Topic summary
Preen oil
Extracted from the Wikipedia article Uropygial gland.
Feather and body integrity
Preen oil is believed to help maintain the integrity of feathers. In waterbirds, preen oil maintains the flexibility of feathers and keeps feather barbules from breaking. The interlocking barbules, when in good condition, form a barrier that helps repel water (see below). In some species, preen oil is also believed to maintain the integrity of the horny beak and the scaly skin of the legs and feet. It has also been speculated that in some species, preen oil contains a precursor of vitamin D; this precursor is converted to vitamin D by the action of sunlight and then absorbed through the skin.