Increasing climatic decoupling of bird abundances and distributions.

Abstract

Species abundances and distributions are changing in response to changing climate and other anthropogenic drivers but how this translates into how well species can match their optimal climate conditions as they change is not well understood. Using a continental-scale 30-year time series, we quantified temporal trends in climate matching of North American bird species and tested whether geographical variation in rates of climate and land use change and/or species traits could underlie variation in trends among species. Overall, we found that species abundances and distributions are becoming more decoupled from climate as it changes through time. Species differences in climate matching trends were related to their ecological traits, particularly habitat specialization, but not to average rates of climate and land use change within the species' ranges. Climatic decoupling through time was particularly prominent for birds that were declining in abundance and occupancy, including threatened species. While we could not discern whether climate decoupling causes or is caused by the negative population trends, higher climatic decoupling in declining species could lead to a feedback as birds experience increasing exposure to suboptimal climatic conditions.