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Egg Shape

June 26, 2017

An exhaustive analysis of birds and their eggs may explain why eggs vary in shape.



Bird eggs come in a vast array of sizes and shapes. (Illustration by Adolphe Millot, from Nouveau Larousse Illustré,1897-1904)


How eggs got their shapes. I’m Bob Hirshon and this is Science Update.

Bird eggs vary in shape, from the owl’s nearly spherical ping pong ball eggs to the tear-drop shaped eggs of the sandpiper. Did the shapes evolve because of diet, or maybe nesting behavior? In the journal Science, Princeton evolutionary biologist Mary Caswell Stoddard and her colleagues report that the key factor is flying ability.

MARY CASWELL STODDARD (Princeton University):

We found that birds that are good fliers tend to lay eggs that are more elliptical or more asymmetric. We think that as birds’ bodies became streamlined for powerful flight, this may have influenced the internal organs in a way that ultimately affect this process of egg shaping.


Scientists have long been fascinated with the evolution of the egg which was a milestone in vertebrate history, allowing reptiles and then birds to colonize land. I’m Bob Hirshon, for AAAS, the science society.

Story by Bob Hirshon