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When Is a Blue Bird Not Blue?

By John Gibbons

Mountain Bluebird

Mountain Bluebird, Cabin Lake Viewing Blinds, Deschutes National Forest, Near Fort Rock, Oregon (Photo by Elaine R. Wilson)

When is a blue bird not blue? The answer to this question is always. There actually is no such thing as a blue bird. To find out why, Smithsonian Insider asked Scott Sillett, a wildlife biologist at the Smithsonian Migratory Bird Center.

“Red and yellow feathers get their color from actual pigments, called carotenoids, that are in the foods birds eat,” Sillett explains. “Blue is different―no bird species can make blue from pigments. The color blue that we see on a bird is created by the way light waves interact with the feathers and their arrangement of protein molecules, called keratin. In other words, blue is a structural color. Different keratin structures reflect light in subtly different ways to produce different shades of what our eyes perceive as the color blue. A blue feather under ultraviolet light might look uniformly gray to human eyes.”


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  • William Nicholls

    Semantics, not science. Blue light is blue light whether the color is integral to the feather or not.

  • OnceAMule

    Well, that’s wonderful. Next time we have the rare pleasure of seeing, say, an Indigo Bunting, I can impress all my friends by saying, “that’s not really blue. It’s just a mirage, created by light waves.”

  • Steaphany Waelder

    Anyone with Parrots would be familiar with structural color. Parrots love getting showers and as the feathers become increasingly wet, the brilliant colors fade to a dull brownish. As the Bird preens and dries, the brilliant colors return. This would not be the care if Parrots were solely pigment colored.

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