When a bird grooms himself, he distributes oil from the uropygial gland, or preen gland, over his feathers to maintain their insulation and waterproofing properties. This act of self-grooming is called preening. Most avian species have a preen gland, but a handful of species do not. Birds lacking this special anatomical feature don’t spend a great amount of time in water or bathing, and don’t need a preen gland.
Birds Lacking a Preen Gland
Two species of large birds that lack an uropygial gland are the emu and ostrich. Neither bird spends a great deal of time near or in water and both are more apt to take a dust bath to stay clean. The dust bath also helps them to stay parasite-free. The anatomy of woodpeckers does not include a preen gland. Other commonly known birds lacking this gland are doves, pigeons, rheas, and kiwis. Cassowaries, bustards, frogmouths, and mesites are among bird families that include many species without a preen gland.
What Does the Preen Gland Do?
The oil-like substance from the preen gland contains an inactive form of vitamin D. When the bird preens, he spreads the oil over the feathers. Sunlight activates the vitamin, which plays an important role in preventing breakage and drying of the feathers. Geese, ducks and pelicans have very pronounced preen glands. Waterfowl species depend greatly on the oil from the gland to waterproof their plumage.
More Benefits of the Preen Gland
Antimicrobial and antibacterial properties are another benefit of the preening oil. Parasites and lice are less likely to be bothersome to a bird with a well-functioning preen gland. The preen gland oil in some bird species contains a pheromone that helps the bird attract a mate. The preening oil of some bird species has a foul odor that keeps parasites away and assists in keeping predators away from nesting birds and their young.
Where is the Preen Gland?
It is easiest to see the preen gland just above the base of the tail in hatchlings or chicks who are not yet fully feathered. Once the feathers are in, they conceal the gland. The gland may vary in size and shape according to the bird's size and species, but it usually looks like a nipple or teat. Most people have watched birds preening while perched on the branch of a tree or settling in before dusk. With thousands of feathers that must be kept in pristine condition for warmth and flight, birds spend a great deal of time using the oil produced by their preen glands.