Birds molt because their feathers wear out, as clothes do, and need to be replaced. The process is called “molting.” Birds molt their feathers at least once a year, in late summer or early fall.
Feathers are dead structures at maturity which are gradually abraded and need to be replaced. Feathers are made from a substance called “keratin.” It is basically the same material your hair is made of.
In molting, old worn feathers drop out of their sockets in a bird’s skin and new ones grow in their place. Some birds grow bright, new feathers for the nesting season. These birds molt twice a year. Most birds molt just a few feathers at a time, so they are able to fly during molting periods.
It is generally a slow process as birds rarely shed all their feathers at any one time; the bird must retain sufficient feathers to regulate its body temperature and repel moisture. The number and area of feathers that are shed varies.
In some molting periods, a bird may renew only the feathers on the head and body, shedding the wing and tail feathers during a later molting period. Some species of bird become flightless during an annual “wing molt” and must seek a protected habitat with a reliable food supply during that time.