The penguin’s specialized skin gland that produces oil for waterproofing its feathers is the uropygial gland.
The uropygial gland, also called the preen gland, is located near the base of a bird’s tail. A penguin spreads the gland’s oily secretion through its plumage while preening. This helps maintain feather condition and contributes to the water-resistant surface needed for swimming in cold seas.
Penguins do not rely on oil alone for insulation. Their dense, overlapping feathers trap air, while a layer of body fat provides additional protection against cold water. Regular preening keeps the feathers aligned and helps preserve that insulating air layer.
The uropygial gland should not be confused with the salt gland. Salt glands are associated with removing excess salt from seawater and are located near the eyes in penguins. The preen gland has a different job: it supports feather maintenance. Some birds have large, active uropygial glands, while the size and chemistry of the gland vary among species.