Excerpt: Adaptations for flight may be key drivers of egg-shape variation in birds. Key adaptations for high-powered flight—including reduced body size, a red

Excerpt: Adaptations for flight may be key drivers of egg-shape variation in birds. Key adaptations for high-powered flight—including reduced body size, a reduced abdominal cavity, and the loss of a functional ovary and oviduct—may have considerable effects on egg shape. Such adaptations place constraints on the maximum size or width of a stretched oviduct, which in turn can be accommodated by increasing ellipticity and/or asymmetry of eggs to increase egg volume while maintaining or reducing girth. We propose that general adaptations for strong flight select for a constrained, muscular, streamlined body plan giving rise, directly or indirectly, to asymmetric and/or elliptical eggs.