If you have ever been outside on a warm night you know just how loud Frogs and Toads can be. Frogs and Toads call to attract mates. Male Frogs and Toads call to attract females. Below is a video of an American Toad Calling to attract a mate. I took this video in a pond behind my house using a Canon 100mm macro lens and Canon Rebel T4i.
You can see in the video the Toads eardrum is the circular indention behind their eyes. You can also tell from the video that this toad calls quite loud, Frogs and Toads are able to call at upwards of 90 decibels. Frogs and Toads have quite sensitive hearing, it begs the question how do they not damage their eardrums and deafen themselves with their loud calls. Scientist have discovered that Frogs hear with both their ear drums and their lungs and a pressure system builds inside the Frog that minimizes vibrations from internal noises made by the frog. To further elaborate on this I need to talk about how a frogs ear drum works. A frogs ear drum is called a Tympanum. A frogs Tympanum works in ver much the same way that our human ear drums work. A frogs ear drum, just like a humans ear drum is a membrane that is stretched across a ring of cartilage like a snare drum that vibrates. There is rod that is connected to the ear drum , which vibrates by sounds that come at the frog.Remember from school that sound is just pressure waves. The rod sloshes around in the inner ear fluid, which causes microscopic hairs to move, which send signals to the frogs brain for interception. A frogs ear lungs also vibrate when sound waves come toward the frog, although they are less sensitive than the frogs ear drum. Some frogs like the Spring Peeper, pictured right
Spring Peeper on a Twig Copyright 2013 Last Mile Photography
have a call that are so loud that they heard for up to one mile away. These creatures are so noisy that it is a wonder that they do not hurt their ears and deafen themselves with their own calls. Frogs have a very clever method of making sure that their own loud calls do not hurt their own hearing. In 1988 Scientist Peter Narins who is a professor at UCLA of Physiological science found have found that frogs have an internal pressure system, a closed air loop. that keeps the frogs own ear drum from vibrating excessively from its own call. Scientist have found that pressure builds between their lungs and ear drum, which then equalizes the pressure between the inner and outer surfaces of the frogs ear drum, which greatly cuts down on the vibrations that a frog experiences, from their internal calls. It is also believed that another purpose of the closed loop pressure system is so the Frogs can detect the direction a sound is coming from with its lungs so frogs can escape danger while calling. Being in the vicinity of frogs calling can subject a human to sounds so loud that they are upwards of 90 db ,which can cause discomfort and hearing loss for humans.
Sources: Holladay APril: Frogs Can Hear Without Ears. 4/26/2001. http://usatoday30.usatoday.com/news/science/wonderquest/2001-04-25-frog-ears.htm