Morphological consequences of climate change for resident birds in intact Amazonian rainforest

Warming from climate change is expected to reduce body size of endotherms, but studies from temperate systems have produced equivocal results. Over four decades, we collected morphometric data on a nonmigratory understory bird community within Amazonian primary rainforest that is experiencing increasingly extreme climate. All 77 species showed lower mean mass since the early 1980s-nearly half with 95% confidence. A third of species concomitantly increased wing length, driving a decrease in mass:wing ratio for 69% of species. Seasonal precipitation patterns were generally better than temperature at explaining morphological variation. Short-term climatic conditions affected all metrics, but time trends in wing and mass:wing remained robust even after controlling for annual seasonal conditions. We attribute these results to pressures to increase resource economy under warming. Both seasonal and long-term morphological shifts suggest response to climate change and highlight its pervasive consequences, even in the heart of the world's largest rainforest.

Automated summary

Research conducted in the Amazonian rainforest over four decades shows that the body size of nonmigratory understory birds has decreased since the early 1980s, with some species showing an increase in wing length. Seasonal precipitation patterns were found to be better predictors of morphological variations than temperature. Both short-term and long-term morphological shifts suggest a response to climate change, reflecting its pervasive consequences.