Guess How Whales Hear!

Resource for Grades K-5

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Running Time: 5m 58s
Size: 17.7 MB

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In many ways life in the ocean is very different from life on land. One of the most important differences is in visibility. On a clear day on land, it is possible to see 10 miles or more. Under water, even in rare instances when light and water conditions are ideal, visibility may be only a few hundred feet. Another difference is in the way sound travels. Sound carries better in water, traveling much farther and about five times faster than in air.

Because of these differences, many marine animals have adapted to life under water in ways that emphasize sound and their sense of hearing, while de-emphasizing sight. Dolphins and whales, or cetaceans as they are known collectively, specialize probably more than any other type of marine animal in their use of sound. Not only do they hear very well -- some species hear more than 50 percent better than humans do -- but many have also evolved vocalizations specialized for communication, navigation, and locating food.

Communication is probably the most important use of sound among cetaceans. Using clicks, whistles, and songs, often in combination, whales and dolphins keep tabs on members of their family or social group. This is especially important during long-distance migrations, in the middle of chaotic feeding frenzies, and more regularly simply to reassure members of the group that all are present and accounted for.

Many marine mammals also use sounds to navigate through their environment and to find food. In a manner similar to bats, some whales and dolphins use what scientists call echolocation to learn about the size, shape, and distance of objects around them and to navigate through their surroundings. They do this by emitting high-frequency clicks and whistles and then listening for those sounds to echo, or bounce off, nearby objects. In a whale or dolphin's mind, vocalizations bouncing off of structures on the ocean floor sound much different from those bouncing off of a school of fish or squid. In fact, many species possess such highly attuned echolocation abilities that they are able to find and catch prey at great depths, where a lack of light renders their sense of vision useless.

The research of Dr. Darlene Ketten, the scientist featured in this video segment, is helping to explain both how cetaceans hear and what they hear. This is important because our oceans are becoming increasingly polluted with human-made noise -- from freighters in crowded shipping lanes, underwater drilling and explosions, and sonar devices used by the military -- and this noise may be negatively impacting many species of cetaceans. In fact, some whale strandings, or beachings, may be related to ear damage or confusion caused by underwater noise. Understanding the impact human activity is having on cetaceans may help to save these important creatures, and this is one of the goals of Dr. Ketten's current research.

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Discussion Questions

What evidence did the whale expert gather suggesting that fat pads were involved in whale hearing?

How is whale hearing similar to human hearing? How is it different?

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Transcript

NARRATOR: (whales singing) Just listen for a minute. (whale song continues) (rapid clicking begins)

DARLENE KETTEN, Marine Biologist, Woods Hole Oceanographic Institute: Most people think that the ocean is silent, that it's something very quiet and dark. And that's completely wrong. The oceans are a very noisy place. You've got earthquakes going on, you've got volcanoes going off, and the noisiest thing in the ocean are the animals themselves. You put your head in the water, you hear lots of crackling noises. Well, those are actually shrimp, making clicks with their... with their claws. Fish are croaking, groupers are making booming noises—big gulpers—and then, of course, whales. (splash)

NARRATOR: Whales hear all of these sounds, including the ones they make. (whale song begins ) And they hear loads better than we do.

KETTEN: These animals hear really well underwater. (whistles) They hear underwater, at depth, under pressure. How do they do that?

NARRATOR: Answering questions like this is Dr. Darlene Ketten's job. (Darlene Ketten, PhD, Woods Hole Oceanographic Institution) She's a marine biologist who works hard and loves her work. (whale sings single note)

KETTEN: This is probably as close as I'm ever going to get to outer space. I would love to go to another world. Three-quarters of this planet is covered with another world.

NARRATOR: Hearing well is even more important in this other world than it is in ours on land.

KETTEN: The oceans are perpetually dim. Light doesn't penetrate water that well, so if they use their eyes primarily, they wouldn't get much information.

NARRATOR: (whales sing shrilly) All animals need to know where their food is, where their family is, where there might be danger. If you can't see these things, you listen for them.

KETTEN: If you think about it, you both actively and passively listen. If I'm not boring you, you're actively listening to what I'm saying. But if somebody in the background says your name, you'll hear it, because your ears are monitoring the world.

NARRATOR: And so are the ears of whales. (whale sings) But where are those ears? We can't see them. We call what's on the outside of our head an ear, but that's not the hearing part. The hearing part is on the inside, for us and for whales.

KETTEN: This is us, and our ears are in here, in this little bone right in this immediate area. But, this is a blue whale ear. This is just the blue whale ear, and as you can see, it's an ear that's just about the size of our head.

NARRATOR: (whale singing) These giant ear bones, and our tiny ear bones, get sound to the brain. That happens inside our skulls. We have open ear canals that let sound into our ear bones, but whales and dolphins don't. Without an ear canal, how does sound get in? Dr. Ketten really wanted to know.

KETTEN: Scientists have to be both nosy and curious—I want to know what happened. I want to know why it happens. I want to know how it happens.

NARRATOR: She looked at the insides of dozens and dozens of whale and dolphin heads. She noticed something strange inside their heads—long packets of fat leading to their ear bones.

KETTEN: So they've got these canals that are kind of like rabbit ears, except they're long ones going out their jaws, and if... Sometimes you'll see a dolphin, if it's listening, it's turning its head—well, that's just like turning our heads like this. It's moving these fats that lead to their ears so that it can use, like, antenna to pick up differences in the sound. So, how does the sound get into the head? Through the skin, into these fat channels that are evolved over 50 million years.

NARRATOR: That was Dr. Ketten's idea, her hypothesis.

KETTEN: The idea of a hypothesis is that you think you know the explanation for a phenomenon, and then you test it, and see whether or not your hypothesis holds true. If it doesn't, go back to square one and learn from the mistake where it went wrong, how you have to change that hypothesis.

NARRATOR: So she tested her hypothesis over and over, and it turned out to be right.

KETTEN: There's that little sudden spark of (claps hands), "That was right!" or "Ah, I got it!"

NARRATOR: But scientists' ideas are not always right.

KETTEN: I don't think I'm queen of the universe and get to always be right. That's exactly not the case. In fact, the most interesting things are... are when you're very wrong and you find out a new surprise.

NARRATOR: So now that Dr. Ketten knows how whales hear, what do you think she'll try to learn about whales next?