Dear Ella,

Baby frogs go through some pretty big changes to become grown-up frogs. They start out as tiny tadpoles with just a head and a tail to help them swim. They have an inner ear and can hear some sounds. 

As they change from tadpoles to frog-shaped bodies, through a process called metamorphosis, they can hear even better. They can hear croaking, but we aren’t sure if they know when it’s coming from their own mom or just another frog in the pond.

I hopped on over to visit my friend Jesse Brunner at Washington State University to find out more about it. Brunner is a scientist who studies health in communities of amphibians and works with frogs.

At first, I thought all female frogs laid their eggs in the water. I thought they left their eggs alone to become tadpoles, then froglets, and finally frogs. It turns out I was wrong.

dru-hero-pose“In North America, we usually think about tadpoles in ponds,” Brunner said. “But a lot of species hatch directly into frogs.”

Some species of frogs will give their jelly-like eggs a piggyback ride until they hatch. Some frogs, though now extinct, carried eggs in their stomachs. In some species, it’s male frogs that watch over the eggs.

Inside the eggs, tadpoles start developing their front and back legs, a brain, lungs, and the parts they will use to hear.

“During metamorphosis, bones in their heads get rearranged, develop fully, and harden up,” Brunner said.

This process creates the eardrum, or a tympanum. Cats and humans have a typanumum, too. Ours are inside our ears. Some frogs have them on the outside of their head.

Frogs that come straight out of the egg are more likely to be able to hear their parents because their hearing developed while their parents may have been around.

When frogs push air back and forth between their lungs and mouth, it passes over their vocal cords. This is what makes a big croak erupt. The sound travels through water to the offspring’s eardrum. The sound waves vibrate hairs in the eardrum, which are translated into electrical impulses. The brain helps interpret this as sound.

Some frogs sense vibrations in their lungs and mouths to “hear” what is going on around them. Frogs who live near loud streams can’t hear as well, so they also use their feet to wave and get the attention of other frogs.

Frogs’ ears also work closely with their lungs to keep pressure in their ears balanced. It helps them from hurting their own eardrums.

When frogs get together they can create a chorus of croaking so loud, it can be heard from miles away. In fact, it’s actually the males that do most of the croaking. They use it to attract a mate and to produce more baby frogs, starting the cycle all over again.

Dr. Universe

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