Birds go through a series of "mini-molts" as they grow from fuzzy chicks to fully feathered birds -and that is what appears to be going on with the bird shown. That said, a close inspection will help you to determine whether there are any mites or lice present.
Young chickens go through several feather changes on their way to adult plumage. New feathers come in covered in a waxy shaft. This looks white. It breaks down as the feather emerges.
This thread shows a good picture in the second post and explains it.