[RADIOLAB INTRO]

JAD ABUMRAD: Well, I don't know. How would you describe this one?

ROBERT KRULWICH: My sense is that you walk into a wild place and you hear the wind and the trees, and you hear these chirps and sounds and calls, and they're just part of the—they're part of the wild. They're wildlife. But there's now a group of scientists who listen much more closely, and who are reducing wildlife to wild talk. It's—it's ...

JAD: Yeah.

ROBERT: There are words in there.

JAD: When you find the words, as the people we will meet do in these stories, you end up not just understanding, but actually entering that wild space in a very cool way.

ROBERT: Right.

JAD: This is a story, this first one, that we heard about ...

ARI DANIEL SHAPIRO: Yeah, yeah. I'm ...

JAD: ... from Ari.

ARI DANIEL SHAPIRO: I'm Ari Daniel Shapiro. I'm a public radio producer in Boston.

JAD: And Ari recently met a guy. I think a German guy.

ARI DANIEL SHAPIRO: He's Swiss.

JAD: Oh, okay. Sorry.

ARI DANIEL SHAPIRO: His name is Klaus Zuberbuehler.

KLAUS ZUBERBUEHLER: Hey Ari, it's Klaus.

ARI DANIEL SHAPIRO: And he's a professor of psychology ...

KLAUS ZUBERBUEHLER: At the University of St. Andrews.

ARI DANIEL SHAPIRO: Which is in Scotland.

JAD: And where does this story actually take place? Because ...

ROBERT: Where's the jungle?

JAD: Yeah.

ARI DANIEL SHAPIRO: Well, maybe the best place to start is to kind of describe the scene where we are.

JAD: Okay.

ARI DANIEL SHAPIRO: Which is in the Tai forest.

KLAUS ZUBERBUEHLER: Tai forest.

ARI DANIEL SHAPIRO: Which is in the Ivory Coast in Africa.

ROBERT: So it's not in Thailand?

ARI DANIEL SHAPIRO: No, it's not. It's T-A-I.

ROBERT: T-A-I. Okay.

ARI DANIEL SHAPIRO: Yeah. And Klaus describes the jungle as this thick, sensory world.

KLAUS ZUBERBUEHLER: Very dark, very moist, and very, very green.

ARI DANIEL SHAPIRO: And you can't really see for more than 15 to 20 feet.

KLAUS ZUBERBUEHLER: And I mean, sometimes you feel like you walk through a big cathedral of dark trees, and you don't see very much because all the animals, obviously very shy and run away.

ARI DANIEL SHAPIRO: I mean, is it still?

KLAUS ZUBERBUEHLER: [laughs] No, it's—it is very, very noisy.

ARI DANIEL SHAPIRO: It's a din. It's just this kind of sonic chaos.

KLAUS ZUBERBUEHLER: Chaos. All these insects and birds and bats and mammals. It's almost as if they compete for acoustic space. So it is very, very loud. I mean, the main sensation you have in the beginning really is that you're just completely lost.

ARI DANIEL SHAPIRO: So it's 1991.

JAD: All right.

ARI DANIEL SHAPIRO: And he figured he had to start somewhere, so he focused his attention on a kind of monkey.

KLAUS ZUBERBUEHLER: A very beautiful monkey, I think.

ARI DANIEL SHAPIRO: Called the Diana monkey.

KLAUS ZUBERBUEHLER: This mix of black, white, and sort of reddish.

ARI DANIEL SHAPIRO: Diana monkeys live up in the treetops, which can be as high as a hundred feet off the ground.

JAD: Wow!

ARI DANIEL SHAPIRO: They eat fruits and they eat insects, and they're chattering.

KLAUS ZUBERBUEHLER: A cacophony of calls.

ARI DANIEL SHAPIRO: Which to him, of course ...

KLAUS ZUBERBUEHLER: You know, as a newcomer to the forest ...

ARI DANIEL SHAPIRO: ... was all just noise.

KLAUS ZUBERBUEHLER: Just a little bit imagine, like, a child trying to learn a language, which initially must just sound like a string of sounds that you can't really understand, and then, you know ...

JAD: So what did he do?

ARI DANIEL SHAPIRO: Well, he started provoking the monkeys into making different kinds of noises. For instance, he'd walk out into the forest with a boombox ...

KLAUS ZUBERBUEHLER: A speaker.

ARI DANIEL SHAPIRO: ... and play the sound of the Diana monkey's most feared predator: the leopard.

JAD: He would just play the sound into the trees?

ARI DANIEL SHAPIRO: Yep.

JAD: Whoa!

ARI DANIEL SHAPIRO: And all of a sudden ...

KLAUS ZUBERBUEHLER: Suddenly ...

ARI DANIEL SHAPIRO: ... they start leaping around the branches, hopping around.

KLAUS ZUBERBUEHLER: ... you know, you see all this motion, and ...

ARI DANIEL SHAPIRO: And they make this one particular call.

KLAUS ZUBERBUEHLER: You know, these very loud alarm calls.

ARI DANIEL SHAPIRO: This one here.

ROBERT: Meaning what?

JAD: Yeah, are they just saying, like, run, or is it something more specific?

ARI DANIEL SHAPIRO: Well, here's where it gets a little bit more interesting. Next step, he brought that same cassette player out.

JAD: Pointed it at the trees, hit play, all that?

ARI DANIEL SHAPIRO: Yep. But this time he plays ...

KLAUS ZUBERBUEHLER: The shrieks of a crowned eagle.

JAD: Eagles eat monkeys?

ARI DANIEL SHAPIRO: Yeah, they do.

KLAUS ZUBERBUEHLER: They attack from above.

ROBERT: I've heard about them. They're very scary. They come flying in with their talons or their beaks, and they hit you in the head sharply and kill you instantly.

JAD: Oof!

ROBERT: And then you fall to the ground.

JAD: Yeah. And so what do the monkeys do when they hear this?

ARI DANIEL SHAPIRO: They make that sound.

JAD: Same one?

ARI DANIEL SHAPIRO: Well, that's what he thought, but when he went back to the lab and started looking at the sounds on the computer, comparing one to the other: eagle, leopard, eagle, leopard, he realized that they're actually slightly different.

KLAUS ZUBERBUEHLER: In the acoustic details of the calls. And it's something that is very difficult to hear when you really only see it in the spectrogram, which is kind of a visual representation of these calls.

JAD: This is on the computer?

ARI DANIEL SHAPIRO: Yeah.

KLAUS ZUBERBUEHLER: But interestingly, once you've seen that, and once you know what to pay attention to, you go out into the forest and suddenly you do hear these differences, which you haven't heard before.

ROBERT: So you're saying when they hear a call "Leopard coming!" they go up the tree, but when they hear "Eagle coming!" they run down the tree?

ARI DANIEL SHAPIRO: Exactly. Exactly.

ROBERT: So it's really kind of like a word. They—like a word. Now here's an interesting question: I mean, if a French couple were sitting next to me on the subway and they were saying, "Do you know where Sam was last night?" in French, if I don't speak French, I'm outside of that conversation. But a lot of people do speak French, and they can listen to French people talking. The question's then raised: if you live in the forest and you speak chimp or you speak eagle or you speak snake, would you ever be able to overhear or learn something from a neighborly species? In other words, is there an equivalent of listening to the other person talking French in the wild?

JAD: Hmm, good question.

ROBERT: And that brings us back to Klaus.

ARI DANIEL SHAPIRO: Well, Klaus was wondering the same thing. So take those alarm calls, for instance. He wanted to know whether different species of monkeys could understand each other.

KLAUS ZUBERBUEHLER: Right, so ...

ARI DANIEL SHAPIRO: And luckily for Klaus, there's, like, at least 10 different primate species living inside that Tai Forest.

KLAUS ZUBERBUEHLER: So there's ...

ARI DANIEL SHAPIRO: One, colobus monkeys. Two ...

KLAUS ZUBERBUEHLER: Spot-nosed monkeys.

ARI DANIEL SHAPIRO: Three, chimpanzees. Four ...

KLAUS ZUBERBUEHLER: Galagos.

ARI DANIEL SHAPIRO: Five ...

KLAUS ZUBERBUEHLER: Colobines.

ARI DANIEL SHAPIRO: Six, putty-nosed monkeys. Seven ...

KLAUS ZUBERBUEHLER: Mangabey species.

ARI DANIEL SHAPIRO: Eight ...

KLAUS ZUBERBUEHLER: Prosimians.

ARI DANIEL SHAPIRO: Nine ...

KLAUS ZUBERBUEHLER: Campbell's monkey.

ARI DANIEL SHAPIRO: And then the Dianas, 10.

KLAUS ZUBERBUEHLER: Yeah, so it's a very rich primate fauna.

ARI DANIEL SHAPIRO: So Klaus's question was: could Diana monkeys understand the alarm calls of another one of these monkeys, the Campbell's monkey?

JAD: Oh, could they go across monkey lines, so to speak?

ARI DANIEL SHAPIRO: Exactly.

ROBERT: Hmm.

ARI DANIEL SHAPIRO: So he used that same setup from before.

JAD: The speaker thing where he plays the sound into the trees?

ARI DANIEL SHAPIRO: Yeah. And he played the eagle and leopard alarm calls from the Campbell's monkeys to the Dianas to see if they'd react.

KLAUS ZUBERBUEHLER: And what we found to our great surprise was that the Diana monkeys ...

ARI DANIEL SHAPIRO: They understand it.

JAD: Really?

ROBERT: Really?

ARI DANIEL SHAPIRO: Yep.

KLAUS ZUBERBUEHLER: They take that very, very seriously and respond to it very strongly.

ARI DANIEL SHAPIRO: So a Diana monkey hearing a Campbell's eagle alarm call will respond as though there were an eagle, and will respond to the leopard alarm call as though there were a leopard. And vice versa.

KLAUS ZUBERBUEHLER: And it doesn't stop there.

ARI DANIEL SHAPIRO: Klaus started playing the monkey calls to birds.

KLAUS ZUBERBUEHLER: Such as hornbills.

ARI DANIEL SHAPIRO: Yellow-casqued hornbill.

KLAUS ZUBERBUEHLER: It turns out that ...

ARI DANIEL SHAPIRO: They understand it.

JAD: The birds?

ARI DANIEL SHAPIRO: Yeah. These hornbills ...

KLAUS ZUBERBUEHLER: Are capable of discriminating these different monkey alarm calls.

ROBERT: Wow!

KLAUS ZUBERBUEHLER: So it's a pretty substantial web species basically eavesdropping on each other's calls in these forests.

ARI DANIEL SHAPIRO: But Klaus himself, he was still on the outside of it all.

KLAUS ZUBERBUEHLER: It is that general sense of perhaps not really belonging there. But then ...

ARI DANIEL SHAPIRO: He told me about this one day.

KLAUS ZUBERBUEHLER: I was working in the forest.

ARI DANIEL SHAPIRO: He had gone out for the day, and he'd gone out alone.

KLAUS ZUBERBUEHLER: And I was very far away from camp.

ARI DANIEL SHAPIRO: And it was in the late afternoon, and he realized that he should probably be heading back to camp.

KLAUS ZUBERBUEHLER: Because I still had to walk for something like 15, 20 kilometers back to camp.

ARI DANIEL SHAPIRO: And he was walking past a kind of valley.

KLAUS ZUBERBUEHLER: And then I heard on the other side of the valley a monkey group giving leopard alarm calls, which doesn't happen that often.

ARI DANIEL SHAPIRO: It was the first time that he wasn't actively listening, but he heard these monkeys make this call and recognized it.

KLAUS ZUBERBUEHLER: It was absolutely striking.

ARI DANIEL SHAPIRO: And he was actually quite excited by this.

KLAUS ZUBERBUEHLER: Because I was suddenly able to understand what the monkey's trying to say, so to speak.

ARI DANIEL SHAPIRO: Those monkeys had picked up a leopard.

ROBERT: Right beneath that sound, there the leopard would be.

ARI DANIEL SHAPIRO: Right. But, you know, those monkeys were way across the valley.

KLAUS ZUBERBUEHLER: So I didn't really think that much and walked on perhaps, you know, half a mile further down the road.

ARI DANIEL SHAPIRO: And the next group of Diana monkeys, still across the valley ...

KLAUS ZUBERBUEHLER: Start giving leopard alarm codes as well.

ARI DANIEL SHAPIRO: And he kind of took notice of that. And then it happened a third time a few minutes later.

KLAUS ZUBERBUEHLER: What became clear to me very rapidly is that a leopard was ...

ARI DANIEL SHAPIRO: Tracking him.

ROBERT: Oh!

KLAUS ZUBERBUEHLER: Of course, I couldn't see it because it was, you know, dense forest, but I assumed that the leopard saw me. And of course that—it's just one of these moments where you're totally alone, far, far away from camp.

ROBERT: What does he do?

ARI DANIEL SHAPIRO: He kept walking. It happened a fourth group called leopard, and fifth group called leopard. And then the groups stopped calling.

KLAUS ZUBERBUEHLER: The only thing I could think of is to pick up a large branch.

JAD: [laughs] I shouldn't laugh. That's just terrifying.

ARI DANIEL SHAPIRO: Klaus, would that stick have done anything for you?

KLAUS ZUBERBUEHLER: I doubt I really would have been able to do very much with a stick.

ARI DANIEL SHAPIRO: But as he's standing there, stick in hand, he realizes he's just entered the forest. He's become ...

KLAUS ZUBERBUEHLER: The 11th primate.

JAD: The 11th primate.

ARI DANIEL SHAPIRO: Because there are those 10 other species of primate, and now ...

KLAUS ZUBERBUEHLER: I mean, suddenly I shifted from being the objective observer to being a sort of part of that whole crowd in there. Even though we're separated by 20, 30 millions of years of evolutionary history, you know, these humble creatures were able to teach me something about what was going on in the forest. And I mean, of course it wasn't intentional. They weren't trying to inform me or anything like that, but it was a very emotional experience.

JAD: So what happened? I mean, obviously he didn't get eaten. What happened?

ARI DANIEL SHAPIRO: Well, he made it back to camp. And he's not sure what happened to the leopard. The leopard must've slinked off into the forest. In the end, it became ...

KLAUS ZUBERBUEHLER: Just another story to tell each other over beers in the evening, I suppose.

JAD: Yeah.

ROBERT: Yeah.

KLAUS ZUBERBUEHLER: Yeah.

ROBERT: Thanks for that story to Ari Daniel Shapiro, our correspondent.

JAD: And also thanks to Klaus Zuberbuehler and Con Slobodchikoff. I'm Jad Abumrad.

ROBERT: I'm Robert Krulwich.

JAD: And we'll be right back.

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