Frogs don't have external ears, but they do have ear holes, located directly behind their eyes. Frog ear holes are covered with thin tympanic membranes, or eardrums, that protect the inner ear cavity and help transmit sound vibrations. Male frogs' eardrums are larger than their eyes; females' are smaller. Good hearing is essential for frogs' survival. They listen for distress signals, mating calls and territorial warnings.
Frog Eardrums Vibrate
Having no external ears doesn't compromise a frog's hearing. A rod connecting the frog's eardrum to his inner ear wiggles when sound wave vibrations occur. Fluid in the inner ear splashes, causing tiny hairs to wave and make contact with nerve fibers. This contact generates electrical impulses that convey to the brain, which reads the electrical signals as sounds.
Their Lungs Lower Amplification
A continuous air link occurs from frogs' lungs to their eardrums. On the side that sound is coming from, the lungs place pressure on the eardrum. This may help locate the sound's origination point, allowing females to locate their mates and helping males to identify territorial boundaries. Their lungs also equalize pressure between the external and inner eardrum surfaces, lowering the amplification of the frogs' own voices, enabling them to croak loudly without hurting their ears.
A Species That Hears Via Lungs
Panamanian golden frogs have no external or middle ears but are able to hear and locate sounds with their inner ears. Their lungs are located close to the skin and function as eardrums. These frogs' lungs pick up sound wave vibrations are and convey them to the inner ears, which function as other species' do and send impulses to their brains for interpretation.
One Hears Via Mouth
Gardiner's Seychelle frogs, one of the world's tiniest frogs, resonate sounds through their cavernous mouths, instead of eardrums. They also have no external or middle ears, and have functional inner ears. X-ray imaging has revealed that small bones conduct sound wave vibrations from Gardiner's frogs' mouths to their inner ears.
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