Abstract/Summary

The Common Grackle Quiscalus quiscula is an abundant, widespread New World blackbird (Icteridae) described by Linnaeus in 1758. The bulk of the taxonomic and nomenclatural work on this species was done by Frank M. Chapman and other American luminaries of ornithology such as Witmer Stone, Robert Ridgway, Harry C. Oberholser, and Alexander Wetmore between 1892 and 1940. Since 1957, the Common Grackle has been considered a single species comprised of three subspecies: quiscula, versicolor and stonei. A third form Q. q. ridgwayi was described but is a hybrid between forms. Research on this taxon after 1940 focused on ethology and agricultural concerns but Charles E. Huntington, Suh Y. Yang and Robert K. Selander raised important questions regarding the formal taxonomic nomenclature of this species in 1952 and 1968, respectively. This study is a continuation of the work on Common Grackles, to better understand their phylogeographic and biogeographic history, and recommends modifications to the currently accepted status of subspecies. Chapter 1 is an overview of North American icterids in general and the Common Grackle specifically; it reviews the life history of the species and discusses the research questions and experimental protocols employed. Chapter 2 uses mtDNA analysis, and statistical techniques, unavailable to early researchers, to assess and confirm various aspects of past results and provides novel information about the relationship between Common Grackle subspecies. Chapter 3 analyses past descriptions of plumage characters considering the results in Chapter 2 and bolsters the result that the ‘Florida’ Grackle is ancestral and that only two subspecies (quiscula and versicolor) should be recognized. Using ecological modelling techniques, Chapter 4 demonstrates that the ancestral form of Common Grackle was confined to a single south-eastern refugia during the Last Glacial Maximum 22,000 years ago, not two separate refugia as hypothesized by Chapman. Chapter 5 uses an ecological niche modelling approach that suggests increasing temperatures might precipitate a significant westward expansion of this species in the future. Lastly, Chapter 6 discusses the main findings and contributions of this research and suggests future lines of inquiry into this intriguing North American passerine bird.