Song‐type function during territorial encounters in male Cetti's Warblers Cettia cetti

Abstract

During undisturbed singing, male Cetti's Warblers Cettia cetti sing constantly the same song type (S‐song), which is stereotyped individually but differs between individuals. When facing a territorial dispute, males may start to sing a distinct song type (I‐song) used only in this context. To evaluate the functional significance of these two song types in the communication system of Cetti's Warbler, two series of playback experiments were performed. When exposed to repeated S‐songs of an extraneous male, most of the ten birds tested ceased to sing S‐songs and used I‐songs, generally while displaying aggressive reactions. After a while, they started to sing S‐songs again but at a higher rate than before the playback. In a second series of experiments, seven birds were first exposed to a playback of S‐songs and then to a second stimulation with three I‐songs or with three further S‐songs. The birds tended to approach the speakers in response to the first playback but, in most cases, withdrew from them after the second one. No significant differences in the reactions of the test birds were found between the trials using S‐songs and those with I‐songs. The present results indicate that the two song types constitute two signals associated with territorial behaviour; the song type emitted is probably dependent on the singer's level of aggressiveness.