Facing the rival: Directional singing behaviour in nightingales

摘要

Many animal vocalizations are directional, i.e. the sound energy is not emitted omnidirectionally but focused in one direction. Such signal property could be advantageous in order to direct the vocalization towards the addressee, provided its position is known to the sender. On the other hand, a directional signal could be disadvantageous when the position of addressees is not known. Thus, some animals may adjust their behaviour to either counteract or exploit the directionality of their vocalizations depending on the context of communication. We tested this hypotheses in territorial male nightingales (Luscinia megarhynchos) demonstrating the behavioural significance of vocal directionality for the first time. While interacting with the playback of a rival, the birds increased the strength of singing directionality by orientating themselves towards the playback loudspeaker. At the same time, subjects showed less lateral head movements per song during the playback procedure suggesting that nightingales mitigate the directional sound radiation pattern of their songs and emit them in a more omnidirectional way when the position of potential addressees is unclear. During interactions, however, when the position of a addressee is detected, the birds use the directionality of their songs to broadcast them in the direction of the addressee ensuring the most effective signal transmission.