The eggs of birds that are airborne most of their lives—murres, sandpipers, albatrosses—are elliptical, the theory goes, streamlined to fit through the pelvis of the birds’ smaller, lighter, and more compact skeletons. Owls, which tend to fly only in short glides, have a heavier skeleton and a wider pelvis that can accommodate more spherical eggs. (But there are exceptions, of course. Barn owl eggs are decidedly conical or ovoid. The eggs of Great Grays are “egg-shaped,” too, but they’re smaller than a hen’s egg and can fit through the bird’s pelvis.)
