The stark red of a cowbird’s eyes comes from unusually large blood vessels, whereas the Canvasbacks and vireos depend on two completely different types of pigment compounds. “Canvasback, Red-eyed Vireo, and Bronzed Cowbird are all fairly common North American species with bright red eyes, but the chemical mechanism that creates those red eyes are completely different,” Corbett says. For example, Corbett recalled his surprise upon looking into the factors behind three different red-eyed birds. The answers to these questions aren’t necessarily the same for all birds-or even species with similarly colored orbs. In particular, the team focused on three topics: the pigments and structures birds use to create different eye colors, the genetics underlying those diverse hues, and the evolutionary function this variation may serve. To better understand what we do know about avian eye color, Corbett and his coauthors set out to trawl through a century of research, gathering together the tidbits scientists have discovered over the years into one comprehensive paper.

Where male Wood Ducks sport red eyes, females show dark brown. Brown Pelicans’ brown peepers lighten to blue during the breeding season while herons’ eyes can redden. The eyes of the underappreciated Rock Pigeon fade from orange at the edge to yellow around the pupil, while a juvenile Osprey’s orange eyes turn yellow at maturity.

But in many cases, they also have these really brightly colored or variably colored eyes,” he says.Īnd, like feathers, dramatic eyes can be found in even the most common species. student at Louisiana State University and lead author on the new study. “When we think about bird coloration, we’re almost always thinking about feather coloration: A cardinal is red, a Blue Jay is blue,” says Eamon Corbett, an ornithology Ph.D. And, somewhat surprisingly, scientists know very little about the hows and whys behind all this variety.Ī recent study shines a spotlight on the diversity of avian eye color while calling on scientists to further investigate the incredible array of hues: red, yellow, blue, pink, white. Feathers steal the show, but there’s another feature every bird has that also comes in a rainbow of colors: their eyes.

Coolest eye colors