Hearing Without Ears: How Do Newts and Salamanders Hear Without External Ears?

Problem: How do newts and salamanders hear without external ears?

Materials

• Metal pie pan
• Table salt
• Metal spoon

Procedure

1. Place the pie pan upside down on a table.
2. Sprinkle a very thin layer of salt over the upturned bottom of the pan.
3. Tap on the upturned bottom of the pan with the spoon.
4. Observe and record any difference in the movement of the salt crystals.

Results

Tapping on the pan causes the salt crystals to move around.

Why?

The molecules in the pan that is struck by the spoon start to vibrate (move back and forth). As these molecules move, they bump into neighboring molecules and start them moving, but with slightly less energy. This continues until there just is not enough energy to cause the neighboring molecules to vibrate. Newts and salamanders that walk on land are able to "hear" by feeling vibrations from the surface they stand on. A slender muscle connects the shoulder blade (scapula) to bones set in a thin membrane of the ear cavity in the head. The vibrations from the surface travel up the bone in the front leg to the shoulder blade, through the muscle, and on to the ear. Sounds close to the animal produce stronger vibrations, just like the greater movement of the salt crystals close to the tapping.

Let's Explore

1. Does the surface being tapped affect the vibrations? Repeat the experiment by placing the salt grains on different surfaces-a cardboard box, a wooden table, a plastic dish.
2. How does the distance from the tapped area affect the vibrations? Repeat the experiment tapping on the side of the pan farther from where the salt crystals are spread.

Show Time!

1. How do other creatures without external ears, like fish, "hear"? Fish have a lateral line that runs down the side of their body. It is believed that this line of nerve receptors detects pressure and sound that travel through the water. Demonstrate the movement of waves through water by pouring 1 inch (2.5 cm) of water into a rectangular glass baking dish. Place the dish under a desk lamp and gently touch the surface of the water. Observe and record the movement of the water. Tap on the side of the dish, and determine if the sound is transmitted through the water. Display photographs of the experiment as part of your project.
2. Birds have a keen sense of hearing. Owls can hear and locate their prey in the dark. The robin seems to be able to hear the movement of earthworms underground. Discover more about the ability of birds to receive sound. Display pictures of birds along with any unusual hearing abilities you have noted.
3. Elephants have very large ears and are able to hear faint sounds. Donkeys have the ability to move their ears and are alerted by the slightest noise. Discover more about the size and shape of external ears and how they affect the ability to hear. Display pictures of animals with various sizes and shapes of ears, and indicate their ability to hear.

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Janice VanCleave's Animals
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