Song type matching and vocal performance in territorial signalling by male swamp sparrows

In songbird species with repertoires of multiple songs, individuals in territorial interactions can engage in song type matching, in which one bird responds to another using the same song type. Song type matching is thought to be associated with aggressive intent, although empirical support for this hypothesis is mixed. Here we test the alternative hypothesis that males selectively use song type matching, depending on singing ability, to optimize their relative performance in a communication network. We recorded the responses of male swamp sparrows, Melospiza georgiana, to playback trials in which they heard stimulus songs of higher or lower vocal performance relative to their own version of those songs. We predicted that, if males use song type matching to influence the perceptions of conspecifics outside the interacting dyad, males would (1) match stimulus songs that they themselves could perform better and (2) respond with a different song type to stimulus songs that they could not perform as well. We found that males song-type matched more often than expected by chance across trials, but contrary to our expectations, they were at least as likely to match to playback of higher-performance songs as to playback of lower-performance songs. As in previous studies, we also found that males sang with higher vocal performance in response to playback than when singing spontaneously, and that they did not preferentially respond with their highest-performance song type as a countersinging strategy. Our results support the idea that in swamp sparrows, song type matching functions primarily within the dyad rather than to broadcast superior performance ability to other conspecifics in the communication network.