The role of tropical rainfall in driving range dynamics for a long-distance migratory bird

Predicting how the range dynamics of migratory species will respond to climate change requires a mechanistic understanding of the factors that operate across the annual cycle to control the distribution and abundance of a species. Here we use multiple lines of evidence to reveal that environmental conditions during the nonbreeding season influence range dynamics across the lifecycle of a migratory songbird, the American redstart (Setophaga ruticilla). Using long-term data from the nonbreeding grounds and breeding origin estimated from stable hydrogen isotopes in tail feathers, we found that the relationship between nonbreeding season survival and migration distance is mediated by precipitation, but only during dry years. A long-term drying trend throughout the Caribbean is associated with higher mortality for individuals from the northern portion of the species’ breeding range, resulting in an approximate 500 km southward shift in breeding origins of this Jamaican population over the past 30 years. This shift in connectivity is mirrored by changes in the redstarts breeding distribution of abundance. These results demonstrate that the climatic effects on demographic processes originating during the tropical nonbreeding season is actively shaping range dynamics in a migratory bird.

Methods
See the manuscript and supplementary materials for further details on model formulation. The data included here include BBS and environmental data for the abundance and occupancy analysis. Geolocator data can be found in https://doi.org/10.1002/ecy.3938.