Eye Color and Development
photographs a Brewer's Blackbird (top) and Sharp-shinned Hawk (bottom) by Rohan Kamath
color of a bird's eye (usually the color of the iris)
results from both pigments and phenomena such as the
diffraction of light. Avian eye colors range from dark brown
and yellow through red, blue, and green to metallic silver
and gold. In some species, eye color differs between the
sexes, as in bright yellow-eyed male and brown-eyed female
Brewer's Blackbirds. The nearly identical sexes of the
European Starling can be differentiated by the presence of a
yellow ring along the edge of the iris in
In many species, eye color changes as the bird matures and can serve as a means of determining an individual's age. Although the physiology of iris pigmentation is poorly understood, changes in color with age and with season are likely to be under hormonal control, especially where colors are closely associated with the sexual cycle. Changes of eye color with age are found in a wide variety of avian families including the loons, grebes, ducks, hawks, pheasants, gulls, alcids, woodpeckers, mimic thrushes, vireos, and blackbirds. Species requiring more than a year to pass from juvenile to adult plumage (such as the Bald Eagle and Herring Gull) generally show a concurrent change in eye color. Some specific examples of age-related changes are Lesser Scaup and Northern Harrier (from brown to yellow), Sharp-shinned Hawk (bright yellow to red), Red-tailed Hawk (yellow to red-brown), American Crow (blue or blue-gray to brown), Dark-eyed junco (gray or gray-brown to red-brown), and Common Grackle (brown, turning paler with age). The evolutionary significance of these
|changes is not clear, but in some birds they may serve to help determine the maturity of potential mates.|
The Color of Birds;
How Long Can Birds Live?
Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.