Quantifying avian wing shapes: Evaluating indices, their relationships, and ecological correlates

Avian wings are central to their remarkable flight ability and diverse life history strategies, including behaviors such as fighting and mating. These multifaceted functions are intricately tied to wing shape, which varies significantly across species because of the complex interplay of evolutionary and ecological pressures. Many indices have been developed to quantify wing characteristics to facilitate the study and comparison of avian wing morphology across species. This study provides a comprehensive overview of existing quantitative methods for analyzing avian wing shapes. We then constructed a new quantification framework through the beta distribution, which can generate indices reflecting the shape of avian wings (center, dispersion, skewness, and kurtosis). Next, we used the flight feathers of 613 bird species to perform different quantitative analyses and explore the relationships between various wing shape quantification methods and life history traits, which serve as proxies for the selective forces shaping wing morphology. We find that the wing shape indices are more strongly associated with ecological variables than with morphological variables, especially for migration, habitat and territoriality. This research guides the selection of appropriate methods for wing shape analysis, contributing to a deeper understanding of avian morphology and its evolutionary drivers.