Answered by Diana Lowrey, Archaeologist and Bat Expert, Idaho National Laboratory (This post was originally published on April 15, 2008.)
Bats have evolved to have an exceptional navigation system called echolocation, which helps them to find their prey in the dark. Bats make sounds just like we humans make sounds, by expelling air from the lungs over vibrating vocal chords in the throat to form a sound wave, and this wave can travel long distances through the air. Some bats will emit these sounds from their open mouths, but some can even emit sounds from their nose. Because bats produce extremely high sounds, that is, they have a very high pitch, most echolocation sound is beyond our hearing range, although our pets can hear much of the clicking that they make.
You might have noticed that nocturnal bats generally have very large ears, and these ears act as sound wave receivers, much like a satellite dish. The bat will emit many high pitched squeaks or clicks and they travel through the air as sound waves, which bounce off an insect (or a building or tree) and the bat listens carefully for that echo to return. The bat’s brain is very sophisticated and by determining how long it takes the sound to return, the bat’s brain figures out how far away the object is, and how big it is, and if the object is moving.
Generally, a bat’s chirp (or sound wave) will travel at 741.1 miles per hour, or 0.2 miles per second. If you are lucky, if you stand outside at dawn or dusk when it is just the right temperature, you can see bats performing their acrobatic maneuvers while chasing insects (hopefully they are eating mosquitoes), and hear some of their marvelous clicking sounds.
Sound Waves and Echoes
Sound is made when air molecules vibrate and move in a pattern called waves, or sound waves.
Experiment materials: a Slinky™ (preferably a metal one) and a friend.
- Stretch the Slinky™ out on the floor or a table to about 10 feet with a friend firmly holding the other end. One of you represents the sound source and the other represents the sound receiver (the ear).
- The sound source person gives the Slinky™ a rapid, little push. Did you see the coils of the Slinky™ compress as the wave traveled to your friend (the ear)? This is a longitudinal wave, like a sound wave. Sound waves move through the air with a squeezing and stretching of molecules of air. When a vibration is produced the air around the source of the vibration is pushed together tightly, then stretched out as the squeezed air molecules push away from each other. This motion continues and the longitudinal sound wave moves through the air.
Sound waves can bounce or reflect. This reflection is called an echo.
- Stretch out the Slinky™ again.
- This time, as the sound source person gives the Slinky™ a rapid, little push, watch the wave as it travels along the Slinky™. When it gets to the sound receiver (the ear), notice that the wave will rebound back up the coil to your hand. This represents an echo.