Venus Montgomery, age 11, of San Francisco, California, for her question:
How does a frog croak?
About 100 assorted frogs and toads enjoy life in North America. Each species croaks his own special note, though it takes an expert to distinguish them all. Most of us are content to enjoy their songs blended together in their famous croaking choruses. The f roggy glee clubs are scheduled to perform on mild spring evenings, usually in quiet locations around marshy ponds or streams. Their assorted voices may sound like croaks to our ears. But to the frogs and toads they are sweet serenades.
The pretty little spring peeper pipes his high notes very early in the spring. Later, other frogs add different notes. Finally the big fat bullfrog completes the chorus with his deep bass notes that seem to come from way down in his boots. The peeper utters his shrill soprano pe ep four times, then pauses and repeats the same song. Various tenors and baritones swell the chorus and from time to time the bullfrog adds his jug o rum note maybe loud enough to be heard half a mile away.
The notes may be different but all of them are love songs, intended to enchant lady frogs in the vicinity. And all frogs create their serenading music in the same way. Of all things, every frog performs his remarkable vocal activities with his mouth closed. This is absolutely necessary to the operation. We vocalize by sending air over the vocal cords as we breathe out and open our mouths to send forth the sounds. The frog is not speechless with his mouth closed because he pumps the same breath of air back and forth between his lungs and his croaking apparatus.
Croaking calls for serious concentration and maximum effort. The frog squats in a comfortable position and usually rears back on his haunches. He takes a breath, then closes his mouth and nostrils. Normally the air passes down the esophagus tube straight to the lungs. But when he croaks it is side tracked from the esophagus through a chamber called the pharynx. The door to the pharynx is the larynx, where two bands of elastic tissue form the vocal cords. As the air is pumped back and forth, these elastic bands vibrate and add those certain sounds. The vibrating air is forced up into the mouth cavity, then forward to fill the vocal sac. There the froggy note is amplified to croaking proportions.
No doubt you have noticed that the frog has loose skin sagging under his wide chin.
Actually this is his vocal sac. When he croaks, the empty bag inflates like a balloon fit to burst. This resonant chamber amplifies the high, medium or low note that each type of frog creates with the vibrating cords in his voice box. He vigorously pumps a breath of air back and forth to create each series of croaks. Then he pauses to breathe out and fill up again to repeat his serenade.
Frogs hear more or less as we do. The male frog is too busy concentrating to chase after a lady friend, but she knows that his love song is meant to guide her to where he waits, doing his very best to attract her attention. And if she happens to be ready to deposit her eggs, she selects the most charming croaker and hops over in his direction.