What Causes Iridescence In Feathers?


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Patricia Devereux Profile
There are two kinds of colors in birds' plumage: those caused by pigment, and those by feather structure. Iridescence falls under the latter category. What we perceive as the brilliant flash of a ruby-throated hummingbird's gorget (throat) are actually black feathers.
Feather structure colors may be caused by refraction of light or interference, which produces the colors in thin films such as soap bubbles.

The tips of iridescent feathers have barbules with minute, coloured platelets. Therein are air bubbles, and the thickness of the platelet and amount of air in it determines the color seen.

Light hitting platelets horizontally reflects as colour; vertical light is absorbed and results in the absence of colour: black.

The barbules of birds' gorgets and crowns are like mirrors, and light hitting them can be reflected in just one direction. Birds use this property by positioning themselves in sun so as to "flash" potential mates and rivals.

Barbules on a bird's back resemble concave mirrors, so light is reflected from all directions.

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