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How invasive species establish and spread is a central question in biology, but also one that impacts public perceptions of and engagement with those species. I use the invasive European starling (Sturnus vulgaris) as a case study to identify factors supporting its establishment and expansion in the United States, and to consider its evolutionary history in its native range. In my first chapter, I integrate recent work in the evolutionary genetics of invasive European starling populations with ecological studies over its residence in each region, identifying areas for future research. In my second chapter, I use genomic methods to reconstruct demographic history and test for natural selection in the North American invasion, and I find that starlings in North America show evidence for local adaptation despite a genetic bottleneck upon invasion. In my third chapter, I compare patterns of genetic variation between the concurrent North American and Australian invasions: starling populations show remarkably high differentiation from each other on a short evolutionary timescale, and this differentiation is consistent with selection in at least a few regions of the genome. In my fourth chapter, I consider starling invasions from the perspective of science and technology studies (STS), tracing where human interference and potential biases shape both the practice of invasion science. I consider how my own genomic analyses depend on assumptions in both population genetic methods and invasion theory. Overall, this dissertation attempts to reconstruct the evolutionary history of starling invasions, with a focus on the invasion in North America.

Vocal learning is an ability that has only evolved in a handful of taxa. Songbirds learn their songs, and some species have flexible learning in which they not only incorporate species-specific sounds, but heterospecific and/or environmental sounds as well. The functions of vocal mimicry are still unknown for many species and studying mimicry can teach us about the variation within the song learning process. In this thesis, I focused on five hypotheses on how mimicry could function in sexual selection. The repertoire size hypothesis suggests that selection for larger repertoire sizes allows mimicry to occur because imitation can increase repertoire size. The permissive learning hypothesis states that heightened song complexity requires a relaxed song template, which may allow passive use of mimicry. The learning and performance hypothesis suggests that learning ability and song or performance quality are honest signals of a singer’s quality and that listeners may focus on mimicry to assess individuals. The fourth and fifth hypotheses, which have received very little attention, are the structural function and acoustic function hypotheses, which suggest that mimicry has an as-yet-unknown structural or acoustic role in song, respectively. In these cases, mimetic accuracy does not matter; rather imitations and species-specific vocalizations are used in different ways. I explored these hypotheses using European starling (Sturnus vulgaris) song. Instead of testing the evolutionary functions of mimicry directly, I concentrated on the structural mechanics of mimicry in song. This approach allowed me to indirectly test whether mimetic and nonmimetic song components have the same functional effect. Chapter I is an overview of the more than 300 songbird species that are vocal mimics and shows that mimicry evolved repeatedly throughout the evolution of the songbird clade. The next three chapters are a detailed case study of the vocal mimicry of European starlings. In chapters II through IV, I use a combination of structural and acoustic analyses to emphasize the ways in which mimicry functions in starling song. I show that mimicry is treated differently from species-specific sounds, although in subtle, structural ways, and it remains unclear how important the inclusion of mimicry is to listeners. Advisor: Daizaburo Shizuka