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.