Published in Transactions of the Illinois State Academy of Science, Vol. 96 No. 2 (2003).


From May through July 2001, and June through August 2002 we surveyed 232 bridges in 9 southern Illinois counties for the presence of roosting bats. Fifteen bridges (6.5%) had bats roosting at the time they were surveyed. We encountered big brown bats (Eptesicus fuscus) most frequently. Eastern pipestrelles (Pipestrellus subflavus), little brown bats (Myotis lucifugus), and northern long-eared bats (M. septentrionalis) also were found roosting under bridges. The number of bats per bridge ranged from 1 to >100. Bats occurred in four of the five types of bridge designs surveyed. Of the 15 bridges with bats, 11 were rechecked at a later date to determine continuity of use. Seven of the 11 (63.6%) were being used by bats when rechecked. From this, we derived an estimated usage rate of 23.6 bridges (15/0.636) during the study, or about 10% of the 232 bridges surveyed. We could not determine relationships between bat presence and habitat features around bridges.