This story is brought to you by BirdNote, a show that airs daily on public radio stations nationwide.
Peer into the world of birds, and eyes of many different colors peer back.
There are shades of light and dark—yellows, whites, greens, the red eyes of certain hawks, ducks, loons, herons, and songbirds. These colors really pop because birds have no white around the iris like we do. So the yellow eyes of a Great Horned Owl or a Herring Gull seem to give the birds a fierce, penetrating glare. If you picture them with soft brown eyes, though, suddenly they seem much less intimidating.
While eye color isn’t tied to one group of birds or another, a pattern common to many birds is a change in eye color as immature birds grow to adulthood. Bald Eagles, Ring-billed Gulls, and ducks such as goldeneyes and scaup have brown eyes as youngsters, and yellow as adults. Red-tailed Hawks reverse this pattern, with their eyes changing from yellow to brown, while the yellow eyes of a young Cooper's Hawk turn deep red as it reaches maturity.
Not all birds’ eyes change color as the birds age. But for those whose eye color appears to signal adulthood, this is likely an adaptation that helps them gauge the maturity—and suitability—of potential mates.
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Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Great Horned Owl  recorded by William R Fish. Ring-billed Gull  recorded by L R Macaulay. Cooper’s hawk  recorded by Gerrit Vyn.
Surf ambient—NatureSound # 23 Surf Moderate Sandy recorded by Gordon Hempton of https://quietplanet.com/.
BirdNote’s theme music was composed and played by Nancy Rumbel and John Kessler.
Producer: John Kessler
Executive Producer: Dominic Black
Written by Bob Sundstrom
© 2016 Tune In to Nature.org April 2016 Narrator: Mary McCann