If a bird’s feathers get too dried out, they become brittle. To prevent that from happening, most birds have a gland located above the base of the tail that produces oil. They use their beaks to massage oil from the gland into their feathers to keep them supple. A bird first grips a feather in its beak near the feather’s base. Then it slides its beak along the length of the feather toward the tip. This action smoothes together the tiny structures—called barbules—that make up the feather, while also removing dirt and small parasites.
