Roost Fidelity and Fission–Fusion Dynamics of White-striped Free-tailed Bats (Tadarida australis)

Abstract

The white-striped free-tailed bat (Tadarida australis) is a common species of insectivorous bat found in mainland Australia. Despite its abundance, very little is known about its roosting ecology. I used radiotelemetry collected during 3 seasons to examine roost fidelity and roosting associations of a summer roosting group. Bats were trapped at a large communal roost in subtropical urban Brisbane, Australia. A total of 132 radiotracking days and nights provided 509 bat-days of data, with each bat being tracked for 26.9 days 6 28.6 SD. Seventeen new roost trees were found, scattered throughout an area of .200 km 2 . Roost cavities were located inside eucalypt trees .83 cm diameter at breast height. Tagged T. australis switched roosts every 10.6 6 7.9 days on average and spent most of their time in day-roosts with smaller roosting groups despite being 1st caught at the communal roost. I quantified associations between pairs of tagged bats using a pairwise sharing index. The consistent negative values of the pairwise sharing index I calculated indicated that members associated with roost-mates less often than predicted by chance. However, bats typically associated at night at the communal roost, even when they did not occupy it during the day. For every day-visit recorded per bat at the communal roost, each bat visited the same roost twice at night on average. This suggests that nocturnal movements of individuals should be included in assessments of associations between individuals. I postulate that this species employs a fission‐fusion pattern based on individual movements to and from 1 communal site. I also argue that the roost network of 1 communal roost and many satellite roosts may be regarded as a single interconnected unit.