chicken and quail eggs chicken and quail eggs Different bird species lay very different types of eggs. Scientists never knew why – until now. (Photo: CKP1001 / Shutterstock)

We finally know why eggs are so different in shapes and sizes

Scientists make a surprising discovering while studying hundreds of bird species.

How do you like your eggs? Scrambled, sunny side up, hard-boiled, over easy?

If you're one of the distinguished scientists studying the diversity in shapes and sizes of eggs, your answer might be somewhere in the area of "pointy, oblong, asymmetrical, coneheaded."

Those scientists – who hail from the U.K., the U.S., Israel and Singapore – have hatched some pretty revealing conclusions from studying more than 1,400 species of birds to determine how their eggs developed their unique shapes and sizes. For example, why are the eggs of brown hawk owls almost perfectly spherical, while those of the common murre and sandpiper are shaped more like teardrops?

circa 1830: The eggs of the songthrush, Gold-crest, Swallow, Wren, Jay, and Kingfisher. A circa-1830 illustration of the eggs of the songthrush, gold-crest, swallow, wren, jay and kingfisher. (Photo: Hulton Archive/Getty Images)

Those observations in shape are nothing new. But why they are shaped this way – and how they got there – has been unanswered for years.

Finally, however, the answer revealed itself. And it's all about how the birds fly.

"We discovered that flight may influence egg shape," said lead author Mary Caswell Stoddard, an assistant professor of ecology and evolutionary biology at Princeton University. "To maintain sleek and streamlined bodies for flight, birds appear to lay eggs that are more asymmetric or elliptical."

The research, published recently in the journal Science, found that certain species have evolved to make it easier for the birds to fly. This explains why chicken eggs are bigger and bulkier; the species is not exactly known for its stellar flying ability.

Hummingbird and albatross eggs, however, are smaller and more aerodynamic. The team was assisted by nature photographer Derya Akkaynak, who is a postdoctoral researcher at Israel's University of Haifa.

Anna's Hummingbird in flight with purple flowerAnna's Hummingbird in a blink-and-you'll-miss-it feeding frenzy. (Photo: Keneva Photography/Shutterstock)

Other factors, like calcium in the diet, have led to differences in shape as well. But the biggest surprise, researchers said, was how closely linked egg shape was to flight ability.

"With these egg shapes, birds can maximize egg volume without increasing the egg's width – this is an advantage in narrow oviducts," Caswell said.

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