Should i stay or should i go? Fission-fusion dynamics in bats

Abstract

Animal species with fission-fusion dynamics are characterized by variable group size and composition, as individuals move freely among a social network. Patterns consistent with fission-fusion dynamics appear to be widespread in bats and interest in these patterns has advanced our general understanding of proximate and ultimate explanations for fission-fusion dynamics. Here, we explore the following questions: (1) Why do bats switch roosts? (2) Why do not group members move together? (3) Do bats form social bonds despite frequent roost switching? (4) If group members do form social relationships, what shapes these relationships? (5) How are social relationships maintained in these dynamic systems? (6) What does our understanding about fission-fusion in bats tell us about the evolution of fission-fusion dynamics in general? In our review, we show that bats switch roosts for a combination of reasons, including to reduce predation, parasites, and disease, and to minimize commutes. The strongest evidence, however, suggests bats switch roosts to seek more suitable roosts when roost quality changes. However, the degree to which each of these factors influences roost switching varies between individuals, across species, and depends on preferred roost type and roost availability. Group members may not move together because they experience different perceived costs and benefits of remaining in a group. Bats apparently use a combination of spatial and sensory information to relocate group members and maintain social bonds. Bat populations with fission-fusion dynamics likely benefit from social thermoregulation, and share information about roosts and foraging sites. Although our understanding of these dynamics has improved in recent years, many questions remain. For instance, a better understanding of the proximate factors driving fission-fusion dynamics is required. Establishing the levels at which bats sharing the same roost interact, together with network analyses, would also advance our understanding of relationships within these dynamic groups. Together, answers to these and other questions will help us to better manage bat populations and their habitat.