The gland that produces oil used for cleaning and waterproofing a birds feather is called the what?

The gland that produces oil used for cleaning and waterproofing a bird's feathers is called the preen gland or uropygial gland. This gland is located at the base of the tail and secretes an oily substance that the bird spreads over its feathers using its beak. The oil helps to keep the feathers in good condition, protects them from water, and provides insulation.