The nose of the male proboscis monkey amplifies its threatening call by serving as a resonating chamber.
"A large mobile nose, like that of the elephant, may also be known as a proboscis: hence the name of the proboscis monkey, a curious-looking primate, the male of which has a long bulbous nose that hangs over his mouth. This kind of nose is used as a resonating chamber, and is erected to amplify the male's threatening call through the forest canopy of Borneo." (Foy and Oxford Scientific Films 1982:136)
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