Behavioral Information Provided By Two Song Forms of the Eastern Kingbird, T. Tyrannus

Abstract Eastern kingbirds facilitate prediction of their social behavior through the proportional use of two different song forms, zeer and chatter-zeer, in daytime singing performances. The chatter-zeer song form predicts approach to closer quarters, whereas zeer predicts a high probability of staying put. The correlations of each song form with behavior were determined by observing natural encounters singers had with their mates, conspecific intruders and birds of other species. Playback simulations of territorial intrusions were then used to test whether singers would approach with a high proportion of chatter-zeer and little or no zeer. This was strongly confirmed. Kingbirds who approach are taking a major interactional initiative, even though their next move is usually to await the other individual's response. In effect, singers dare or encourage those individuals to interact. The chatter-zeer with which they precede or announce approach does not specify the kind of interaction for which singers are prepared: the information it provides is as relevant in events in which the singer associates with its mate as in events in which the singer confronts an opponent. A zeer singer is less actively provocative, deferring initiative more while nonetheless being ready to respond to the actions of others. By providing information about the relative probabilities of these actions, singing should help kingbirds to negotiate or even arrange social issues while spatially separated, often obviating closer encounters. Since many kinds of animals sing, and since the characteristic continuity and cadencing of singing performances are specializations well suited to communicating at a distance, it is worth asking if other species also use singing patterns and songs to distinguish between the actions of holding back and approaching.