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Georgia Journal of Science

Article Title

TRILLED SONG TYPES ARE MORE SALIENT THAN NON-TRILLED SONG TYPES IN AGONISTIC INTERACTIONS BETWEEN MALE SONG SPARROWS (MELOSPIZA MELODIA

Abstract

In song sparrows, previous research has shown that full repertoire song indicates male quality. However, there has been little research devoted to understanding the functional significance of the various songs in a song sparrow’s repertoire. This study focused on trills to explore the possibility that repertoires evolved due to functional differences between songs based on structure. Trills have been the subject of much song research and are key message-carrying components likely to signal quality or aggressive intent of the singer. While most Song sparrow songs contain a trill, a small portion of songs do not. We conducted an experiment with 26 individuals on the campus of Western Carolina University. Trials featured six minutes of playback of either a trilled song type or nontrilled song type. Our response variable was average distance to the speaker as a measure of response intensity as per Searcy et al. (2006), with a lower average approach distance to the speaker characterizing the response as being more aggressive than a higher average approach distance. Our focal males approached more closely for the trilled songs (Paired T-test, P=0.04), supporting our hypothesis that song sparrows respond more intensively to trilled song types over nontrilled song types. This consistent difference in response intensity suggests that the song repertoire evolved not only as a signal of overall cognitive capacity, but to contain songs that can be used in various types of interactions. High trill performance is a correlate of mating success, so songs that lack trills may lack valuable cues for the receiver. This is indicated by not only higher average approach distances for the nontrilled songs, but larger standard deviations from those means as well. While trilled songs might be honest signals of quality and/or aggression, nontrilled songs may be attempts at novel, unmatchable songs, thus driving the evolution of repertoires.

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