"Most birds, even predominantly white birds like gulls and pelicans, have drak primary feathers or feather tips. The melanin granules that make feathers black or dark brown are always associated with increased amounts of keratin, which strengthens feathers. Dark areas of feathers thus are stronger and resist abrasion more than lighter or white areas (Página 90 - Manuel of Ornithology. Avian Structure & Function - Noble S. Proctor & Patrick J. Lynch - Yale University 1993)
Inglés - Inglés: (noun) a fibrous protein forming the main structural constituent of hair, feathers, hoofs, claws, horns , etc..
Fuente: Oxford Dictionaries