The feathers are keratinized as is the beak. The legs have thick scales. The uropygial gland is used to produce oil to preen the feathers. The typical feather is a contour feather. It functions in flight.
Barbs project from the shaft.
Barbules extend out from the barb and hook together to keep the feathers in good shape. Birds will use their bills to help keep the barbules in place. Mammals have a thick dermis layer. Reptile scales come from the epidermis, but the dermis is involved in their production. The epidermis in the place where the scale will form becomes raised and dermis comes up into the raised area.