Little is known about the social behaviour of roosting insectivorous bats in Australia. Interactions between individuals and movements between multiple roosts at a building maternity site of the chocolate wattled bat (Chalinolobus morio) were examined using video observation and Passive Integrated Transponder (PIT) tagging, respectively. Bats of both sexes were seen to allogroom, which involved pairs of individuals simultaneously grooming each other around the face. This is the first occurrence of allogrooming reported between male vespertilionids, globally. In total, 366 bats were PIT tagged and analysis of movements revealed that bats exhibited a fission–fusion pattern of roost usage with sufficient switching among nearby roosts, such that all individuals were potentially able to associate and interact over a period of 150–200 days. Rates of roost fidelity varied markedly from 1 to 7.2 days of continuous occupancy of roosts, with females exhibiting slightly higher overall levels of fidelity over the nine-month monitoring period. The information gained from this study, when combined with results from other research, provides a sufficient basis for the description of the apparent breeding system for this species, where both males and females at the summer maternity roost are natally philopatric and mating takes place over winter in an expanded gene pool, comprising individuals that have dispersed from multiple summer maternity roosts.