
A Surprisingly Simple Explanation for the Shape of Bird Eggs - mhb
http://science.sciencemag.org/content/356/6344/1249.full
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achow
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.

