Bats under an Indiana Bridge

Abstract

A survey of over 200 bridges and culverts in southwest Indiana was completed in 2004 and
2005. Only a single bridge showed roosting bats, including federally endangered Indiana bats (Myotis sodalis) and gray bats (Myotis grisescens). Other species present included little brown bats (Myotis lucifugus), big brown bats (Eptesicus fuscus), and eastern pipistelles (Perimyotis subflavus) or now called tri-colored bats. Surveys of this bridge occurred 2006 to 2011. The little brown bat was the most common (6,887) followed by Indiana (878), big brown (774), eastern pipistrelle (29), and gray bat (2). There were more male than female Indiana and little brown bats, especially in the late summer and early fall. The bridge serves as a mating site, day/night roost, and migratory stop-over for little brown bats and Indiana bats. Big brown bats were found throughout the year, while eastern pipistrelles were occasional in winter to early spring. Banding showed many bats have a high fidelity to this bridge, and wing membrane scores did not indicate white-nose syndrome (WNS). Data loggers were placed under the bridge for temperature readings from July 2008 to March 2009 and showed Myotis avoiding them (but Eptesicus did not) due to ultrasonic noise at about 30 kHz. The bridge acted as a thermal sink at night and throughout most of the day, especially during warmer months. The bridge was warmer and had more constant temperatures than outside temperatures from July to February.