by Linda Rahm, art by Brian Biggs
Dolphins listen for an echo to tell them the location of things in their watery world. And not just location. They can also sense size, shape, and texture. With echolocation, a dolphin can know that there is a three-inch steel ball 100 yards away, or that a single teaspoon of water is being dropped into its tank.
Here's how it works. From a place on the dolphin's head called the “melon,” it sends out rapid, ultrasonic clicking sounds—up to 700 clicks per second—in a focused beam of sound that echoes back when it encounters an object. Like a bat or a submarine, the dolphin is using a form of sonar, or “SOund NAvigation and Ranging.”
Echolocation is so powerful that it lets dolphins “see through” things. They can detect a “mystery object” inside a box underwater and later match it with an object they see above water.
Echolocation helps dolphins find prey hiding under rocks. Some researchers think that the high-speed sound waves may even stun the fish!
- A system or device like radar that uses reflected sound waves for detecting and locating underwater objects.
- A sound frequency that cannot be heard by the human ear.
- Think about the time of day when bats are active. Why do you think a bat uses sonar?
[anno: Bats are active at night. They probably do not have very good vision, so sonar helps them to find prey, such as insects.]
- Think about how far down in the ocean a submarine can travel. Why would a submarine need to use sonar? Write a sentence or two for your answer.
[anno: Answers will vary but could include that a submarine uses sonar because it would be too dark to see anything through a window at a certain depth.]
- Invent a use for sonar, or think of another use for sonar. Think of a way that sonar would be useful for another kind of vessel. Where does the vessel travel? What would sonar help the vessel to do? Write a sentence or two to explain your answer.
[anno: Answers will vary. Students may write that ships could use sonar to help them avoid running aground.]