Functions of Bat Social Calls: The Influence of Local Abundance, Interspecific Interactions and Season on the Production of Pipistrelle (Pipistrellus pipistrellus) Type D Social Calls

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We studied the social call rate of the common pipistrelle (Pipistrellus pipistrellus) in natural habitats in relation to the presence or absence of conspecifics and of other bat species by acoustical and behavioural monitoring and analyses. The relative frequency of type D social calls increased, when more than one individual of P. pipistrellus was present, compared to one individual. The data confirm the assumption that one function of social calls is repelling conspecifics (food patch defence hypothesis). In the presence of other species of the genus Pipistrellus or of other genera, the mean social call rate did not significantly increase, except when P. pygmaeus was present. Hence, social call production as a food patch defence typically is not significantly influenced by interspecific interactions. This directs to niche separation concerning the foraging mode of different species. The closely related species P. pipistrellus and P. pygmaeus may compete for resources and communicate by type D social calls. Pipistrelles are known to use a series of type D social calls during songflights. For instance, males use this calling behaviour to attract females and repel competing males. During the mating season P. pipistrellus produced social calls more frequently when other pipistrelle species were absent. This shows that interspecific recognition may influence the mating behaviour of P. pipistrellus. Competing for non-food resources like mating roosts may cause bats to keep calm in the presence of other species.