Abstract
One hypothesis for the function of vocal repertoires in songbirds is that singing multiple song types facilitates song matching, a behaviour in which one male replies to a rival's song with a song of the same type. In eastern populations of song sparrows, low levels of whole song sharing restrict opportunities for matching of entire song types. A male in this population might still match a neighbour by replying with a partially shared song (i.e. a song that contains one or more phrases in common with the neighbour's song). We tested for partial matching in a Pennsylvania population using playback of three categories of song: self song (allowing a full match), stranger song (a control allowing no match) and hybrid self/stranger song (allowing a partial match). We also tested the hypothesis that matching is a directed signal of aggressive intentions by comparing subjects' approach distances between trials in which they did and did not match. Males in our study matched in response to both self song (21 of 39 trials) and hybrid song (23 of 40 trials) at levels significantly greater than expected based on control trials (5 of 40 trials). Males that performed a partial match to a hybrid song approached the speaker more closely than males that did not match, consistent with the hypothesis that partial matching is a directed signal of aggression. Self song matching did not predict approach as successfully.
