How Owls Spin Their Heads Without Tearing Arteries

How does a great gray owl do that? Now we know.

Martin Meissner/AP How does a great gray owl do that? Now we know.

Martin Meissner/AP

The human neck is a delicate stem. Torque it a bit too much, and the carotid and vertebral arteries can rip, causing deadly strokes. People have torn their neck arteries riding roller coasters, doing yoga, going to the chiropractor, being rear-ended in the car – even leaning back for a beauty-parlor shampoo.

But owls don't have that problem. They can turn their heads 270 degrees, more than twice what a human can safely handle, without any harm. "If a human being was to try to do the same thing, we would dissect our arteries," says Fabian de Kok Mercado.

He wanted to find out why.

Answering that question involved 12 frozen owls and a team of researchers at Johns Hopkins University, where de Kok-Mercado was a graduate student in the Department of Art as Applied to Medicine. Not only did they figure out the secrets of owls' success, de Kok-Mercado's drawings won a first place prize in the National Science Foundation's annual contest for visualizing science.

Click image to see full illustration.

Johns Hopkins/National Science Foundation Click image to see full illustration.

Johns Hopkins/National Science Foundation

First, de Kok-Mercado had to round up some owls. Because they're a federally protected species, he worked through nature centers. They happened to have a stash of frozen owls that had been killed by collisions with cars and other traumas.

The Hopkins researchers thawed the owls, and injected radio-opaque dye into their vessels while moving their necks in a scanner to track the flow in real time. That's different than a typical necropsy, which can leave scientists guessing how vessels work in real life.

Owls have a few things going for them that humans don't, it turns out. Their neck arteries don't thread through every vertebra. And where the vessels do go through bone, the canal is much wider than it is in humans. Those two features make it less likely that bone will collide with delicate tissue and injure it.

But that doesn't solve another big problem — having blood flow pinched off, starving the brain. What really surprised the scientists and illustrator is that owls seem to have taken care of, too.

The arteries at the base of the head widen out into reservoirs, unlike typical arteries that narrow the further they go from the heart. The reservoirs make for more blood flow, even if the arteries are pinched elsewhere. And a trigeminal artery connects the front and back of the brain. De Kok-Mercado says: "The blood is going to keep pumping."

In this case, an illustration is worth a lot more than a thousand words, so check out the prize-winning drawings. De Kok-Mercado is now working at the Howard Hughes Medical Institute, where he's bringing other mysteries of science to light. "So much of the science is visual," he says.

And humans are left knowing that lacking that special owl anatomy, we'd be best off not sticking our necks out.

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How Owls Turn Heads

A mystery of the animal kingdom: how do owls turn their heads 270 degrees without damaging their blood vessels? At last an answer, published this week in Science. Fabian de Kok-Mercado and Philippe Gailloud dissected and x-rayed owls to discover how the birds do the twist.

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IRA FLATOW, HOST:

Up next, Flora Lichtman is here with Video Pick of the Week, fresh from being the recent winner of the Cyberscreen Film Festival. Well, congratulations, Flora.

FLORA LICHTMAN, BYLINE: Oh, thank you, Ira.

FLATOW: It was for optical illusion piece.

LICHTMAN: Yes. Step into an optical illusion was the winner. Thank you. But, really, I mean, I'm still stuck on dung beetles.

(LAUGHTER)

LICHTMAN: That was amazing. Wasn't that amazing? OK. And there are very, very few animal stories could compete with that - what we just heard on SCIENCE FRIDAY. But I actually think that the Video Pick this week is a contender.

FLATOW: This can do it.

LICHTMAN: I think so. So this question, the question of the Video Pick of the Week is how owls can turn their heads almost full circle?

FLATOW: Really?

LICHTMAN: You've seen. You've - I'm sure...

FLATOW: Yeah, I know I tried it, you know.

(LAUGHTER)

LICHTMAN: Yeah. We can't get much past than 90.

FLATOW: Why can they do and we can't is my question.

LICHTMAN: Right. So they can do it 270 degrees. If you try right now at home, you're probably doing 90 degrees maybe, right?

FLATOW: Maybe.

LICHTMAN: OK. So there are a few things.

FLATOW: It's a good yoga (unintelligible). Let me just remind everybody this is SCIENCE FRIDAY from NPR.

Flora, continue with the...

LICHTMAN: Well, yes. So there are two things going on here. One is there's a bone difference between owls and humans. And this is already known. Owls have the double the number of vertebrae in their necks than we do. They have 14 and we have seven, and more segments gives them more flexibility.

FLATOW: Right.

LICHTMAN: You imagine, like...

FLATOW: If you play with any of those kid's constructions that...

LICHTMAN: Exactly.

FLATOW: ...you see the more segments you have, the more you can twist.

LICHTMAN: The more you can twist. So we have a bone difference. But the question that intrigued Philippe Gailloud and Fabian de Kok-Mercado was why don't owls get strokes? And Philippe Gailloud actually studies disease caused by artery damage. And so he knows first-hand that in humans, if you tried to turn your head like that, you would damage your blood vessel that would cause a clot and you might get a stroke. And beyond that, let's say that didn't happen, the other problem is that if you twisted your neck that much, your arteries, which bring blood to your brain, important, would be pinched off. So how to the owls get around this? And that's what these researchers looked into this week, and that's what the Video Pick of the Week is about.

FLATOW: Great. So why don't we see dead owls all over the place from turning their neck?

LICHTMAN: Correct. That's exactly what he said. Why are there not dead owls lying all over the forest for was the way that Dr. Gailloud puts it.

(LAUGHTER)

FLATOW: Well, it's a good question, and he answers it.

LICHTMAN: They answered it.

FLATOW: I mean, yeah. Very beautiful graphics in Video Pick this week.

LICHTMAN: Yes. And I can't take credit for those. Fabian and Philippe were actually the winners of this science visualization challenge, some by the NSF and science, and so you can see the full poster on our site or its blog or you can see the video. But basically, they dissected owls. No owls were harmed in the making of this video. They wanted me to assure everyone.

FLATOW: Yeah, they said that.

LICHTMAN: And also they X-rayed them and they put it contrast eyes. And they found this sort of anatomical differences that would allow owls to do this.

FLATOW: One thing that struck you about the video that they sent as well as it struck me.

LICHTMAN: I think struck you. I'm not sure.

FLATOW: Was that right at the beginning of the video, you watch the video and one of the scientists is there and he's got an owl on his arm. And they're absolutely - they look alike. And now you say people look like their pets. He looks — he's standing still. Both their eyes are facing forward and it looks like - just like his owl.

LICHTMAN: I'm not going to go there. There - I will not go there. They are both starring intensely. It's a beautiful - it's beautiful footage. We have Fabian holding this owl and they actually do this trick where they get owl to do the kind of full rotation of the neck. It's really beautiful. They really came through with (unintelligible).

FLATOW: You know what I didn't realize, which he says in it, I didn't realize about the ability to tilt their heads also, not just to go around in circles...

LICHTMAN: Yes.

FLATOW: ...but how high they can tilt up their head.

LICHTMAN: 180 degrees up too, and this maybe partly because of the way that their arteries are. So they -some of their arteries travel through the vertebrate. But there's a lot wiggle room in there and they seem to be arranged so that there are some slack at the bottom, which allows them to kind of more of this maneuvering than you would expect. And then the other thing is that they found when they injected this contrast eye and took these 3-D sophisticated X-rays that the owls actually pool blood at the base of the head.

Their arteries expand. They become these little reservoirs of fresh blood, so that even if the arteries get pinched off, they have access to oxygenated blood while their heads are turned. And they, of course, they need this. They have huge, you know, brains and eyes.

FLATOW: Right. Right. Yeah. So it's a great video. If you want to know how an owl does this, we have the whole thing right there. It's our Video Pick of the Week up there on our website at sciencefriday.com. Also it's up there on YouTube in our SCIENCE FRIDAY YouTube channel. You could watch it there.

LICHTMAN: Absolutely. Go to YouTube or SCIENCE FRIDAY or download our video podcast and you can take SCIENCE FRIDAY videos on the go.

FLATOW: There you go. And it's made by Flora Lichtman, who is now our correspondent and managing editor for video. Congratulations on your appointment.

LICHTMAN: Thank you. Thank you.

(LAUGHTER)

FLATOW: That's about all the time we have for today.

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