Birds replace their feathers by molting, the periodic shedding of old feathers and the growing of new ones. They do this one to three times each year, although different birds molt at different times of the year. Male goldfinches, for example, molt from a dull greenish yellow to bright yellow during spring. The periodic shedding of feathers and their replacement with new ones makes perfect sense in the animal kingdom.
Feathers are incapable of further growth, and may get worn down, broken, and faded over the year from normal wear-and-tear. Molting replaces these damaged feathers and helps the males look attractive to females, which is why many molts take place during the mating season.