Birds have up to 25,000 feathers, and most birds preen, or clean, waterproof and align their feathers, several times a day. Ruffed grouse, as well as most other birds, possess an uropygial gland, or preen gland, on their rump. (Some types of birds, including owls, pigeons, parrots and hawks, lack an uropygial gland and instead have specialized feathers that disintegrate into powder down, which serves the same purpose as preen oil.) The preen gland produces a waxy substance that helps waterproof feathers and keeps them flexible.
Ruffed grouse reach back and rub their beaks on this gland, and then distribute the wax on their body and wing feathers by stroking them toward the tip. The grouse grasps a feather near the base and draws it through the partly close beak, nibbling as it goes. This distributes the wax and cleans parasites from the feathers. In order to preen its head, the grouse must rub it on other parts of its body. Preening is usually done in a fairly open setting but with a degree of overhead protection, so that the grouse can watch for terrestrial predators, while being protected from hawks and owls.
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