Age-Related Variation in Wing Shape Differs between Bird Orders: Implications for Interpretation of the Pointedness Index (C2 Axis) in a Size-Constrained Principal Component Analysis (SCCA)

Summary. There is a strong relationship between bird wing morphology and flight style. Wing shapes are related to manoeuvrability, flight speed, energetic costs during flight and take-off speed. Wing shape differences among species have been frequently studied but differences can also be found within species, between sexes and age groups. Many studies have assessed differences in wing shape between juveniles and adults in different passerine species but little is known about such differences in other bird orders. Performing a Size Constrained Components Analysis (SCCA) and a graphical approximation, we analysed the wing shape of juveniles and adults of eight species, including four passerines and four non-passerines of three different orders. According to a graphical approximation, we observed that wing shape differences between age groups differ among species. In the non-passerine species considered, juveniles have more pointed and concave wings than adults. In contrast, in the four passerine species, juveniles have more rounded wings than adults. However, the results for the C2 axis of SCCA (index of pointedness) do not completely agree with the graphical approximation. Our results showed that the C2 axis does not represent the same vector of wing shape variation in all species. The contribution of changes in C2 to variation in wing pointedness seemed to depend on the position of the wing tip, which is a good index of pointedness only when the wing tip is in the two most distal primary feathers. Surprisingly, the adults of some species do not have longer wings than the corresponding juveniles, because the feathers that define the wing tip do not grow longer during the first complete moult. We discuss the role of the first complete moult in changing the shape of juvenile wings into adult wings, and the implications of our results for the analysis of bird wing shape.—Cabodevilla, X., Pérez-Tris, J., Moreno-Zarate, L., Pérez-Rodríguez, A., Lima-Barbero, J.F., Cruz Camacho, M., Villanua, D., Ibáñez, R., Gerboles, A. & Arroyo, B. (2020). Age-related variation in wing shape differs between bird orders: implications for interpretation of the pointedness index (C2 axis) in a size-constrained principal component analysis (SCCA). Ardeola, 67: 341-354.