis sodalis) have been more heavily studied than those of little brown bats (Myotis lucifugus), a much more common sympatric bat species. Motivated by precipitous declines in both species’ populations, we attempted to address this inconsistency by comparing the characteristics of these sibling species’ roosts. We used radio telemetry to find roosts of adult female bats of both species in two sites in southern Illinois and two sites in south-central Indiana. We then collected data on roost characteristics and bat movements. Little brown bats used more anthropogenic roosts and crevice/cavity roosts than Indiana bats, which used exfoliating bark roosts almost exclusively. Additionally, both species roosted in similar tree genera with similar DBHs (diameter at breast height) and roost heights. However, little brown bats roosted in shorter trees and in bigger clusters (based on emergence counts) than Indiana bats. Both species moved similar distances between roosts. However, little brown bats switched roosts slightly less often than Indiana bats. The potential preference for natural crevice/cavity roosts by little brown bats may have been a pre- adaptation that allowed the species to take advantage of the rapidly growing availability of crevice/cavity mimicking anthropogenic roosts during the spread of Europeans throughout North America.