Cryptic introductions and geographical patterns in bird color: Implications for the study of evolutionary divergence

In my dissertation I focused on several topics, two of which involve islands and another that follows logically from my work on islands: contemporary evolution and cryptic introductions, variation in island plumage coloration, and variation in plumage coloration within a lineage. I chose to work with the eastern bluebird (Sialia sialis) because it has an isolated island subspecies long thought to be endemic to Bermuda based upon striking plumage differences. In my first chapter I used microsatellite data to explore the origin and current status of this island population. Through my analysis I determined that the Bermuda subspecies represents one of the few known cases of a vertebrate cryptic invader that was likely introduced by humans approximately 400 years ago. Oceanic islands have a relatively recent history of human colonization and in the absence of paleontological or molecular evidence it should not be assumed that island species are native.;In both my second and third chapters I used avian perceptual modeling to deconstruct blue plumage coloration into four components (hue, chroma, percent UV, and brightness). In my second chapter, I used feathers from live birds to detail how color varied between island and mainland populations. I found significant differences in hue (shorter wavelengths) and increased brightness on Bermuda; showing rapid change over a short time frame. My work suggests that we need to define better what constitutes a ‘native’ species, especially in cases such as the eastern bluebird in Bermuda where there has been sufficient divergence in morphology to be classified as a subspecies.;My third chapter used museum specimens across the bluebird range to attribute specific color components to detectable differences between subspecies. Differences in percent UV and chroma accounted for most intraspecific variation. These components are thought to be condition dependent and may signify the importance of individual-level variation in phenotypic evolution. Furthermore, individual components did not vary in a coordinated manner, implying modularity between the mechanisms controlling color expression.