Bechstein's bats maintain individual social links despite a complete reorganisation of their colony structure

Abstract

Several social mammals, including elephants and some primates, whales and bats, live in multi-level 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 7109 individual roosting records collected over four 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.