Photo by Dante Fenolio. Exploratorium frogkeeper Ned McAllister talks about the variety and meaning of frog calls . Frogs are formidable musicians. Visit a pond on a spring night and you'll hear a chorus of croaks, twitters, chirps, and trills. The South African clawed frog indicates her interest in a suitor with loud clicks.
Frogs make their calls with the help of one or two pouches of skin called vocal sacs.
Sound is produced when air rushes over the vocal chords on its way from the lungs into the vocal sacs. The vocal sacs work like echo chambers to amplify the sound. Some frog calls are so loud, they can be heard up to a mile away. With any luck, the females are listening. Frogs' ears, called tympanum, look like two flat circles behind the eyes.