Why do so many birds lay blue eggs?

Bright blue eggs are beautiful, and relatively common among birds. Find out why.

Dunnock bird nest with 5 eggs. © 49pauly/Getty

The question of why so many birds lay bright blue eggs has intrigued David Lahti since childhood – examples include the dunnock, the American robin and the starling.

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“My parents bought me a book about commonly asked questions. One was, ‘Why are American robin eggs blue?’ The answer essentially said, ‘We don’t know.’ My young mind was struck by the fact that there were simple questions to which science had not yet provided answers.”

Lahti is now a City University of New York biologist, who may have solved the mystery at last.

His experiments on village weaverbirds, a species with highly variable egg colours, suggest that blue is a compromise between protecting the developing embryo from the damaging effects of overheating and ultraviolet radiation.

If eggs are too dark, they will overheat in the sun. Too pale, and they do not shield against ultraviolet radiation.

But Lahti’s curiosity is far from satisfied. “Why do emus lay such dark eggs? Why are Japanese bush warbler eggs brick red? And why are tinamou eggs so glossy?” he wonders.

Source The American Naturalist

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