Long-Term Drought Exposure Shapes Declines and Range Shifts in Aridland Birds

Abstract

Climate change increases drought frequencies and intensities, posing risks to biodiversity. Species inhabiting arid regions may be vulnerable to drought because they live near their physiological limits, while species with low historical drought exposure may lack adaptations to cope with unprecedented drought. Using a breeding bird dataset and the Standardized Precipitation-Evaporation Index, we assessed drought vulnerability of 37 bird species across deserts of the western United States. We tested drought effects on community and species-level relative abundance, how species’ long-term drought exposure influences these effects, and for drought-induced range shifts. Drought was associated with abundance declines and distributional shifts for over 40% of species, with shift directions reflecting regional drought patterns. Species with lower historical drought exposure declined more strongly, though several highly exposed species were among the most vulnerable. These findings demonstrate that climatic history modulates species’ responses to increasing aridity. Under intensifying drought, incorporating regional drought dynamics and climatic legacies into climate change vulnerability assessments is essential for anticipating conservation issues.