Migration Evolves in Response to Distinct Regimes of Climate Seasonality in Tropical Versus Temperate-Breeding Suboscine Birds.

Avian migration has long captured human interest, but the causes of the evolution of migration remain unclear due to limited study of the full spectrum of migratory strategies, including short-distance and intratropical movements. We examine the climatic drivers of migration across the roughly 1300 species of suboscine birds, a group containing many intratropical migrants. Comparative analyses confirm that migratory behavior in temperate-breeding suboscines evolves in association with temperature seasonality. The evolution of migration in the tropics, however, has a more complex association with climatic variables including precipitation and greenness seasonality. Projections under future climate scenarios show that suboscines will experience average lower temperature seasonality, potentially favoring the loss of migration, but higher precipitation seasonality, potentially favoring an increase in short-distance migration. The divergent impacts of climate seasonality on the evolution of different migratory strategies highlight the complexity of climate-movement associations and the challenges of projecting responses to climate change.