|a gland, situated at the base of the tail in most birds, that secretes oil used in preening|
in birds, an organ located on the back near the base of the tail. Paired or in two united halves, it is found in most birds. Absent in ostrich, emu, cassowary, bustard, frogmouth, and a few other birds, the oil gland is best-developed in aquatic species, notably petrels and pelicans, and in the osprey and oilbird.
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