Genetic variation reveals individual-level climate tracking across the full annual cycle of a migratory bird

Adaptation across climate gradients can provide the raw material needed for evolutionary response to climate change. In migratory species, studies of local climate adaptation are made challenging by seasonal movement, where it is unclear to what extent individuals track their local climate niches across the annual cycle. In the migratory songbird yellow warbler (Setophaga petechia), we test the hypothesis that individuals track similar climates between their breeding and wintering ranges. Further, we examine whether adaptation to local climate might lead to morphological differences among populations and different demographic responses to temporal climate variability. We find a correlation between wintering and breeding precipitation but not temperature regimes at the level of the individual bird. Specifically, birds from the driest wintering regions migrate to the driest breeding regions. Additionally, we find an association between bill size and breeding season precipitation which, given documented climate-associated genomic variation, suggests adaptation to local precipitation gradients might exist on the breeding grounds. Finally, we show geographic variation in the effect of precipitation on demography, with higher precipitation associated with population increases in some regions and declines in others. Taken together, our results suggest that variation in climate optima exists across the breeding range of yellow warblers and provide a potential mechanism for parallel selection across the annual cycle.