Carry-over effects in American redstarts: Implications for sexual selection and behaviour
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Migratory birds spend most of the year on the over-wintering grounds or traveling between breeding and wintering areas, but research has focused on the relatively short breeding period. As a consequence, we have only a rudimentary understanding of how life histories of long-distance migrants are shaped by events and selective pressures interacting throughout the annual cycle. In this thesis, I examine the association between plumage traits and performance, both during the over-wintering and breeding phases of the annual cycle and how events during one season carry-over to influence behavioural and evolutionary processes in subsequent seasons in a migratory warbler, the American redstart (Setophaga ruticilla). First, I demonstrate that tail feather brightness is correlated with winter habitat quality in Jamaica, suggesting that plumage may act as a status signal during the non-breeding season. Stable-carbon isotopes analyzed from claws of redstarts arriving on the breeding grounds confirm the association between ornamentation and winter territory quality. Second, I demonstrate that redstarts arriving to breed in southern Ontario from high-quality winter habitats arrive earlier, resulting in a lower probability of paternity loss, a higher probability of achieving polygyny, and higher genetic fledging success. Third, I demonstrate that tail feather brightness, associated with winter territory quality, predicts the likelihood of polygyny during the breeding season, indicating that tail brightness is associated with performance during two phases of the annual cycle. Paternity is predicted by both tail and flank colouration. Finally, I demonstrate that reported trade-offs between reproductive effort and plumage ornamentation as manifested by moult-migration in redstarts is likely an artifact of high variation in local stable-hydrogen isotope signatures (δD) and occasional feather loss and re-growth during the over-wintering period. Thus, moult-migration does not appear to be an important carry-over effect in redstarts. This work demonstrates that plumage may be under selection during both stationary phases of the annual cycle. Furthermore, it suggests that carry-over effects from the non-breeding season can influence evolutionary processes such as sexual selection and highlights the importance of considering selective pressures and events occurring throughout the annual cycle in studying the behaviour and ecology of migratory animals.