Roost Selection, Roost Availability and Gene Flow Among Culvert Roosts of a Trawling Bat in a Subtropical City

Many species of trawling bats roost in concrete culverts under roads. However, little is known about the selection of these artificial sites and how much gene flow occurs among culvert roosts.

We investigated culvert roost selection by Myotis macropus at two spatial scales and studied gene flow between culvert roosts in a large subtropical city in eastern Australia. We surveyed 365 concrete culverts, identified 23 roosts and collected wing tissue samples from 72 bats. Using generalized additive models, we found the distribution of M. macropus roosts in concrete culverts can be predicted at a landscape scale and culvert roosts were a limited resource with only 5.5% of culverts identified as potential roosts. We examined roost selection at the roost scale by comparing roost culverts to available culverts. Roost culverts differed significantly from available culverts and the primary difference was the availability of microhabitat. Culverts containing microhabitat were a limited resource in this urban landscape. We used single nucleotide polymorphisms to study gene flow among culvert roosts located in peri-urban and urban areas. Gene flow was moderate between peri-urban roosts and restricted between urban roosts. We found higher relatedness coefficients between individuals roosting in urban roosts compared to peri-urban roosts, indicating reduced gene flow between urban culvert roosts.

This study found that culvert roosts were limited at two spatial scales and that gene flow was restricted between urban culvert roosts. These findings suggest that disturbance to urban culvert roosts could be a significant impact to an urban population of M. macropus.