Song-type switching rate in the chaffinch carries a message during simulated intrusion

Birds communicate their motivation and willingness to escalate a territorial conflict with a variety of agonistic signals. One of these, song-type switching, has been suggested to be a conventional signal in male–male interactions. However, this behavior does not show a consistent pattern across species. In this study, we asked whether variation in song-switching rate carries a message for song receivers among territorial chaffinches, Fringilla coelebs. Chaffinch song is well described, but only a few studies have focused on the communicative function of song-type switching or bout duration. Using data from playback experiments, we show here that variation in song-type switching rate affects the response of chaffinches. In response to the low switching rate treatment, territorial males began to sing later, produced fewer songs and more rain calls, decreased flight intensity, and spent more time close to the speaker than during playback of songs with a high switching rate. Our results provide strong evidence that the song-type switching rate is an agonistic signal in the chaffinch and that territorial males exhibit a stronger response toward rivals that sing with a lower song-type switching rate. A secondary purpose of our study was to determine the receivers’ response with respect to their own song rate and song repertoire. We found that the reaction of tested males was correlated with their own spontaneous song rate. This implies that a male’s response to stimuli may be predicted on the basis of his own song output.