Environmental change as a driver of the evolution of migratory behavior in suboscine birds

Avian migration, particularly long-distance seasonal migratory movement, has long captured the attention of researchers and the public alike. However, the evolutionary origins of migratory behavior are poorly understood, in part due to limited understanding of the full range of migratory strategies including short-distance and intra-tropical movements. We examine the climatic drivers of migration across suboscine birds, a group of roughly 1,300 primarily Neotropical species with a complex array of migratory strategies. Our reconstructions of the evolutionary history of suboscine migration reveal that migratory behavior is labile and is lost approximately twice as often as it is gained. We find that the evolution of migratory behavior in temperate-breeding, long-distance migrant suboscines is driven by temperature seasonality, presumably associated with departure from high latitudes to avoid resource drought in winter. Short-distance migration in tropical-breeding species, however, evolved in association with seasonality in precipitation. Tropical regions with high precipitation seasonality contain a mix of migrant and non-migrant suboscines, but a higher proportion of species vacates these areas compared to tropical regions with stable seasonal precipitation. Further, when we examine projected future climates under two scenarios, we find that while temperature seasonality is projected to decrease across the breeding ranges of most suboscines, precipitation seasonality demonstrates a more complex response that differs between future climate scenarios. The contrasting impacts of climate on the evolution of different migratory strategies highlights the complexity of climate-movement associations and the challenges associated with identifying how future climate change might impact organisms with disparate migratory strategies.