Feather Differentiation of plumage
The first juvenile plumage of birds is usually replaced before the first winter. This winter plumage usually resembles that of an adult female irrespective of whether the juvenile is male or female. Only in the second year does differentiation of plumage between males and females occur. Mature male and female plumages frequently differ in colour (sexual chromaticdimorphism), especially during the breeding season, when the male may be particularly brightly coloured (eg Red Bishop birds Euplectes orix). Such colour changes are used during courtship with male birds advertising themselves. Breeding plumage may facilitate mate recognization within a species, and is particularly important when many related species coexist in the same area. In particular striking combinations of colour are used in finches (Fringillidae) and parakeets/ parrots. Worldwide ducks assemble in multispecies flocks, but during breeding each drake (male) species will acquire a unique colour and pattern combination particularly in the head regions which will distinguish that species from other duckspecies in his quest to find a mate. Colour may also be used to effectively camouflage birds. The most striking being the ptarmigan (Lagopus mutus; Tetraonidae), this grouse is white during winter when snow is on the ground, but mottled brown during the rest of the year.