Sound bladder
Sound bladders are bag-like, differently voluminous protuberances of the floor of the mouth in the males of many frogs (anura). In the mating season they serve as a resonance space to reinforce the mating calls ("croaking") in order to attract females.
The elastic wall of the sound bladder consists of an inner layer of mucous membrane , a body skin that is more or less wrinkled in the resting position and, in between, a bulging of the floor muscle of the mouth subhyoid . In a quasi-closed system of sound bladder, larynx and lungs , the sound is generated when the air flows through the larynx, causing the vocal cords to vibrate. The sound bubble increases the volume and thus the acoustic range of the sound waves generated by the call .
Mostly it is a single subgular (throaty) sound bladder, which the animal can inflate very voluminously. European examples are European tree frog , natterjack and green toad . In some American tree frogs, subgular vocal sacs appear with a hint of two-part (bilobatic) to paired characteristics. Male water frogs have paired, lateral (lateral) vocal sacs, that is, they have a vocal sac under each corner of the mouth, which is turned inside when not in use.
Some anurans lacks a vocal sac, others only have internal vocal sacs, so their calls are much quieter, such as in common toad and frog . As a rule, these are so-called “traditional spawners” ( k-strategists ) who always return to the same spawning water in the same location , so that finding a partner over greater distances by means of acoustic signals plays less of a role. Internal vocal sacs are less distended and, unlike species with an external throat vocal vesicle, are not characterized by skin folds when they are at rest.
literature
- Klaus Kabisch: Dictionary of Herpetology. Gustav Fischer Verlag, Jena 1990, ISBN 3-334-00307-8 , p. 380.
