Several social mammals, including elephants and some primates, whales and bats, live in multilevel societies that form temporary subgroups. Despite these fission-fusion dynamics, group members often maintain long-term bonds. However, it is unclear whether such individual links and the resulting stable social subunits continue to exist after a complete reorganisation of a society, e.g. following a population crash. Here, we employed a weighted network analysis on 7,109 individual roosting records collected over 4 years in a wild Bechstein's bat colony. We show that, in response to a strong population decline, the colony's two stable social subunits fused into a non-modular social network. Nevertheless, in the first year after the crash, long-term bonds were still detectable, suggesting that the bats remembered previous individual relationships. Our findings are important for understanding the flexibility of animal societies in the face of dramatic changes and for the conservation of social mammals with declining populations.

Most social animals depend on group decisions for coordination. Recent models suggest that the level of interindividual conflict strongly influences whether groups reach a consensus during decision making. However, few experimental studies have explored how wild animals make group decisions in situations with conflicting interests. Such experimental data are particularly lacking for animal societies with regular fission and fusion of subgroups. In this long-term study, we varied the level of conflict of interest among members of three wild Bechstein's bat (Myotis bechsteinii) colonies with high fission-fusion dynamics experimentally to explore whether the bats adapt their group decisions about communal roosts accordingly. In situations with low levels of conflict of interest, a minority of bats experiencing a roost as suitable was sufficient for a group consensus to use it communally. In contrast, if their interests diverged strongly, the bats no longer sought a compromise, but based their roosting decisions on individual preferences instead. Our results demonstrate that the rules applied to make group decisions can vary with the level of conflict among the individual interests of group members. Our findings are in agreement with predictions of the models and provide evidence for highly flexible group decisions within species.

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Leading-following behavior as a way of transferring information about the location of resources is widespread in dierent animal societies. However, it cannot always be observed directly. Here, we develop a general method to infer leading-following events from observational data if only the discrete appearance of individuals is recorded. Our method further allows to distinguish such events from local enhancement at the resource, such as swarming behavior in case of bats, which is another widespread way of transferring information among animals. To test our methodology, we analyze longitudinal data about the roosting behavior of Bechstein's bats from two dierent colonies and dierent years. The detection of leading-following events allows us, in a second step, to construct social networks in which nodes represent individual bats and directed and weighted links the leading-following events. We analyze the topology of these networks on the level of the colony, to see whether all individuals participate in leading-following behavior. Further, based on the leading-following network we measure the importance of individuals in this leading-following behavior by calculating dierent centrality measures. We nd that individuals can be consistently ranked regarding their inuence on others. Moreover, we identify a small set of individuals that play a central role in leading other bats to roosts. Our methodology can be used to understand the leading-following behavior and the individual impact of group members on the spread of information in animal groups in general.

In many social animals, group members exchange information about where to feed. Thereby, they may gain direct benefits, for example, if social hunting enhances individual foraging success. Alternatively, individuals may receive indirect fitness benefits by preferentially sharing information about suitable feeding sites with kin. Indeed, in some species, a positive correlation between the degree of relatedness among individuals and the overlap among their foraging areas was found. However, sharing foraging sites with kin can also have costs if it increases food competition, which is not compensated by direct benefits. The goal of this study was to investigate whether sharing of individual foraging areas in female Bechstein's bats is best explained by kin selection or by direct benefits through social foraging. To assess their individual foraging behaviour, we analysed radio‐tracking data of 22 members of one maternity colony, including nine mother–daughter pairs, seven pairs of less closely related individuals and six pairs of unrelated bats. We examined the bats' fidelity to specific foraging areas during several years and quantified the influence of kinship on the overlap among individual foraging areas. By measuring how close to each other the bats foraged, we assessed whether individuals with overlapping areas are likely to forage together. Our study confirms previous findings that Bechstein's bats show high fidelity to foraging areas across years. Moreover, we found that relatives share foraging areas significantly more often compared with unrelated colony members. Finally, our data reveal for the first time that most colony members that share foraging areas are unlikely to forage together. This suggests that female Bechstein's bats gain no direct benefits from sharing foraging areas with members of the same maternal lineage. Our findings also have implications for conservation as habitat loss within a colony's home range might expose entire matrilines to high risks.