RENEE MONTAGNE, Host:
Most scientists say that one of the key distinctions between humans and other animals is our ability to use language. Today, we have a story that blurs the boundary between human language and animal noises, and it comes to us from our friends at Radiolab.
(SOUNDBITE FROM RADIOLAB)
JAD ABUMRAD: Hey, Renee.
MONTAGNE: That's Jad Abumrad, from WNYC.
ROBERT KRULWICH: And this is me, Robert Krulwich. Radiolab is a show where we get curious, and we explore ideas.
ABUMRAD: Yeah, and sometimes we talk to animals.
MONTAGNE: OK.
ABUMRAD: Well, not really. But we do have a story about a kind of animal talk.
KRULWICH: We ran across it not in dolphins and not in chimps, but in the prairie dog
ABUMRAD: Woo.
(SOUNDBITE OF MUSIC)
ABUMRAD: Prairie dogs.
KRULWICH: So here's the thing: Prairie dogs are these little, rodent-like animals. They live under the ground, in burrows. And when their community is invaded, they - you know - pop out of the burrow...
(SOUNDBITE OF POPPING SOUNDING EFFECT)
KRULWICH: ...and they go, uh-oh. Here comes the - whatever.
P: Sounds kind of like chee-chee-chee-chee.
(SOUNDBITE OF A PRAIRIE DOG CHIRPING)
ABUMRAD: So we spoke with this guy...
P: My name is Con Slobodchikoff, professor emeritus at Northern Arizona University.
ABUMRAD: ...who's spent a whole lot of time...
P: Sitting out in the colonies.
ABUMRAD: ...recording prairie dog calls. And he now believes that these simple, little rodents are like nature's wordsmiths.
P: Well, the thing is that, initially, I recorded...
ABUMRAD: For instance, he began by telling us that the prairie dogs have different kinds of chee's.
KRULWICH: Different warning cries.
P: For different kinds of predators.
ABUMRAD: For example...
P: Humans, coyotes...
KRULWICH: And...
ABUMRAD: Dogs.
P: Right.
ABUMRAD: Is this the kind of thing that we would actually be able to hear the difference between the calls?
P: I'm guessing that you could hear the difference.
KRULWICH: You want to try it, Jad?
ABUMRAD: Soren, could you just play those samples?
SOREN: All right, so here's one.
(SOUNDBITE OF PRAIRIE DOGS CHIRPING)
SOREN: This is another one.
(SOUNDBITE OF PRAIRIE DOGS CHIRPING)
KRULWICH: All right.
ABUMRAD: OK.
SOREN: Here you go. This is a third.
(SOUNDBITE OF PRAIRIE DOGS CHIRPING)
ABUMRAD: Those represent different predators?
P: Yup.
KRULWICH: I - I don't - I can't tell the difference.
ABUMRAD: Can you? I mean, do you know what they are?
P: Human, dog, coyote.
KRULWICH: Oh.
ABUMRAD: Wow.
(SOUNDBITE OF MUSIC)
MONTAGNE: So guys, wait. How does he - I mean, what difference is he hearing?
KRULWICH: Well, he told us at first that, like us, he couldn't tell the difference. But then he took the sounds back to his lab.
P: Where we had a machine that allowed us to measure a series of frequency and time elements in the call.
KRULWICH: And what this computer does is, it takes the sound that the prairie dogs make, and it essentially looks inside for the ingredients inside the sound.
MONTAGNE: And what does that mean?
(SOUNDBITE OF LAUGHTER)
ABUMRAD: Well, it's kind of hard to hear with the chirp. But let me demonstrate with a different sound...
(SOUNDBITE OF A SOUND WAVE HUM)
ABUMRAD: ...which to us sounds like a solid piece of noise.
MONTAGNE: OK, yeah.
ABUMRAD: If you take away all of the high frequencies...
(SOUNDBITE OF A SOUND WAVE HUM)
MONTAGNE: It just - it becomes like a low, bass buzz.
ABUMRAD: Yeah, exactly. But now, if you add those high frequencies back in really slowly...
(SOUNDBITE OF A SOUND WAVE HUM)
MONTAGNE: Yeah, OK.
ABUMRAD: You'll start to hear these hidden overtones just pop out.
(SOUNDBITE OF A SOUND WAVE HUM)
MONTAGNE: Uh-huh. So these sounds are kind of hidden in that original sound?
ABUMRAD: Exactly. So in other words, this sound...
(SOUNDBITE OF A SOUND WAVE HUM)
ABUMRAD: ...is filled with little ghost notes that we can't hear. And certainly, the same is true of this sound.
(SOUNDBITE OF PRAIRIE DOGS CHIRPING)
ABUMRAD: Except in the case of the prairie dogs, it seems their ears are tuned to hear all the different sounds within the chirp. It probably sounds to them like this whole layer cake of tones.
KRULWICH: And Con's computer noticed that the noise they made when a human walked through their village was different in tone from the noise they made when a coyote walked through their village. It was consistently different.
P: But there was a problem.
KRULWICH: When he zoomed in on the oh-oh-here-come-the-human calls...
(SOUNDBITE OF PRAIRIE DOGS CHIRPING)
KRULWICH: ...these ones here.
ABUMRAD: He saw that from one human call to the next, there was a lot of subtle variation.
P: Much, much more than I would expect.
KRULWICH: And that's when it hit him.
ABUMRAD: What if...
KRULWICH: What if...
ABUMRAD: What if...
P: What if they could be describing the individual humans?
KRULWICH: Oh.
P: Now, at that time, no one suspected that this might even be a possibility. But I thought well, let's try it and see what happens.
ABUMRAD: So Con recruited four humans.
KRULWICH: And he had them dress exactly the same: same boots, same blue jeans, same sunglasses - everything the same, except the color of their shirts.
P: We had a person in a blue T-shirt; a person in a green T- shirt; person in a yellow shirt; person in a gray shirt.
ABUMRAD: Then he asked each of them to walk through the prairie dog village.
(SOUNDBITE OF FOOTSTEPS)
KRULWICH: One by one.
(SOUNDBITE OF PRAIRIE DOGS CHIRPING)
ABUMRAD: Prairie dogs made their chirps.
P: And when we analyzed the results, there were significant differences.
ABUMRAD: Like, what kind?
P: They essentially clustered around the colors.
(SOUNDBITE OF MUSIC)
KRULWICH: Does that mean you think you can hear them saying: Here comes the human in blue...
P: Right.
KRULWICH: ...versus here comes the human in yellow?
P: Right.
MONTAGNE: Wow.
ABUMRAD: Really?
P: Oh, I was astounded.
MONTAGNE: That's pretty cool.
P: I was astounded.
KRULWICH: Then he was like well, wait a second. These humans, they're not just different in their shirt colors. They're different in all kinds of ways.
P: Some of the humans were taller. Some of the humans were shorter.
ABUMRAD: So he went back, re-analyzed the chirps, looked a little more closely.
P: And...
ABUMRAD: He realized...
P: We could tease out...
ABUMRAD: The prairie dogs were also commenting about...
P: The general size of the human. Essentially, they were saying, here comes the tall human in the blue; versus here comes the short human in the yellow.
KRULWICH: And then, almost to kind of top himself, he says, OK - if they can do colors and they can do shapes of animals, how about something totally abstract...
P: And it was just...
KRULWICH: ...not from nature?
P: ...off-the-wall idea at that time.
KRULWICH: He went back into the prairie dog field, and he built two large, wooden boxes.
P: Sitting on stilts.
ABUMRAD: A good distance from each other.
P: A hundred and fifty feet. And we strung wires between the two towers.
KRULWICH: His team then made cardboard cutouts of three different shapes.
P: A circle, a square and a triangle.
KRULWICH: And then they ran them out along the wire - kind of like laundry, fluttering above you in the breeze.
P: Each shape would emerge from one of the tower blinds...
(SOUNDBITE OF LAUGHTER)
P: ...and fly something like about three feet over the prairie dog town. And what we found was that the prairie dogs could tell the triangle from the circle very easily. But they could not seem to tell the difference between a square and a circle.
ABUMRAD: Huh. Why not?
P: Well, my guess is that triangles kind of look like hawks.
ABUMRAD: Mm.
P: Circles and squares kind of look like terrestrial predators.
ABUMRAD: Nonetheless, what you've got here is a little rodent with a remarkably big vocabulary, including - but probably not limited to - short, fat, skinny, tall, blue, green, yellow, gray, coyote, human hawk, triangle and/or square.
KRULWICH: Yay.
ABUMRAD: Not bad.
(SOUNDBITE OF MUSIC)
MONTAGNE: You guys, that is so cool.
KRULWICH: It is.
MONTAGNE: I mean, prairie dogs.
KRULWICH: Yeah. And Con says this is the most sophisticated form of animal communication ever recorded.
ABUMRAD: And we should say, he also thinks maybe other animals can do this kind of thing. It's just really hard to capture - record - and figure out what's going on.
MONTAGNE: Well, thank you both for sharing that one with us this morning.
ABUMRAD: Our pleasure. Thanks, Renee.
KRULWICH: You're welcome.
MONTAGNE: This is MORNING EDITION, from NPR News. I'm Renee Montagne.
STEVE INSKEEP, Host:
And I'm Steve Inskeep.