PMC

Measurement positions. The velvet‐like surface was investigated at four different parts of the wing (0.2, 0.4, 0.6 and 0.8 of wing length) which is indicated by the corresponding lines. Twelve chordwise measurement points were set at each investigated wing part. The first six measurement positions had a distance of 0.05 in the normalized x‐axis, between 0.05 and 0.3 of the normalized x‐axis. Measurement points between 0.4 and 0.9 were set in steps of 0.1 of the x‐axis. Note that samples were only taken from feather parts that exhibited the uncovered velvet‐like surface. The feathers that occur at these wing parts include marginal coverts, covert feathers (primary and secondary coverts) and flight feathers, depending on wing part and wing position.

Changes in wing shape across Aves. Ancestral state estimation for wing shape based on (a) ventral PC1 scores and (b) dorsal PC1 scores using weighted squared-change parsimony and the Jarvis et al. [] phylogenetic tree. Vector-based output was used to visualize how shape differed across the phylogeny. Each landmark of the consensus wing represents the vector base, and arrows show the direction and magnitude of variation at any point along the wing. Anseriformes, Podicipediformes, Charadriiformes and waterbirds (Aequornithia) show a trend towards more elongate primary covert feathers and shorter secondary feathers, regardless of flight style or body size. Core ‘higher landbirds’ show a trend toward shorter primary coverts.

Instantaneous values of wing surface area (a) and RTD (b). Black open circles, total (entire wing); black open squares, primary region; purple plus symbols, covert region (only in a); blue crosses, secondary region; red triangles, outer-primary region; orange diamonds, inner-primary region; green inverted triangles, mid-primary region; and grey filled circles, distance between p1 tip and s1 tip (only in b).

Dorsal (left) and ventral (right) wings show variation in relative covert length and geometric morphometric assessment of this variation. Representative taxa and specimens: (a) Spizella arborea, American tree sparrow; (b) Phalacrocorax auritus, double-crested cormorant; (c) Phoebastria immutabilis, Laysan albatross; (d) Aptenodytes patagonicus, king penguin; (e) Gavia immer, common loon. Pseudo-landmarks plotted on all wings in the study (f); consensus wing shape based on 105-taxa, 90 pseudo-landmarks (g); an example of vector-based output used to visualize how shape differed from the consensus wing (h). Each landmark of the consensus wing represents the vector base, and arrows show the direction and magnitude of difference at any point along the wing. Wings are not to scale.