Bird of a different color? Blame the humidity

Tree swallows’ iridescent feathers change from blue-green to muted yellow when exposed to humidity. The plumage reverses to previous color tones as humidity decreases.

This discovery by Chad Eliason, a University of Akron integrated bioscience Ph.D. program student, and Dr. Matthew Shawkey, assistant professor of biology and integrated bioscience, is published in the Sept. 27 issue of Optics Express, the international journal of optics.
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Rapid, reversible response of iridescent feather color to ambient humidity