Rat Radar: Rodent Uses Natural "GPS"

John Pickrell in England
for National Geographic News
January 29, 2004

Hikers trekking through unfamiliar territory are well advised to carry a compass, if not a GPS unit, to stay on course. Other animals are lucky enough to have complex navigational equipment in-built. New research reveals that Israel's blind mole rat (Spalax ehrenbergi) uses the Earth's magnetic field on long journeys, much like a compass, to continuously monitor and maintain its course.

But that's not where the burrowing rodent's abilities end. The mole rat also has an uncanny habit of burrowing around obstacles—such as ditches or concrete blocks—without ever coming in to physical contact with them.

"One of the most interesting characteristics of this unique subterranean mammal is that it is [totally] blind," said Tali Kimchi, who studies the brain and behavior at Tel Aviv University in Israel. "This created a strong evolutionary pressure on the mole rat to develop specialized, non-visual mechanisms of orientation that enable it to find its way underground."

Making navigational mistakes underground is expensive business too. Excavating soil uses between 360 and 3,400 times as much energy as moving the same distance above ground.

Internal Map

Israel's blind mole rats live most of their lives underground in pitch-black, complex tunnel systems. They have to dig over great distances when foraging for bulbs and roots, and then have to find their way home again.

Like other rodents, dogs, even people, mole rats can predict where they are simply by keeping track of their own balance and movement, said Kimchi. But over long distances in a mish-mash of winding tunnels, that internal map may not be enough, she said.

Sighted animals use visual landmarks to keep correcting mistakes, but the blind mole rat—which may have lost its eyes in an irreversible evolutionary step up to 30 million years ago—had to be using something else, said Kimchi.

Researchers already knew that a related species, the Zambian mole rat (Cryptomys anselli), could detect the Earth's magnetic field. So, Kimchi along with biologists Joseph Terkel, also in Tel Aviv, and Ariane Etienne of the University of Geneva in Switzerland decided to test if the Middle Eastern species might be using that ability to deftly navigate in the dark.

As they reported online January 21 in the science journal Proceedings of the National Academy of Sciences, the team put wild mole rats into two types of laboratory maze.

One maze was wheel-shaped and made up of eight radial spokes with a central hub. The animals were required to find their way from a feeding place to a nesting box by the most direct route. When the maze was placed between two massive electromagnets—which had the effect of turning the Earth's magnetic field by 90°—the mole rats were much more likely to lose their way.

In a second rectangular maze, the mole rats were tested on their ability to use their internal map along with the magnetic compass to find new shortcuts to a food reward. Again, once the magnetic field was unexpectedly turned by 90°, they were much less likely to discover a shortcut.

Continued on Next Page >>


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