Distribution Amongst Species
The gland is invariably present at embryonic stages, whereas it can be vestigial in adults of certain orders, families, genera and species. Some or all species in at least nine families of birds lack a uropygial gland. These include kiwis (Apterygidae), emu (Dromaiidae), ostriches (Struthionidae), rheas (Rheidae), cassowaries (Casuariidae), mesites (Mesitornithidae), bustards (Otididae), pigeons and doves (Columbidae), Amazon parrots (Psittacidae), frogmouths (Podargidae), and woodpeckers (Picidae). These birds typically find other means to stay clean and dry, such as taking a dust bath. See also powder down. Researchers have been unable to correlate the presence or absence of the uropygial gland with factors such as distribution, climate, ecology, or flightlessness.
Read more about this topic: Uropygial Gland
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