Above : Pileated woodpecker . Below : Belted kingfisher . Above : Blue jay . Below : Painted bunting , female .
Photo by John Chapel
Photo by Robert Hill
Photo by Robert Hill
Photo by Robert Hill
The other ingredient that determines bird coloration is the structural properties of feathers or skin . Feathers are highly intricate objects made up of a central shaft , called a rachis , and a vane , the flat piece that forms the feather ’ s general shape . The vane is composed of thousands of parallel branches called barbs . The barbs are held in place Feather microstructures must reflect and absorb short and long wavelengths of light differently so that only a portion of the daylight that reaches the feather is bounced back to the observer . This scattering of light occurs when materials in the inner layer of keratin on the barbs are the correct size to reflect short wavelengths ( blue and violet ) but too small to reflect longer wavelengths ( green , yellow , orange , red ). The inner melanin layer absorbs the longer wavelengths resulting in only short wavelengths being reflected , producing a blue or violet color . The intensity or hue of the reflected color depends on the size and spacing of the feather microstructures . Non-iridescent coloration combined with yellow carotenoid pigments produces the green and olive colors that we see in female painted buntings and Tennessee warblers .
In contrast to non-iridescent coloration produced by microstructures in the feather barbs , iridescent coloration is created within the barbules . Because the barbules are structurally different than the barbs , light reflects differently . Rather than having a single inner layer of melanin like in the barb , the barbules can contain several melanincontaining keratin layers . Light bouncing off the different layers repeatedly magnifies some colors and cancels out others . The more layers involved in the production of iridescence , the more intense the color display will be . Birds such as the common grackle with only a single layer show a more subdued iridescence than the throat feathers of many hummingbird species , which are made up of multiple layers .
The Function of Color The coloration of birds can serve many purposes . Feathers are essential in the thermoregulation of birds . Not only does the structure of the feather keep birds cool in the summer and warm in the winter , but the color of those feathers also
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