There are birds such as; types of doves, pigeons, woodpeckers, etc, that have special feathers that they grow to fall apart at or about the ends of their feathers into a type of powder down that they will use to clean and protect their feathers; some birds will use the fine powder as a water-proofing agent
The special feathers, are called powder down,it is the only type of feathers that the birds has that will keep growing all the time doing the bird’s life.
The birds other feathers will not molt ( fall off} all at the same time. The reason being that the birds needs to keep most of their feathers for flying, and keeping warm. The birds will slowly loss and replace their feathers with new ones over a period of several months.
This Mourning Dove is cleaning its feathers.