How do bats find their way in the dark?

1. At sunset, bats pour out of their cave to hunt insects. Bats can see, but at night it is very dark. They have a better trick.
2. The bat makes a call. The sound spreads out like ripples. It is so high that people can't hear it. We call it ultrasound.
3. When the sound hits a moth, some of it bounces back toward the bat. That bounced sound is an echo, and the bat's big ears catch it.
4. A near moth's echo comes back quickly. A far moth's echo takes longer, because the sound has farther to travel. The bat can tell the difference!
5. An echo from one side reaches the nearer ear a tiny bit sooner and sounds a bit louder there. That tells the bat which way the bug is.
6. As it closes in, the bat calls faster and faster to keep track of the moth. Then it scoops the moth up with its wing or tail. Dinner!

Tap each part of the bat to see how it helps it hunt with sound.

• Mouth and voice box. The bat's voice box makes very loud, very high calls, and they come out of its open mouth. People can't hear most of them.
• Nose leaf. Some bats call through their nose instead of their mouth. A leaf-shaped flap around the nose helps point the sound forward, like a flashlight beam.
• Big ears. Big ears catch quiet echoes, like cupped hands. The bat can turn them to listen in different directions.
• Tragus. The tragus is a small flap inside the ear. Echoes from above and below bounce off it a little differently, so it helps the bat tell up from down.
• Brain. The brain measures how long each echo took to come back. A short time means close, a long time means far. It turns echoes into a picture of the cave.
• Eyes. Bats are not blind. They use their eyes for long distances and at dusk, and their echoes for close-up hunting in the dark.
• Wings. A bat's wing is a hand with very long fingers. Stretchy skin between them makes the wing. Bats can bend their fingers to twist and turn fast.
• Tail pouch. Skin between the legs and tail can curl into a pouch. Some bats scoop insects into it, then grab them with their mouth.

Send clicks into the dark cave. Move the moth near and far. Watch the echo clock: when does the echo come back?

Experiment: If the moth is farther away, when does its echo come back?

1. Put the moth close to the bat and press Click!
2. Watch where the echo mark lands on the echo clock.
3. Move the moth far away and click again. Compare.

What we found: The farther away the moth is, the later its echo comes back, because the sound has to travel there and back again. Bats use this to judge distance.

Turn on JavaScript to try it yourself.

Click to find the moths and rocks with echoes. Catch 4 moths before the cave ends, and try not to bump the rocks.

Sound is a wave that travels through the air. When it hits something, part of the sound bounces back. That bounced sound is an echo. You can hear echoes yourself if you shout in a big empty hall or near a cliff.

Bats use echoes all the time. An insect-eating bat makes calls many times a second while it flies. Most of the calls are so high that people can't hear them. Each echo tells the bat that something is out there.

The time the echo takes is the clue. Sound travels fast, but not instantly. A moth that is close sends its echo back very quickly. A moth that is far away sends it back later. The bat's brain measures this tiny difference.

Two ears tell the bat the direction. An echo from the left reaches the left ear first and sounds a little louder there. Bats aren't the only animals that do this: dolphins and some whales use echoes underwater, and ships use the same idea, called sonar.

Key words

Echo

Sound that bounces off something and comes back.

Echolocation

Finding things by making sounds and listening to their echoes.

Ultrasound

Sound too high for people to hear.

Frequency

How high or low a sound is.

Feeding buzz

The very fast run of calls a bat makes just before it catches an insect.

Sonar

A technology that uses echoes of sound to find things, usually underwater.

Check your thinking

1. What is the sound that bounces back to a bat called?

   Show the answer

   An echo. Sound that bounces off something and comes back is an echo.

2. Are bats blind?

   Show the answer

   No, bats can see. All bats can see. Many use echoes too, for hunting in the dark.

3. A moth is far away. Compared with a near moth, its echo comes back...

   Show the answer

   Later. The sound has to travel farther there and back, so it takes longer.

4. How does a bat know if a moth is on its left or right?

   Show the answer

   The echo reaches one ear first and louder. The ear on the moth's side hears the echo a tiny bit sooner and louder.

5. What does a bat do as it gets very close to a moth?

   Show the answer

   Calls faster and faster. Fast calls give fast updates, so the bat can follow the moth's dodges.

6. Which other animal also finds things with echoes?

   Show the answer

   Dolphins. Dolphins and some whales click underwater and listen for echoes.