Date of Award


Degree Name

Master of Science


Biological Sciences

First Advisor

Dr. Sharon Gill

Second Advisor

Dr. Maarten Vonhof

Third Advisor

Dr. Tiffany Schriever


Golden-wing warbler, blue-winged warbler, song, behavioral isolation, reproductive barriers

Access Setting

Masters Thesis-Open Access


Reproductive isolation mechanisms such as song are used by birds to promote assortative mating by species and prevent gene flow when closely related species come into secondary contact. Based on the strength of a reproductive barrier, signals in hybrid zones can diverge and become more dissimilar to maintain species or converge to become more similar and make species discrimination more difficult. When two closely related species overlap in territories and have similar songs, song convergence is likely and has the capacity to disrupt species recognition. We test the hypothesis that song acts as a reproductive isolation mechanism by examining song variation and species discrimination in a population of hybridizing golden-winged (Vermivora chrysoptera) and blue-winged warblers (V. cyanoptera). Singing male winged warblers were recorded and acoustic trait data were quantified to assess the degree of song variation. We use playback experiments to measure male responses to simulated intrusions of conspecific, heterospecific, and atypical songs. We also measure whether the plumage, genetics, or song of males predicts their responses to playback stimuli. Songs from the contact zone of winged warblers separate into three distinct song groups showing considerable variation and evidence for songs other than the typical winged warbler songs. Playback experiments reveal weak species discrimination of winged warbler stimuli as males responded through movements and vocalizations to all three playback stimuli. Song convergence and weak species discrimination indicate the breakdown of an important reproductive barrier.