Selection of Maternity Roosts by Big Brown Bats

Abstract

Exclusion is the recommended method for removing roosting bats from buildings, but is often difficult to accomplish. A simpler way to limit bat-human conflicts may be to modify new and existing buildings to discourage colonies from initially taking up residence. An understanding of the physical and micro-climatic characteristics of maternity roosts is a prerequisite when modifying buildings to discourage colonies. We investigated factors influencing maternity roost selection in big brown bats (Eptesicusfuscus) by comparing characteristics of bat-occupied buildings with bat-unoccupied buildings at 10 sites. Bat-occupied buildings were significantly older, more likely to have galvanized steel (tin) roofs, more accessible to bats, and taller than randomly selected unoccupied buildings. In paired surveys, occupied attics were significantly more accessible to bats than physically similar unoccupied attics and exhibited significantly higher temperatures and wider temperature gradients. Disturbance levels, light levels, and humidity did not differ between occupied and paired unoccupied attics. To discourage bats from initially establishing a maternity roost within a building, limit all access points. In buildings where this is difficult, attics can be made less suitable as roost sites by reducing attic temperatures during the summer months. Bat boxes intended to house displaced maternity colonies should be designed to provide high daily temperatures and wide temperature gradients.