Author Type

Graduate Student

Date of Award

Spring 4-11-2026

Document Type

Dissertation

Publication Status

Version of Record

Submission Date

April 2026

Department

Biological Sciences

College Granting Degree

Charles E. Schmidt College of Science

Department Granting Degree

Biological Sciences

Degree Name

Doctor of Philosophy (PhD)

Thesis/Dissertation Advisor [Chair]

Rindy C. Anderson

Abstract

Birdsong is a communication signal shaped by ecological, morphological, and cultural processes. While many songbird species produce relatively simple vocal repertoires, others, such as the Bachman’s Sparrow (Peucaea aestivalis), produce moderately large repertoires with multiple distinct and context-dependent song categories. Despite this complexity, little is known about the major drivers that shape song elaboration in this species. Additionally, it is unclear whether abiotic factors play a significant role in determining how different song types are learned and shared within a population. To better understand how ecological and social pressures shape song variation, I conducted three studies using Bachman’s sparrows as a model. Male Bachman's sparrows have, on average, 48 “primary” song types in their repertoires, which function to attract mates and repel rival males. In addition, close to 50% of these song types are shared among males. Some song types are highly shared and sung by many males in the population, while others are rare and sung by very few males. I conducted song propagation experiments to test the hypothesis that song type sharing is influenced by the propagation properties of individual song types, leading to differential learning rates of those song types within a population. I also tested whether additional abiotic factors, such as wind speed, height, and tree density, affected the propagation properties of common and rare song types differentially in Bachman’s sparrows. My results indicate that rare song types significantly propagate less effectively compared to common ones, but the effect is relatively small. Other factors, such as sexual selection, likely have a greater influence on the distribution of common and rare song types among males within a population.

Next, to test for relationships between different male qualities and vocal performance features of complex songs, I captured male Bachman’s sparrows and took morphological measurements, photographed wing-epaulet ornamentation, and recorded complex songs from each subject. Then, I tested for relationships between body size, epaulet coloration, and vocal performance of complex songs using general linear mixed models. Results showed both support and opposition to my predictions. Males that weighed less but were larger in skeletal size sang complex songs with higher performance. In addition, males with more pronounced epaulet coloration sang more complex songs with higher performance. Finally, to examine whether complex song serves as an intrasexual signal in male Bachman’s sparrow, I tested for differences in responses from territorial males across three song categories (primary, whisper, and complex). I conducted behavioral assays to test the hypothesis that complex songs elicit a higher aggressive response from territorial males than primary or whisper songs. Results showed that complex songs elicited a stronger response from territorial males using a composite measure of agonistic behaviors. Specifically, territorial males flew more frequently, sang more whisper songs, and stayed closer to the simulated intruder in response to complex song playback. The results of my dissertation provide novel insights into the effects of habitat-related degradation on common and rare song types, the social function of an enigmatic category of song, and the identification of information about male quality that is encoded in the performance of complex songs.

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