Three vocalization types in the blue tit Cyanistes caeruleus: a test of the different signal-value hypothesis

Abstract

Many songbird species use a repertoire of different song types in close-range interactions. In male blue tits, Cyanistes caeruleus, this includes songs with and without trill as well as scolding-like vocalizations. We here investigate using playback experiments whether these vocalization types are used at different stages during aggressive interactions, which may be reflected in differential responses of receivers. We predict that territory owning receivers will vary their strength of response with the vocalization type of a simulated intruder and that an aggressive territorial response may include song type matching, i.e. the use of the same vocalization type as the intruder. Supporting the different-signal value hypothesis, scolding-like playback elicited a stronger approach response of focal males than playback of songs with or without trill. There was no difference in song rate nor do songs without trill elicit a different strength of response than songs with trill. Males did not differ significantly in the amount of song type matching between the treatments but males that landed on the loudspeaker with playback of either songs without trill or scolding-like vocalizations did not match playback songs at all. This suggests a trade-off between approach and song type matching where song type matching is superfluous during very close approaches. Our results may suggest that in the blue tit threat display may be graded from songs with or without trill to scolding-like vocalizations and eventual attack of an intruder.