First Advisor

Lauryn Benedict

Degree Name

Master of Science

Document Type


Date Created



Bird song has been studied extensively as a model of complex animal communication systems because of how various and flexible it is in certain species. Numerous researchers have investigated the evolutionary pressures leading to the elaboration of songs available in a bird’s repertoire and this topic is most often evaluated in light of sexual selection. Intersexual selection mechanisms such as female choice are often presumed to be very important in the elaboration of song, however literature reviews on the topic find no strong correlation between female preference for larger song repertoires and the presence of the characteristic in males across all species. Another important aspect of sexual selection not often examined in regards to avian song elaboration is intrasexual selection mechanisms such as territory defense and within-sex competition. In no single study were both mechanisms of selection on a trait evaluated within the same individuals, though some studies have independently looked at both aspects in the same species. In this study I evaluated the function of song type repertoire size in a monomorphic species, the Rock Wren, in light of both inter- and intrasexual selection. To test the function of song type repertoire in territory defense contexts, I performed playback experiments to focal male Rock Wrens and assessed their response patterns to both large and small repertoire sizes. Males responded more strongly to tracks playing large song repertoires by singing faster in response and singing more songs. They also sang shorter songs that had lower frequencies and broader bandwidth. To evaluate inter-sexual selection pressures on repertoire size, I followed males throughout the breeding season to assess various proxies of female choice, including first egg lay date, clutch size, fledge count, and male prey delivery rate. None of the measures of female choice that I evaluated were related to her mate’s repertoire size. I conclude that song repertoires must be more important for assessing rival males in territory defense scenarios than for assessing potential mates in this species. These results support intrasexual competition as an important mechanism of selection that can lead to the elaboration of communication signals in bird species, and demonstrate that elaboration of song is not necessarily driven by mate choice dynamics. Intrasexually selected increases in repertoire size provide an alternative mechanism to female choice generating complexity for animal signaling systems.

Abstract Format



127 pages


Dean's Citation for Excellence

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Copyright is held by the author.