I found this tidbit from the Cornell Lab of Ornithology:
A feather is a "dead" structure, somewhat analogous to hair or nails in humans. The hardness of a feather is caused by the formation of the protein keratin. Since feathers cannot heal themselves when damaged, they have to be completely replaced. The replacement of all or part of the feathers is called a molt. Molts produce feathers that match the age and sex of the bird, and sometimes the season.
Molting occurs in response to a mixture of hormonal changes brought about by seasonal changes.
In case you don't believe me, here are some "before and after" photos to illustrate just how unattractive the ladies are right now.