In Berlin Steglitz (Germany)…
The colors of feathers are produced by the presence of pigments such as melanins (browns, blacks, greys), carotenoids (reds, yellows, orange), psittacofulvins (unique red pigments found in some parrots) and porphyrins (such as the green turacoverdin of Turacos) or more often by feather structure. Structural coloration is involved in the production of most greens, blues, iridescent colors, ultraviolet reflectance and in the enhancement of pigmentary colors.
In some birds, the feather colors may be created or altered by uropygial gland secretions. The yellow bill colors of many hornbills are produced by preen gland secretions. Other differences that may only be visible in the ultraviolet region have been suggested but studies have failed to find evidence. Uropygial oil secretion may also have an inhibitory effect on feather bacteria.
A bird’s feathers undergo wear and tear and are replaced periodically during its life through molting. New feathers are formed through the same follicle from which the old ones were fledged. The presence of melanin in feathers increases their resistance to abrasion. Melanin based feathers were however found to be faster degraded by bacteria than those with carotenoid pigments. This has led to the suggestion that Gloger’s rule, the observation that birds from more humid regions tend to be darker may be related to the increased bacterial load and the selection for greater melanin. The evolution of coloration is based on sexual selection and it has been suggested that carotenoid based pigments may have evolved since they are likely to be more honest signals of fitness since they are derived from special diets.
In India, feathers of the Indian Peacock have been used in traditional medicine for snakebite, infertility and coughs.