Culvert design and position in the landscape predict the presence of trawling bat culvert roosts in an urban environment

Culvert design and position in the landscape predict the presence of trawling bat culvert roosts in an urban environment

Trawling bats occur in urban environments globally and are found roosting in artificial structures near water such as bridges and culverts. Culverts are suitable dark, thermally stable and often humid environments, however knowledge on roost selection and availability of these artificial structures within urban environments are limited. The large-footed myotis (Myotis macropus) is a specialist trawling bat found roosting in culverts under roads in urban environments in Australia. We used an experimental design stratified by landscape variables and culvert attributes to identify roosting preferences to predict culvert roost potential distribution and quantify the availability of suitable culvert roosts for a trawling bat in the subtropical city of Brisbane, Australia. We completed seasonal surveys of 308 concrete culverts across the city, modelled the distribution of M. macropus roosts and then predicted available culvert habitat. The distribution of M. macropus roosts in concrete culverts is related to waterway density, distance to nearest large waterbody, vegetation cover and channel width at the landscape scale, and to the height and design of the culvert at the culvert scale. Myotis macropus preferred culverts taller than 1.2 m in height, and while a preference for box culverts was detected, both box and pipe designs were occupied. Culverts available for selection as roosts by M. macropus are limited in the city of Brisbane urban landscape. Disturbance to or loss of culvert roosts can have significant conservation implications to colonies of trawling bats roosting in culverts due to the limited availability of concrete culverts that provide suitable roost sites.