Data for: Altered wing phenotypes of captive‐bred migratory birds lower post‐release fitness

Captive-breeding and release to the wild is a globally important conservation tool. However, captivity can result in phenotypic changes that incur post-release fitness costs, especially if they affect strenuous or risky behaviors. Bird wing shape is critical for migration success and suboptimal phenotypes are strongly selected against. I demonstrate surprising plasticity of bird wing phenotypes in captivity for 4/16 studied species. In a model species, captive-born juveniles with wild wing phenotypes (a 1mm longer distal primary flight feather) survived post-release at 2.7 times the rate of those with captive phenotypes (i.e. a shorter distal feather). Subtle phenotypic changes and their fitness impacts are more common than widely realized because they are easily overlooked. To improve captive-breeding for conservation, practitioners must surveil phenotypic changes and find ways to mitigate them.