Roost Use of Operational Road Tunnels by Non-Cave Specialist Bats in a Subtropical Mountain Forest in Taiwan

It is known that the development of roadway systems can benefit bats, particularly cave- and crevice-roosting species, by providing novel roosting resources, e.g., abandoned tunnels and underpasses. However, the usage of operational road tunnels by bats, and its pros and cons are often overlooked. In the present study, we investigated bat diversity in 18 road tunnels in a subtropical forested mountain in Taiwan from 2018 to 2019. A total of 139 insectivorous bat sightings were recorded from 13 tunnels and 76.3% of the samples were identified to 12 species. Surprisingly, 75% of the species were previously regarded as non-cave specialists. Bat occurrences show spatial, temporal, and taxonomic aggregations as around 90% of the observations were contributed by four morpho-species from five tunnels in the summer and fall seasons. The among-site variations in species composition can be explained by tunnel morphology and presence of operational streetlight by the entrances. Since roadkill and grounded individuals, particularly juvenile Pipistrellus, were often found during surveys, these tunnels may act as ecological traps rather than suitable roosts to bats. Future confirmation of the roles of these tunnels to bats is necessary by measuring fitness through behavioral observations and long-term monitoring.