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Abstract

The avian dawn chorus is a striking example of communication behavior that can have important consequences for the reproductive success of those participating. In this dissertation, I used a combination of observational, computational, and experimental approaches to examine the extent to which two singing behaviors, song type use and song overlapping, can function as signals and strategies during the dawn chorus. Splendid fairy-wrens (Malurus splendens), which breed cooperatively but exhibit high rates of extra-pair paternity, are an excellent system for investigating the functions of singing behaviors in both cooperative and competitive contexts. An analysis of the structure and propagation of splendid fairy-wren song revealed that, by appending a trill to the standard display song during the dawn chorus, a male may be able to increase the broadcast area and detectability of his performance, as well as its resistance to distortion. Song overlapping is a common occurrence during the dawn chorus of splendid fairy-wrens and the subject of a recent controversy; because individuals can sing simultaneously by chance, whether overlapping is intentional or accidental is often unknown. To address this issue, my collaborators and I developed the Song Overlap Null model Generator (SONG), a software package for R that uses resampling randomization to predict the expected amount of overlap in an interaction. Application of the SONG package revealed evidence that best supports the hypothesis that song overlapping functions as a masking strategy in splendid fairy-wrens; significant overlapping was observed between unrelated rivals, overlap avoidance occurred between related males, and the males with the largest cloacal protuberances and cloacal tips (traits that can increase the likelihood of successful fertilization) were overlapped at the highest rates. Together, trill use and song overlapping may represent a pair of signaling strategies by which a male can enhance the effectiveness of his performance, while diminishing the effectiveness of his rivals’ performances. This research contributes to our understanding of the signal value, and strategic value, of singing behavior, and further demonstrates how natural, social, and sexual selection can shape communication behavior.

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