A resonating device is a structure used by an animal that improves the quality of its vocalizations through amplifying the sound produced via acoustic resonance. The benefit of such an adaptation is that the call's volume increases while lessening the necessary energy expenditure otherwise required to make such a sound. The resulting sound may also radiate more efficiently throughout the environment.
The resonator may take the form of a hollow (a resonant space), a chamber (referred to as a resonating chamber), or an otherwise air-filled cavity (such as an air sac) which may be part of, or adjacent to, the animal's sound-producing organ, or it may be a structure entirely outside of the animal's body (part of the environment). Such structures use a similar principle to wind instruments, in that both utilize a resonator to amplify the soundwave that will ultimately be uttered.
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