Life Lines by Dr. Dolittle

Sponsored by the American Physiological Society

How bird eggs got their shape

bird eggs

Image of a variety of bird eggs from Internet Archive Book Images, via Wikimedia Commons

Ever wonder why bird eggs are shaped the way they are and what drives the variations in egg shapes across species? I never really wondered that either until I saw an article in Science that explained a possible reason…then I just HAD to know. Some theories had been proposed suggesting that their shape prevented eggs from rolling out of nests or otherwise sustaining damage, and so on. According to the new study, the shape of a bird’s eggs may be related to their ability to fly. Researchers compared how elliptical, spherical and asymmetrical 50,000 eggs from 1400 species were. What they discovered is that eggs from species that are strong fliers were more elliptical or asymmetrical. They proposed that the reproductive tract of these birds may have become more narrow, thus leading to the elongated shape of their eggs. It should be noted that not everyone is convinced by this explanation and variations certainly exist in egg shape even among strong fliers. Although the reason for each species is likely more complex, this study offers another clue into the evolution of egg shapes in birds. I wonder if anyone has done a similar study of eggs from reptiles…


MC Stoddard, EH Yong, D Akkaynak, C Sheard, JA Tobias, L Mahadevan. Avian egg shape: Form, function, and evolution. Science.  23 Jun 2017: Vol. 356, Issue 6344, pp. 1249-1254. DOI: 10.1126/science.aaj1945

Categories: Reproduction and Development

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