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From Brown to Robin Egg Blue

Temperature may influence the color of birds' eggs, the Guardian reports.

Researchers from the US and Australia examined the global patterns of birds' eggshells by characterizing the brightness and color of the eggs of 634 bird species from across the bird phylogenetic tree. As they report in Nature Ecology & Evolution, the researchers found that the brightness and color of the eggs tracked with with the solar intensity and aridity of the birds' ranges.

"Eggs in these colder places are darker brown and then as you go towards the tropics and even the temperate zone there are just more competing selection pressures, so there is more variation in colors," co-author Daniel Hanley from Long Island University tells the Guardian.

Dark eggs, the researchers further found, warmed up more quickly than lighter colored eggs, which they say could be an advantage in cooler regions.

However, Macquarie University's Simon Griffith tells the Guardian that the study doesn't shed light on why some eggs are speckled or striped and others are solid.