Seasonal interactions in the Yellow Warbler (Setophaga petechia): winter habitat use, migration and demography

Numerous bird species in the western hemisphere – Nearctic-Neotropical migrants – breed and rear young in North America but spend two-thirds of the year south of the Tropic of Cancer. The annual cycle of these species can be divided into a distinct breeding, migratory and non-breeding period. Events in one period may alter demographic rates in a subsequent period; however, the spatial and temporal separation of these events and the difficulty of tracking individuals over the annual cycle make detecting seasonal interactions/carry-over effects difficult. In this thesis I confirm that δ13C and δ15N isotopic signatures in Yellow Warbler (Setophaga petechia) tissues vary with winter habitat use and can therefore be used as a means of inferring the wintering conditions experienced by individuals captured on the breeding grounds. I show that isotopic signatures suggestive of drier and possibly more southerly winter habitat use are associated with delayed clutch initiation and lower productivity in young female Yellow Warblers breeding in Revelstoke, British Columbia. In contrast, wintering isotopic signatures do not influence the breeding phenology of other age/sex-classes in Revelstoke or any age/sex-class in Inuvik, Northwest Territories, 2000 km further north. Differences between Revelstoke and Inuvik in how productivity declines seasonally suggest that one pathway through which carry-over effects can act is reduced or absent in the north. I also examine the role of climate variables operating at discrete periods of the annual cycle on the demography of Yellow Warblers in Revelstoke. I demonstrate that wind conditions during spring migration are the best predictor of adult survival, male arrival date and female clutch initiation date. These timing effects, in turn, impact reproductive success. This finding indicates that the spring migration is a key period for western Yellow Warblers, having a larger impact than either winter habitat use or wintering conditions and influencing both demographic rates.