Crest (feathers)
Cockatoos and their smaller cousins, cockatiels, are part of the Cacatuidae family of parrots found in Australia, the Bismarck Archipelago and the Philippines, and are probably the most recognizable birds to feature crests.  Cockatoos and cockatiels possess crests which may be raised or lowered at will. Their crests are used to communicate with fellow members of their species, or as a form of defense to frighten away other species that approach too closely, making the bird appear larger when the crest is suddenly and unexpectedly raised.