Wing pointedness associated with migratory distance in common-garden and comparative studies of stonechats (Saxicola torquata)

Migration promotes utilization of seasonal resources, and the distance flown is associated with specific morphologies, yet these relationships can be confounded by environmental factors and phylogeny. Understanding adaptations associated with migration is important: although migration patterns change rapidly, it is unclear whether migratory traits track behavioural shifts. We studied morphometrics of four stonechat populations representing a migratory gradient and raised under common-garden conditions. With multivariate analyses, we identified wing traits that differed clearly from general size trends, and used phylogenetic comparative methods to test the prediction that these traits correlated with migratory distance in captive and wild populations. Pointedness differed among populations, changed independently from overall body size, and was correlated with migration distance. Migration in stonechats may lead to deviations from allometric size changes, suggesting that birds may adapt morphologically to selection pressures created by their own behaviour in response to changing environmental conditions.