The Song of the Willow Warbler Phylloscopus trochilus with Special Reference to Singing Behaviour in Agonistic Situations

Abstract

During territorial combats the songs of the Willow Warbler male change in a number of parameters from singing heard in undisturbed situations. The song become shorter, muter and somewhat lower pitched. There is also heard a special type of song (the A-song) which is characterized by the introduction of a special syllable type in the beginning of each song. Although there is a considerable interindividual variation between songs recorded both in undisturbed and agonistic situations the A-song is shared between all studied territorial males (n = 6). There is also a close temporal connection between A-song and overt attack behaviour from the singer indicating that A-song transmit a message of an increased likelihood that the singer will attack his opponent. During a series of play-back trials when territorial males were exposed either to recordings of 'spontaneous song types or A-songs there was a marked tendency to approach the speaker as a response to spontaneous songs while A-songs instead evoked tendencies to withdraw. Thus, a test male responds to A-song and other song types in a manner which indicates that the message of an increased likelihood of an attack, following the former has been received.