Sounds are produced by at least 47 species of turtles, even though they lack vocal cords and they do not vocalize often. Chelonians (turtles, tortoises and terrapins) can make sounds by swallowing or by forcibly expelling air from their lungs.
Turtles may vocalize when mating or seeking a mate, when they are sick or in distress or for other reasons. The redfooted tortoise makes a clucking sound, while the giant musk turtle yelps when it is attacked or frightened. Nesting female leatherback sea turtles make a belching sound, and male Travancore tortoises use a high-pitched whine to attract mates. Sounds have even been detected from unhatched baby leatherback sea turtles. It is believed these sounds help to coordinate hatching.