Roosting Ecology of the Northern Bat (Myotis septentrionalis) and Comparisons with the Endangered Indiana Bat (Myotis sodalis)

During 1993 and 1994, we radiotracked 11 adult female and juvenile northern bats ( Myotis septentrionalis ) to 32 roost trees: 18 silver maples ( Acer saccharinum ), 1 red maple (A. rubrum ), and 13 green ashes ( Fraxinus pennsylvanica ). Fifty-three percent of the trees were living; 52% of the roosts were in crevices or hollows, and the rest were under exfoliating bark. Northern bats did not use American elms ( Ulmus americana ) in proportion to their abundance, but in general, characteristics of roost trees were similar to a random sample of apparently suitable trees. Northern bats changed roosts every 2 days, and distance between roosts varied from 6 to 2,000 m. As many as 60 adults were found in a single tree, making this the largest summer aggregation ever reported for the species. Compared with Indiana bats ( M. sodalis ) separately studied at the same site, northern bats moved greater distances between roosts and roosted more often in maples, cavities, living trees, and areas with high canopy cover.