Uropygial gland

The preen gland (Latin: glandula uropygialis ) is the only skin gland of many species of birds. It is located on the top of the tail, the rump. In the two-lobed, holocrine gland an oily secretion is formed, which distributes the bird with the beak or with the legs in the entire plumage. This regular greasing is an essential part of the plumage hygiene that preserves the softness of the plumage and it's water resistant due to the better integration thereby ensured. In addition, the secretion contains also fungicidal and bactericidal ingredients. Perhaps the Bürzeldrüsensekret also plays a role in vitamin balance by containing vitamin D precursors. The primary lipid component is a diester wax.

Especially designed the preen gland is in most swimming birds. In some birds, such as the hoopoe, the preen gland is fully functional only in early stages of development of the young birds; the excreted by their secretion is extremely malodorous and is also used to ward off predators.

Some birds such as the emu, cassowary, the Great Bustard and many parrots and pigeons species have in adulthood has no functional preen gland. Often in representatives of these genera the plumage hygienic function of the preen gland is replaced by so-called Puderdunen.

Karotinoidhaltige Bürzeldrüsensekrete, which are applied as a cosmetic paint on the plumage, is found in eight species of Asian hornbills and two pelican species. The pink plumage of gulls and terns during the breeding season due to a storage of Astaxanthinpigmenten and not, as previously assumed by an application of Bürzeldrüsensekreten.