page_title: Feather
section_title: Coloration
hierarchical_section_title: Feather / Structures and characteristics / Coloration
caption_attribution_description: English: Avian feather pigments. Left: turacin, purple Center: turacoverdin, green (with some blue iridescence on the lower end) Right: carotenoids, scarlet (with blackish melanin on the wings) Birds are ZFMK specimens of Tauraco bannermani (ZFMK 68.77, left) and Ramphocelus bresilius (ZFMK Müller56, right).
context_page_description: Feathers are epidermal growths that form distinctive outer covering, or plumage, on dinosaurs, both avian and some non-avian, and possibly other archosauromorphs. They are considered the most complex integumentary structures found in vertebrates and a premier example of a complex evolutionary novelty. They are among the characteristics that distinguish the extant birds from other living groups.
  Although feathers cover most of the bird's bodies, they arise only from certain well-defined tracts on the skin. They aid in flight, thermal insulation, and waterproofing. In addition, coloration helps in communication and protection. Plumology is the name for the science that is associated with the study of feathers.
context_section_description: The colors of feathers are produced by pigments, by microscopic structures that can refract, reflect, or scatter selected wavelengths of light, or by a combination of both.
  Most feather pigments are melanins (brown and beige pheomelanins, black and grey eumelanins) and carotenoids (red, yellow, orange); other pigments occur only in certain taxa – the yellow to red psittacofulvins (found in some parrots) and the red turacin and green turacoverdin (porphyrin pigments found only in turacos).
  Structural coloration is involved in the production of blue colors, iridescence, most ultraviolet reflectance and in the enhancement of pigmentary colors. Structural iridescence has been reported in fossil feathers dating back 40 million years. White feathers lack pigment and scatter light diffusely; albinism in birds is caused by defective pigment production, though structural coloration will not be affected (as can be seen, for example, in blue-and-white budgerigars).
  The blues and bright greens of many parrots are produced by constructive interference of light reflecting from different layers of structures in feathers.  In the case of green plumage, in addition to yellow, the specific feather structure involved is called by some the Dyck texture. Melanin is often involved in the absorption of light; in combination with a yellow pigment, it produces a dull olive-green.
  In some birds, feather colors may be created, or altered, by secretions from the uropygial gland, also called the preen gland. The yellow bill colors of many hornbills are produced by such secretions.  It has been suggested that there are other color differences that may be visible only in the ultraviolet region, but studies have failed to find evidence. The oil secretion from the uropygial gland may also have an inhibitory effect on feather bacteria.
  The reds, orange and yellow colors of many feathers are caused by various carotenoids. Carotenoid-based pigments might be honest signals of fitness because they are derived from special diets and hence might be difficult to obtain, and/or because carotenoids are required for immune function and hence sexual displays come at the expense of health.
  A bird's feathers undergo wear and tear and are replaced periodically during the bird's life through molting. New feathers, known when developing as blood, or pin feathers, depending on the stage of growth, are formed through the same follicles from which the old ones were fledged. The presence of melanin in feathers increases their resistance to abrasion. One study notes that melanin based feathers were observed to degrade more quickly under bacterial action, even compared to unpigmented feathers from the same species, than those unpigmented or with carotenoid pigments. However, another study the same year compared the action of bacteria on pigmentations of two song sparrow species and observed that the darker pigmented feathers were more resistant; the authors cited other research also published in 2004 that stated increased melanin provided greater resistance.  They observed that the greater resistance of the darker birds confirmed Gloger's rule.
  Although sexual selection plays a major role in the development of feathers, in particular the color of the feathers it is not the only conclusion available. New studies are suggesting that the unique feathers of birds is also a large influence on many important aspects of avian behavior, such as the height at which a different species build their nests. Since females are the prime care givers, evolution has helped select females to display duller colored down so that they may blend into the nesting environment. The position of the nest and whether it has a greater chance of being under predation has exerted constraints on female birds' plumage. A species of bird that nests on the ground, rather than the canopy of the trees, will need to have much duller colors in order not to attract attention to the nest. Since the female is the main care giver in some species of birds, evolution has helped select traits that make her feathers dull a
caption: Colors resulting from different feather pigments
  Left: turacin (red) and turacoverdin (green, with some structural blue iridescence at lower end) on the wing of Tauraco bannermani
  Right: carotenoids (red) and melanins (dark) on belly/wings of Ramphocelus bresilius
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