How are echoes used?
Some animals find food and other objects using echolocation. Echolocation is the use of echoes, or reflected sound waves, to find objects. Echolocation can be used to locate objects or make ultrasound images. Animals that use echolocation produce ultrasound, which are sound waves that have frequencies higher than 20,000 Hz. The frequencies of these ultrasonic waves are too high for humans to hear. 
Animals that use echolocation can tell how far away an object is by the time it takes for their ultrasonic waves to bounce off an object and return to them, or echo.

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