Vocal sac

A flexible, expandable pouch in many frogs that amplifies or modifies sound during calling. It acts as a resonator, helping shape calls and often making them louder.

Larynx: A structure in the throat that produces sound through vibrating tissues as air passes through it. The larynx generates the call that the vocal sac then resonates or modifies.
Anuran: A member of the amphibian order Anura, which includes frogs and toads. Vocal sacs are characteristic structures in many, but not all, anurans.
Mating call: A signal produced by an animal to attract or court potential mates. Many frog vocal sacs enhance calls used by males to attract females.
Vocal sacless frog: A frog species that produces calls without an external vocal sac. Its calling shows that frogs can vocalize without the pouch’s acoustic and visual effects.
Vocal sac inflation: The expansion of a frog’s vocal sac as air enters it during calling. Inflation couples the pouch to the airflow and sound of a call.
Amphibian skin: The thin, permeable skin of amphibians, which supports water and gas exchange. The sac is a specialized extension of the throat region, distinct from ordinary skin function.
Territorial call: A signal used by an animal to defend or advertise occupancy of a territory. Some frogs use sac-assisted calls in interactions with rival males.
Bird syrinx: The sound-producing organ in birds, located where the trachea divides into the bronchi. Unlike the frog sac, the syrinx generates sound directly through specialized vibrating tissues.
Acoustic resonance: The amplification of sound at frequencies matching a system’s natural vibration modes. The sac’s resonant properties alter the frequencies and intensity of frog calls.
Vocal fold: A fold of tissue that vibrates in airflow to generate sound in many vertebrates. Frog sound production uses laryngeal tissues rather than the mammalian vocal-fold arrangement.

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