Fig. 2: A bird’s centre of gravity is minimally affected by elbow and wrist flexion and extension.
From: Birds can transition between stable and unstable states via wing morphing
a, Time-calibrated phylogeny for 22 species (mya, million years ago). b, c, The elbow and wrist ROM (opaque polygons, convex hulls) affect \({x}_{\bar{{\rm{C}}}{\rm{G}}}\) and \({z}_{\bar{{\rm{C}}}{\rm{G}}}\) (over bar indicates normalization by body length) (b) and \({y}_{{\bar{{\rm{C}}}{\rm{G}}}_{{\rm{w}}{\rm{i}}{\rm{n}}{\rm{g}}}}\)(over bar indicates normalization by maximum half span) (c). b, The centre of gravity range is overlaid with the maximum bounds due to 90° shoulder rotation (transparent polygons), (d) which increase with increasing ratio of wingspan to body length. e, Effect size (partial η2) of elbow, wrist, and interaction on each centre of gravity component per specimen. f, g, The log-transformed mean values of \({x}_{\bar{{\rm{C}}}{\rm{G}}}\) and \({z}_{\bar{{\rm{C}}}{\rm{G}}}\)* (*denotes the z position relative to the dorsal origin defined by Fig. 1c) (f) and \({y}_{{\bar{{\rm{C}}}{\rm{G}}}_{{\rm{w}}{\rm{i}}{\rm{n}}{\rm{g}}}}\) did not scale with body mass as the phylogenetic generalized linear mixed model (PGLMM) (solid line) did not differ significantly from the null slope (dashed line). n = 36 individual specimens; 95% confidence intervals visualized in d, f, g by transparent ribbons.
