Year-round behavioural and ecological influences on the function and evolution of ornamental plumage in migratory birds

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Bird migration has captivated researchers and natural historians for centuries, both because of its sheer magnitude and the incredible distances travelled. Take, for instance, the trans-continental journey of the Arctic tern, who travels yearly from its breeding grounds in the Arctic north to the Antarctic seas - a round-trip journey of nearly 30,000 kilometers. No less remarkable, however, is 24-hour trans-Gulf of Mexico flight of the diminutive ruby-throated hummingbird. These migratory journeys are staggering in both number and duration, with billions of individuals traveling thousands of kilometers every year. For researchers studying migratory birds, a major challenge is understanding the evolution and ecology of these birds when, despite the vastness and ubiquity of the phenomenon, we still know little about the factors that influence their life history and behaviour outside of the breeding period. Indeed, the vast majority of our knowledge of migratory birds comes from studies conducted on the temperate breeding grounds in Eurasia and North America, with very few studies addressing the over-wintering and migratory ecology of migratory birds. Yet, new technologies for tracking individuals throughout the year offer promising avenues for future research on the behaviour and ecology of migratory birds. For example, stable-isotopes (stable forms of elements such as C, N, and H that vary predictably in the environment and travel up the food chain to be incorporated in bird tissues) in bird feathers and claws can help determine the location of moult or the quality of habitat a bird spent the winter in. Additionally, backpack-style devices, such as light-level geolocators (data loggers attached to the birds that record ambient light levels) are allowing researchers estimate individual latitude and longitude over the yearly journey. In this study, I aim to examine the function and evolution of colourful ornamental plumage in migratory birds throughout the year and across continents. This work will be the first to combine stable isotope analysis with light-level geolocators to study how events occurring throughout the annual cycle influence the evolution of ornamental plumage colouration in free-living migratory birds.