The ecology of vocal signaling : male spacing and communication distance of different song traits in nightingales

The ecology of a species and its communication system require mutual adaptations. Specifically, information transfer between individuals needs to be adapted to the social and ecological requirements and constraints. As a consequence, constraints on signal transmission are likely to play a role in the evolution of spatiotemporal behavior and settlement and vice versa. In long-distance signaling, such as in bird song, adaptations can be reflected in specific signal structures that transmit to a socially relevant distance without degradation masking the coded information. Here, we studied sound transmission properties of 2 different song components in male nightingale (Luscinia megarhynchos) territorial song, i.e., transmission of whistle songs and songs with rapid broadband trills. We also determined spacing of nocturnal song posts using a global positioning system. The results revealed highly significant differences in transmission of the 2 functionally different song traits, with information in whistles traveling well beyond the typical spacing between neighboring individuals. Information coded in trills bandwidth did not even travel the average distance toward the nearest neighbor, showing that information coded in trill bandwidth is not available for receivers at typical spacing distances. The results emphasize that for a better understanding of evolutionary processes in communication, ecological components such as spatial distance as well as signal structure and signal degradation have to be taken into account.