How can a bird replace worn feathers and still keep moving?

A feather can flex and its barbs can be smoothed back together, but a fully grown feather cannot heal a broken shaft. Its exposed structure is no longer living tissue. Replacing worn feathers requires growing new ones from follicles in the skin.

During molt, old feathers are shed and replacements develop. Many flying birds replace their major flight feathers in a sequence rather than dropping them all together. New feathers grow while enough of the wing remains to support movement.

This is not a universal schedule. Ducks and some other waterbirds can lose many flight feathers together and become temporarily unable to fly. Their molt fits a different way of living and using habitat.

Building feathers needs nutrients and energy. Molt timing often avoids other demanding periods such as migration or raising young, though real schedules vary with species, age and conditions. A change of plumage can also alter appearance, but a bird does not choose each new color as it grows.

The bird’s covering is a maintained structure, not a coat that lasts forever. Life keeps working partly by renewing parts at times that fit the rest of the system.