Bird eggs laid in cold climates are darker, which may keep eggs warm

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Bird eggs come in a dizzying array of colors. But from a global perspective, that diversity follows a simple pattern — the colder the climate, the darker the egg, new research shows.

Darker eggs absorb more heat than lighter ones, which could help developing chicks stay warm while their parents forage for food, according to the study published online October 28 in Nature Ecology and Evolution.

Biologists have long tried to suss out the selective forces that shape and color a specific species’ eggs. Those forces include keeping eggs hidden from predators, protecting them from bacteria, signaling egg quality and maintaining egg warmth. “All of these hypotheses have some level of [evidential] support,” says Phillip Wisocki, who worked on the research while studying biology at Long Island University Post in Brookville, New York.

But scientists weren’t sure whether any of these factors were important in determining egg diversity globally. “If your focus is too narrow, you can miss a lot of what’s going on,” says Wisocki’s adviser, biologist Daniel Hanley.

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