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.