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anatomy & physiology

Mongabay.com

Rhett A. Butler - San Francisco, CA.

1999-2008.

(below)

           When you look at pictures of frogs do you notice any ears? How do you think they hear the calls of other frogs or predators? The cool thing about frogs is they can hear, they can pinpoint sound locations, and their eardrums, a.k.a. tympanum, and the whole ear structure is “waterproof”. What I mean is they don’t have the ear holes like we do. Their ear starts with a ring of cartilage right behind each eye. That cartilage is covered over by membrane just like with drums. On the outside of the body, the location of the tympanum is behind each eye on the side of the head. In many species if you look closely you may notice this circular mark that is different from the rest of the skin. That’s the tympanum. You may even see a fold of skin above and around the tympanum that resembles an earlobe.

            Anyways, connected to the membrane is a rod-like structure or set of bones that, when vibrated by sound waves, shake the inner fluid, disturbing tiny hairs that move their cells. In turn these hair cells neighbor a group of nerve fibers. The nerve fibers getting rubbed are like, "Hey what is going on here?" and so they, of course keeping up with this game of telephone (but a very accurate version, they don’t mix up the original message), are firing off these electrical impulses to the brain saying, "Hey, I’ve got something to tell you." So the brain listens and deciphers the code. This happens so quickly the frog has time to know what the sound means and react as necessary.

            Another way of hearing, and this is important, is by determining where the sound originated, through using the air caught between the lungs and tympanum. This air way has other purposes as well, like muffling out the strength of many other frog calls together, or possibly picking up on barometric pressure changes.

            Why is there a possibility of detecting barometric pressure changes? Well it’s known frogs call around times of rain when there are pressure and humidity changes. For some, temperature can influence calls. Other frog calls include territorial calls, mating calls, warning calls. And, all these calls come in many different forms, because each frog species has its own dialect and even different accents within different populations of a species. Frogs hear like we do except for our highest highs and our lowest lows. Females pick out calls of their own species from a chorus of other frogs. How do frogs know what they’re listening for? They’re tuned in. They associate frog’s calls with their meanings, but they are “deaf”, in a sense, when it comes to associating other sounds to anything else. They do however listen for nearby predators too.

            The larynx and vocal cords work together with the lungs and closed mouth, which see-saw air between them, to make calls. The only time the mouth stays open during calling is for the alarm calls. There are also the vocal sacs, 1 or 2 which are located in the region of the chin, and the tympana which are thought to help amplify the sound.

Works Cited:

Behler, J. L., & Behler, D. A. (2005). Frogs: A chorus of colors. New York, NY: Sterling Publishing Co., Inc.

Beltz, E. (2005). Frogs: inside their remarkable world. Buffalo, NY: Firefly Books Ltd.

Forsyth, A. (2008). Nature of the rainforest: Costa Rica and beyond. Ithaca, New York: Cornell University Press.

Notice the circular dark spot right behind the eye of this frog (above). That spot is the tympanum, a.k.a. the eardrum, and most frogs have two, one behind each ear. The hyla tree frog (below) also has a tympanum behind each eye, but they are harder to see because of how well they blend into the skin.

Mongabay.com

Rhett A. Butler - San Francisco, CA.

1999-2008.

***On the top of this webpage you will notice a little box on the upper left hand corner. That is the frog eggs (2) photo taken by Erin Milligan in the spring of 2009. The purpose of the picture there is only so I could get a sound clip I recorded to play on the webpage, when opened. The sound clip was made on April 27, 2009 & it is frog calls, spring peepers breeding call I believe but I'm not positive (so do not hold me to that please). It is definitely frog calls though. It was recorded with my computer so it's not loud and you'll probably have to turn the volume all the way up to hear it properly. Sorry about the background noise, like I said I used my computer to record. Enjoy :)***