![]() The word iridescence comes from the Latin and Greek iris, meaning rainbow. Iridescence, by contrast, is a form of structural coloration. Other pigments called melanin are naturally occurring in the skin and feathers of birds (much like melanin in human skin and hair), producing a range of black, grey, brown, and orange colors. Pigmentation is “the natural coloring of animal or plant tissue.” Some birds acquire pigments called carotenoids through their diet, like flamingos who develop their pink coloring from eating shrimp. The color we observe in bird feathers is derived from the pigmentation of the feather, the structure of the feather itself, or a combination of the two. ![]() While observing a pair of pesky starlings at my bird feeder one day, the gleam of their feathers caught my eye and caused me to wonder: Why do some birds have iridescent feathers while others do not? What causes iridescence, and how does it serve the birds who flaunt these feathers? What do tree swallows, starlings, pigeons, hummingbirds, and mallard ducks all have in common? Besides being birds, of course, each of these species sports iridescent feathers that glimmer and shine when the light hits them. Photo by Keith Williams, CC BY-NC-ND 2.0. Feathers’ iridescence depends on refracting light, sometimes gleaming more vibrantly, as in this photo of a tree swallow.
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