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STEVE INSKEEP, host:

Somebody may be holding a grudge against you right now and you may not even realize it. To tell us about that somebody - or rather something - we've brought in NPR science correspondent Robert Krulwich once again. Robert, welcome back to the program.

ROBERT KRULWICH: Thank you. Steve, this is kind of a puzzle. People like Professor Kevin McGowan of Cornell…

Professor KEVIN MCGOWAN (Cornell University): Yes, speaking.

KRULWICH: Hey, there. And is this Professor John Marzluff of the University of Washington?

Professor JOHN MARZLUFF (University of Washington): It is.

KRULWICH: Okay. So, both these guys have spent their adult lives studying crows. They're crow scholars.

Prof. MCGOWAN: Yes.

Prof. MARZLUFF: Yeah.

KRULWICH: Yet I am told that no matter how much you study crows, know crows and love crows, when crows get together in a crow group, you guys cannot tell one crow from another. People can't tell crows apart.

Prof. MARZLUFF: Oh, that's absolutely true.

Prof. MCGOWAN: Yes.

KRULWICH: And yet while we cannot tell one crow from another, crows can tell people apart?

Prof. MARZLUFF: Yeah, that's right. They're much better at it than we are.

Prof. MCGOWAN: We just can't do it as well as they can.

(Soundbite of birds squawking)

KRULWICH: Professor McGowan says when he handles a baby crow, which he does -he goes up to nests to band them - the little crow will look at him angrily.

Prof. MCGOWAN: Well, when you're holding them, yeah, they don't look any too happy, and they do more than just look at you. They try to bite you when they can, too. And then, of course, the baby crow starts to squawk, which sets the parents squawking and then the neighbors squawking and then the squawks attract more squawkers.

KRULWICH: Then suddenly you've got 20, maybe 30, birds screaming?

Prof. MCGOWAN: It's like they don't really know why.

KRULWICH: Now, the whole neighborhood now hates you, right?

Prof. MARZLUFF: Most of my neighbors hate me.

KRULWICH: I'm referring to the crow population.

Prof. MARZLUFF: Oh, the crows. Oh.

KRULWICH: Yeah.

Prof. MCGOWAN: Crows are extremely responsive to other crow behavior. They learn from the reactions of other crows.

KRULWICH: And here's the fascinating part: Once a crow sees another crow squawking at a person, yes, they join in automatically, but somehow they will also remember that person that they're squawking at. So, should they see you again, they're going to squawk at you again, which will warn a whole new set of crows in that next place you're a bad guy. So now you've got a whole new set of crows that have learned to hate you.

And so Professor Marzluff says that after he banded some baby crows near the University of Washington, everywhere he went across the campus, whether he went to an automatic teller at the local bank…

Prof. MARZLUFF: And if I go and play tennis in the neighborhood court, if I walked around the block, if I walk over to my neighbors, there are several individuals that will scold me, regardless of what I'm doing.

KRULWICH: And Professor McGowan says after he banded some crows near Ithaca, New York, he could be downtown, very far from any crow nest…

Prof. MCGOWAN: And a crow looks down and he sees me and starts yelling. And, I mean, I'm walking on the sidewalk.

KRULWICH: Or he could be in a public park. He could be mingling with other people, and then a bunch of crows would suddenly appear…

Prof. MCGOWAN: They would come out of the woods and circle overhead, yelling at me.

KRULWICH: No.

Prof. MCGOWAN: And you have to understand, this is a public park with - had this softball complex in, hundreds of people that came there. And, you know, you get kind of paranoid after a while, 'cause everywhere I'd go the crows would be yelling at me. And they wouldn't be yelling at other people, and you just kind of get paranoid.

(Soundbite of laughter)

Prof. MCGOWAN: And it's not just being paranoid. It's also, it's lonely being hated, you know?

(Soundbite of laughter)

KRULWICH: But I - I still don't understand how they do this to you. How do they know who you are when you don't seem to be able to know who they are?

Prof. MCGOWAN: I don't know. At this point, I don't know. Certainly, the crows can do a remarkable job at telling us apart, and we stink at telling them apart.

KRULWICH: Well, one way to get into this question, thought Professor Marzluff, is to figure out whether it's our smell or our shape or our voices, our hair. What is it about us that crows focus on? The obvious candidate is, of course, our face. So, in Seattle, Marzluff bought a mask.

Prof. MARZLUFF: I had picked a caveman mask that was readily available for 10 bucks or something.

KRULWICH: And while wearing that mask…

Prof. MARZLUFF: This extreme face…

KRULWICH: John Marzluff banded some little crows. So the crows could see the mask and learn to fear it and hate it. Then, who did he put the mask on?

(Soundbite of laughter)

Prof. MARZLUFF: That's a great question. Anybody who will wear it.

KRULWICH: He gave it to old people, young people, bald people, hairy people, female people, male people.

Ms. HEATHER CORNELL (Graduate Student, University of Washington): So they had different body sizes, different clothing.

KRULWICH: Different ages.

Ms. CORNELL: Yeah.

KRULWICH: But what they all had in common was that single, caveman face. So, with his graduate student, Heather Cornell, Marzluff asked people who had never touched a crow to walk through the campus wearing the caveman mask. And with the caveman mask, whoever was wearing it, over and over and over…

Prof. MARZLUFF: All of the time, some birds would scold whoever was wearing that caveman mask.

KRULWICH: All of the time?

Prof. MARZLUFF: All of the time.

Ms. CORNELL: So we figured they're focusing in on the facial region.

KRULWICH: It was a logical conclusion. But then how do you know for sure that it's not something about plastic or just the mask-ness? So, as a control, John bought a Vice President Cheney mask, which was never used to band crows, and then he gave the Cheney mask to people. When they wore that mask…

Prof. MARZLUFF: Well, we consistently got strong reactions from the students on campus…

(Soundbite of laughter)

KRULWICH: No, no, no, no, no, no, no. I'm just interested in crows, here.

Prof. MARZLUFF: Oh, the crows. Well, very, very low response rate - orders of magnitude lower.

KRULWICH: So the crows overwhelmingly reacted to the face that once threatened a crow - the caveman face, not the Dick Cheney face. And then maybe the strongest evidence that crows really do concentrate on faces: when John Marzluff asked some of his people to rotate the mask, to wear the caveman mask on their face upside-down, crows who passed by turned upside down to look.

Prof. MARZLUFF: They often turned their head upside down and they'd look at us when we had that mask on.

KRULWICH: (unintelligible) They were doing this in flight?

Prof. MARZLUFF: They would do it in flight, and they would still scold that face.

(Soundbite of birds squawking)

KRULWICH: So, okay. We can say that crows maybe recognize individual humans by our faces, but the question remains why. Why can they do that when we have such trouble doing it to them? Professor Marzluff says it's because crows need to know about human difference.

Prof. MARZLUFF: They have to know a good person from a bad person, because in a given neighborhood, one person might feed them and another person might shoot them - and that literally happens in my neighborhood. And so it pays for a crow to pay attention.

KRULWICH: While we people, we are not threatened or helped by individual crows, so they do need to know about us, but we don't really need to know about them individually, which may help explain why, says Professor Marzluff, they notice us but we just don't notice them.

Prof. MARZLUFF: That's right. That's a great paradox.

INSKEEP: One of the scientists who spoke with NPR science correspondent Robert Krulwich, who's still with us. And, Robert, I want to make sure I understand this. You're saying that people cannot tell crows apart, even if we try?

KRULWICH: That's what I'm saying. I could put you to the test, if you like.

INSKEEP: Okay.

KRULWICH: We have on our Web site kind of a crow line-up. Why don't you go ahead and look? And on the site, we will give you a picture of a crow, an individual crow. You can look at it, study it as long as you like. Try to familiarize yourself with that crow.

INSKEEP: That is a charming crow. You want to have this crow as a pet.

KRULWICH: Look closely at it, now.

INSKEEP: I'm looking closely.

KRULWICH: And when you're ready, click. And that same crow, your crow, will appear - it's going to be a different photo this time. But that crow will appear in a lineup of other crows. And just see if you can tell your crow from the other crows.

INSKEEP: Okay. I've got a guess. Here we go. I'm going to pick number two out of six. Correct, yes.

(Soundbite of laughter)

INSKEEP: Yes.

KRULWICH: I want the national audience to understand it's very unusual. Try it again, Steve.

INSKEEP: It says try another crow. Try another - okay. Another one. Oh, this is a tough one. This is a tough one, but I am going to pick number five. Oh, that time I was wrong.

KRULWICH: Try it again.

INSKEEP: Okay, fine. Well, I get to keep picking? I'm just picking them all.

KRULWICH: Yeah, you can keep going. Yeah.

INSKEEP: Okay. There were go, correct after four tries.

KRULWICH: And you can do this, by the way, at home, if you like. All you have to do is go to our fabulously just brand newly redesigned Web site. It's called now npr.org. It was always called that, but it's better looking.

INSKEEP: NPR science correspondent Robert Krulwich on NPR News.

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