Pervasive morphological responses to climate change in bird body and appendage size

Changes to body size and shape have been identified as potential adaptive responses to climate change, but the pervasiveness of these responses is questioned. To address this, we measured body and appendage size from 5013 museum bird skins of ecologically and evolutionary diverse species. We found that morphological change is a shared response to climate change across birds. Birds increased bill surface area, tarsus length, and relative wing length through time, consistent with expectations of increasing appendage size in warmer climates. Furthermore, birds decreased in absolute wing length, consistent with the expectation of decreasing body size in warmer climates. Interestingly, these trends were generally consistent across different diets, foraging habitats, and migratory and thermoregulatory behaviours. Shorter-term responses to hot weather were contrary to long-term effects for appendages. Overall, our findings support that morphological adaptation is a widespread response to climate change in birds that is independent of other ecological traits. ### Competing Interest Statement The authors have declared no competing interest.