That classic image of a frog with a bulging throat passing air across his vocal chords is not the only way by which frogs inflate themselves. Frogs are capable of puffing up other parts of their bodies for various reasons. In some cases, frogs inflate their trunk and belly by diverting air to those sections of their bodies, making them swell in an effort to get rid of unwanted attention.
Inflating, or making themselves look bigger, can be a defense mechanism used by frogs. When threatened by a predator that likely could end their existence, frogs often inflate in an attempt to appear too big to eat. The Exploratorium explains that the tomato frog of Madagascar puffs itself up like a balloon to convince predators that he is too large to swallow.
To Avoid Sex
It turns out girl amphibians will use size to their advantage when they aren't open to the sexual advances of a potential male suitor. Frog sex is called amplexus, and is achieved by the male mounting the female from the back and grasping her with his front legs. They remain in this position while she lays eggs and he fertilizes them. If she isn't "into him," she can inflate her body, making it difficult for him to stay in place and easier for other male frogs to push him off her.
To Get Sex
In most frog species, it is the male sending out the call to mate. He inflates his vocal sacs on his throat, providing an effective chamber to amplify the sound of air rushing across his vocal chords. Each species has its own specific call -- it's Mother Nature's way of keeping male and female frogs attracted to and mating with their own kind. Yet, with every rule there is an exception. For the South African clawed frog, it is the female that inflates the vocal sacs, advertising her desire.
To Communicate With Each Other
Not all sounds made by frogs inflating vocal sacs are solely sirens for sex. Frogs, male and female, use the inflation of their vocal sacs for a variety of communicative purposes. The various chirps, trills, twitters and croaks heard at ponds, particularly in the night-time hours, are a language of predator warnings and location indicators that only the frogs can interpret.
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