Abstract:
Aggressive behaviours have an important impact on the social organization of animals and on the social status of individuals, especially in gregarious species. Agonistic interactions between territory holders are essential to set and reinforce territorial borders. Additionally, agonistic displays are used to demonstrate ownership of a territorial site and may indicate social status of the signaller. Between neighbouring territory owners, dynamic borders require frequent interactions. In daily repeated aggressive encounters, ritualization can help to avoid the need for serious fights and their costly consequences. In the bat Carollia perspicillata, a gregarious frugivore with resource defence polygyny, males defend territories at valuable roosting sites for females. Working with a captive bat colony of about 400 individuals, housed under seminatural conditions in a tropical zoo, we found that males defended territories aggressively by the use of a succession of displays forming a ritualized structure. Simultaneously, males used three different vocalization types during aggressive displays, namely down-sweeps, warbles and aggressive trills. A statistical analysis of 58 aggressive trills from five adult males showed that they contained sufficient variation to encode an individual signature. Using a habituation dishabituation paradigm playback experiment, we found that males could discriminate between vocalizing males based on aggressive calls alone. Such discrimination is probably useful for distinguishing between neighbouring territory owners and more unfamiliar intruders, and thus allows for an economical response.
