Dear Carolyn Grace,
Toothed whales—like dolphins and belugas—might live in the ocean, but they have some big things in common with cave-dwelling bats. They’re all mammals that live in dark places and use echolocation.
That’s why I talked about your question with my friend Christine Portfors. She’s a biologist at Washington State University. Her lab keeps a colony of bats.
Many bats sleep in caves and zoom around at night. Their world is dark, so they use sounds and their echoes to perceive the world around them, which is called echolocation. Toothed whales live in dark oceans or murky rivers and lakes. That’s why they use echolocation, too.
“Whenever there isn’t enough light for an animal to do the things that it needs to do like navigate, collect food and find mates, then it has to use some other sensory system besides vision,” Portfors said. “So, they send out sound. That sound bounces off objects in their environment and comes back as an echo. They use those echoes to identify objects and navigate.”
A bat sends out squeaks from its mouth or nose. A toothed whale sends out clicks from a fatty lump on its forehead. The lump is called the melon.
One of my favorite animals is the river dolphin. It lives in rivers so dark and cloudy that its eyes are useless. Instead of looking where it’s swimming, a river dolphin uses its melon to shoot out clicks. It can tell a lot from the echoes that return.
“An object is going to produce different types of echoes when a sound hits it depending on where that object is in space,” Portfors said. “Is it off to the right or left? Is it straight ahead? Is it up or down? An animal that uses echolocation can figure those things out all because of the way that the sound comes back as an echo.”
Plus, the sounds don’t hit the object in just one spot. If a river dolphin’s clicks bounce off a tasty fish, the sounds hit a bunch of different parts of the fish. When all those echoes bounce back, the dolphin’s brain forms something like a map or image of the fish and what’s around it. It’s a little bit like how we see—but using sound instead of light.
The sounds bats and toothed whales use for echolocation are special, too. Those squeaks and clicks are very high frequency. They’re usually so high that humans can’t hear them at all.
That’s important because sound travels in the air or water as waves. The waves from low frequency sounds are far apart. If a river dolphin used low frequency sounds for echolocation, the sound waves might bounce off big things—like a giant underwater rock. But those waves might go around a little fish. That means no echo. The dolphin would have no idea the fish was there.
The waves from high frequency sounds are close together. They’ll definitely hit the fish and bounce back, so the river dolphin can find its meal.
You could say that echolocation using very high frequency sounds works very whale.