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ROBERT SIEGEL, host:

This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel.

MELISSA BLOCK, host:

And I'm Melissa Block.

There are a lot of theories out there about cows, why they sit down or stand up, or face one direction rather than the other. Now, a new study has identified one major influence on cows, the earth's magnetic field. NPR's Nell Greenfieldboyce has our story.

NELL GREENFIELDBOYCE: Hynek Burda didn't set out to study cows. He's a biologist at the University of Duisburg-Essen in Germany who studies small underground creatures called naked mole rats. They're blind, but have a kind of magnetic compass. They always build sleeping nests in the southern side of their little homes.

Burda wondered if sleeping humans might do something similar. So he decided to look at camping tents and fired up Google Earth on his computer to get an overhead view of campgrounds. Tents were hard to see. But looking around on Google Earth, he realized he could see cows, lots and lots of cows. So he decided to see if they were affected by Earth's magnetic field.

Mr. HYNEK BURDA (Biologist, University of Duisburg-Essen): We just stopped looking on camping people and started to look on cows.

GREENFIELDBOYCE: Over 8,000 cows from pastures all around the world. The results appear in this week's issue of the Proceedings of the National Academy of Sciences. They show that cows tend to face either magnetic north or south when grazing or resting.

Mr. BURDA: Most of them actually align in a north-south direction.

GREENFIELDBOYCE: Regardless of where the sun was or how the wind blew. Now, Burda told one friend about these results, a hunter, who said, well, why don't you also look at deer beds, these oval hollows in the snow that deer make when they're sleeping? And again, it's on the north-south orientation.

Mr. RICHARD HOLLAND (Biologist, University of Leeds): It's a very clever use of Google Earth, and the evidence is quite compelling.

GREENFIELDBOYCE: Richard Holland is a biologist with the University of Leeds in the United Kingdom.

Mr. HOLLAND: It does seem that these animals are detecting the Earth's magnetic field and using it to point in a north-south direction.

GREENFIELDBOYCE: Holland says there's one way to confirm that this is really happening.

Mr. HOLLAND: The next step is to start going out and putting magnets on the heads of cows and horses and deer and everything, to see how that affects them. That's one of the more traditional ways of testing if they have a magnetic sense.

GREENFIELDBOYCE: If they really do have an internal compass, the magnet would mess it up.

Now, some birds use magnetic compasses for navigation, and bats do, too, but Holland says it's not clear what cows or deer would get out of it. He says it may just be a leftover from their ancestors' ancient wanderings.

Nell Greenfieldboyce, NPR News.

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