The Social Organization and Behavior of the Brown Long-Eared Bat Plecotus auritus

Abstract

The complexity of the social behavior and social organization of bats arises from the philopatry of females, stable group composition, and hence cooperation with colony members, which in turn influences the mating system of particular species. Understanding the relationship between social organization and mating system is crucial for understanding the behavior of animals. I have studied the social organization and social and mating behavior of a temperate zone species of bat, the brown long-eared bat Plecotus auritus, for over 13 years in SW Poland using genetic and behavioral methods. The obtained results enable me to complete and explain the pattern of social organization and mating behavior in this species. P. auritus lives in small, stable, and isolated maternity colonies (usually up to 40–50 individuals, including adult resident males) and swarms in underground hibernacula during autumn and spring. Members of the colony use low frequency contact calls when they emerge and return to the roosts and during dawn swarming. The peak of this vocal activity falls between July and September and in the morning. Around 28–38 % of colony members emerge or return in pairs, or sometimes in groups of 3–4 individuals emitting social calls. Before leaving the roost, and after arrival, 10–16 % of bat activity involves tandem flights. This behavior may play a role in the maintenance of social bonds between mates in the roost. Some members of the maternity colonies and solitary males frequently travel to the underground hibernacula from day roosts as far away as 31.5 km every autumn and spring to swarm with bats from other colonies. Swarming populations are large and may gather up to several hundred individuals from several colonies. Swarming bats usually stay in swarming sites for several hours before returning to a day roost, vocalizing and intensively flying, sometimes in groups of 2 or more individuals. Colonies and groups of swarming bats show high gene diversities and low inbreeding coefficients, and they are not genetically isolated by distance, which suggests high gene flow between sites and the mating function of autumn and spring swarming. Therefore, inbreeding is avoided in these philopatric and spatially isolated colonies by swarming behavior and mating in hibernacula in the autumn and spring. This work indicates that P. auritus appears to be unusual among European temperate zone bat species in its maternity colony composition and stability (resident females accompanied by resident males), biphasic swarming season (in autumn and spring), and distinctive vocal activity in swarming sites and maternity colonies. The social structure and behavior of P. auritus is complex and suggests the existence of close and stable society-like groups in this species.