Long- and short-term responses to climate change in body and appendage size of diverse Australian birds

Changes to body size and shape have been identified as potential adaptive responses to climate change, but the pervasiveness of these responses has been questioned. To address this, we measured body and appendage size from 5013 museum bird skins of 78 ecologically and evolutionary diverse Australian species. We found that morphological change is a shared response to climate change across birds. Birds increased relative bill surface area, tarsus length, and relative wing length through time, consistent with expectations of increasing appendage size as climates warm. 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 and migratory and thermoregulatory behaviors. Shorter term responses to higher temperatures were contrary to long-term effects for appendages, wherein relative appendage size decreased after hotter years, indicating the complex selective pressures acting on birds as temperatures rise with climate change. Overall, our findings support the notion that morphological adaptation is a widespread response to climate change in birds that is independent of other ecological traits.