Coordination and information transfer in bat colonies with fission-fusion behaviour

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To gain the maximum range of grouping benefits, group-living individuals typically need to coordinate their activities. Understanding the mechanisms, the causes, and the consequences of group coordination in animals, is thus a central focus of behavioural ecology. Our collaborative project aims for answering the questions how under natural conditions information transfer among group members leads to group coordination, using the communally breeding Bechstein’s bat, Myotis bechsteinii, as a model. Bechstein’s bat colonies show fission-fusion behaviour, i.e., splitting into subgroups and re-merging of subgroups, which switch their communal day roosts almost daily. Colony members coordinate their collective movements between roosts to ensure communal roosting, which provides them with grouping benefits such as social thermoregulation. Despite the importance of group coordination for the functioning of fission-fusion societies and the widespread occurrence of fission-fusion behaviour in bat colonies and other animal societies, only a few studies investigated information transfer and group coordination in wild fission-fusion societies. In this field study, we investigate how Bechstein's bat colonies coordinate their collective roost-switching. We use the recently established wireless biologging network BATS (Broadly Applicable Tracking System) to automatically collect data of nightly encounters of bats and their movements outside their roosts. In order to provide new insights in the coordination of collective roost-switching in bat colonies with high fission-fusion dynamics our study aims on identifying and quantifying the central behavioural elements that individuals use to find novel roosts and transfer information about communal roosts among each other (e.g., nightly approaches to roosts, leading-following behaviour, swarming behaviour). With the help of a field experiment we aim on assessing the flexibility of the coordination process, in particular with respect to the type of roost (familiar vs. novel roost) and the traits of the individuals involved (e.g., age, experience, kinship). Our project can build upon fully established field sites that are home to two Bechstein's bat colonies. These colonies have been monitored for up to 27 consecutive summers. All colony members are individually marked with PIT-tags and the bats’ demography and genetic relationships have been resolved. The significance of the project arises from the combination of a new cutting-edge technology (BATS- system) with an extraordinary long-term field data set on a bat species which has the potential to serve as a model for fission-fusion dynamics and group coordination behaviour. Our overarching goal is to improve the understanding of the functioning of animal societies with fission-fusion behaviour.