The uropygial gland secretes an oil (preen oil) through the dorsal surface of the skin via a grease nipple-like nub or papilla. The oil contains a complex and variable mixture of substances formed greatly of aliphatic monoester waxes, formed of fatty acids and monohydroxy wax-alcohols.
The uropygial gland generates an oily substance (preen oil) from the dorsal skin surface through a grease nipple-like structure. This substance is rich in a complex mixture of substances primarily consisting of aliphatic monoester waxes, which are made up of fatty acids and monohydroxy wax-alcohols.