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Why Are Some Bird Eggs Blue?

Bird eggs can range in color from white to mottled to dark greenish-blue. Scientists have suggested that eggshell pigmentation has something to do either with camouflage, especially for birds that nest on the ground, or protection from the effects of sunlight, especially in nests found in brightly-lit places. To clarify the interactions between eggshell color and sunlight, researchers David Lahti and Dan Ardia studied village weaverbirds, a species that produces a variety of egg colors, and found that nesting environment has a lot to do with the color of a bird’s eggs.

Blue for a reason:

  • If eggs are too dark, they will absorb more light and overheat in sunlight. However, if they are too pale, the researchers found, they will not effectively shield against ultraviolet radiation.
  • The researchers determined that pale blue eggs, most commonly associated with robins, may be the ideal color for protecting a developing embryo from both excess heat and UV radiation, especially in more sheltered settings.
  • For nests in brighter environments, such as open land and more arid regions, the danger of overheating favors white or light-colored eggshells.
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