Effectiveness of pipe culverts in facilitating road crossings by clutter-adapted bats

• Pipe culverts could be useful as wildlife crossings for clutter-adapted bats. • Small pipe culverts (80 cm in diameter) are occasionally used by bats. • Bat activity increase with pipe culvert diameters. • Pipe culverts with water have higher bat activity. • Open-air foragers, such as the genus Pipistrellus did not use pipe culverts. Roads have several negative ecological effects on bats. Clutter-adapted bat species avoid roads as the open space increases the risk of predation. This results in the road acting as a barrier of movement, making otherwise suitable habitat inaccessible. Different approaches to mitigate the fragmentation and mortality caused by roads have been explored. Underpasses such as bridges or tunnels have proven to be used by clutter-adapted species to cross the road. A few studies have indicated that some species of bats could possibly use smaller structures such as pipe culverts. As pipe culverts are more cost-effective than bridges and tunnels, we set out to quantitively investigate what factors affect the usage of pipe culverts, aiming to produce recommendations for their implementation in the landscape. Clutter-adapted bats were surveyed with ultrasound detectors in 269 pipe culverts in Sweden. Each pipe culvert was surveyed for one night each and 73 pipe culverts with a high recorded activity were revisited and surveyed with mist nets. M. brandtii, M. daubentonii, M. mystacinus , M. nattereri, and P. auritus were found to be flying in the pipe culverts. Factors affecting the activity and usage of the pipe culverts were the width of the pipe culverts, presence of water in the pipe culvert and the presence of forest at the openings of the pipe culvert. The results give insight into how pipe culverts could be designed and implemented in landscape planning to mitigate the fragmentation caused by roads and decrease their negative effects on clutter-adapted bats.