Q On March 24, you had a picture of a painted bunting. What makes such a variety of colors on one bird?
A Feather colors in birds are created two ways, through either unique pigmentation or feather structure, according to Carolyn Byers, director of education at the Madison Audubon Society.
Three pigments contribute to the colorful feathers found on birds: melanin, carotenoids and porphyrins.
Melanin, the same pigment that creates human hair and skin color, displays as black, brown, red and pale yellow in bird feathers, Byers said. Melanin also makes feathers strong, with deeper hues, such as black or brown, correlating with greater feather strength, while lighter colors, like yellow or white, correlate with weaker strength.
While melanin is naturally occurring in birds, carotenoids are produced by plants. Birds display the unique reds, oranges and yellows attributed to carotenoids when they eat specific plants or insects, like spiders or grasshoppers, which eat the carotenoids the birds need for their feather colors.
Porphyrins, which produce pink, brown, red and contribute to green pigmentation, are actually modified amino acids, Byers said. This last pigment has a bright red fluorescence under ultraviolet light.
Besides pigmentation, the second factor behind coloring is structural differences between feathers. Most blue found in birds can be attributed to feather structure. When light passes through certain proteins and pockets of air trapped between feather barbules — tiny filaments extending from the barbs of a feather — it refracts, just like light passing through a prism. Byers said the process produces different hues, such as blue, and an iridescence seen in other feathers, like in the throat patch of a ruby-throated hummingbird.