Segregation of information in a complex acoustic signal: individual and dialect identity in white-crowned sparrow song

Many bird songs are highly complex acoustic signals that broadcast a variety of information over long distances. General explanations for signal complexity assume that either different signal components are redundant, or that each component conveys a different message. Puget Sound white-crowned sparrow, Zonotrichia leucophrys pugetensis, song consists of several temporally discrete phrases or components, two of which, the note complex and trill, vary independently across vocal dialects. Previous playback experiments with males suggest that the terminal trill encodes dialect identity. Here we test whether both the note complex and trill encode individual identity, as predicted by the redundancy hypothesis, or whether the note complex alone serves this role, as predicted by the multiple messages hypothesis. Analyses of acoustic variation in note complexes and trills, and results of a neighbour–stranger song discrimination playback experiment support the multiple messages hypothesis. Note complexes were more individually distinctive among males, and males responded stronger when a neighbour's song had a stranger's note complex substituted than when the neighbour's trill was replaced with that of a stranger. The segregation of cues to individual and dialect identity into the note complex and trill phrases, respectively, supports the hypothesis that coding conflicts may be resolved by using different song components for different functions.