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MOO-VING NORTH?New analyses of Google Earth images hint that herds of cattle, in general, line up with Earth’s magnetic field. Full Storytenback/iStockphoto

In a forest, the north side of a tree is covered with moss. But if you’re lost in an open field, look to the deer to point you in the right direction.  

Herds of grazing and resting deer and cattle tend to align themselves with Earth’s magnetic field lines, a hint that the large mammals can somehow sense the invisible field, a new analysis suggests.

The new findings come from field studies and analyses of satellite images. Although most individual cows and deer in a group aren’t perfectly aligned with the planet’s magnetic field, the entire herd, on average, points either toward magnetic north or magnetic south, says Hynek Burda, a zoologist at the University of Duisburg-Essen in Essen, Germany. He and his colleagues report their results, which they describe as a phenomenon that herdsmen and hunters hadn’t previously noticed, in an upcoming issue of Proceedings of the National Academy of Sciences.

In their field studies, the researchers observed almost 3,000 deer from two species — red deer, Cervus elaphus, and roe deer, Capreolus capreolus — under a variety of climatic conditions at 241 sites in the Czech Republic. Individuals in a grazing herd were generally aligned to face magnetic north. That orientation didn’t consistently line up with any aspect of the terrain on which they were grazing, the direction from which the wind was blowing or the direction from which the sun was shining, Burda says. In fact, many of these field observations were made at night, he notes.

Other field data, such as the orientation of the impressions that the deer made when lying in snow, bolster the idea that deer face north when resting.

Data for cattle, Bos primigenius, came from 308 herds captured in images posted on Google Earth. Altogether, these herds included more than 8,500 cows on all continents but Antarctica, Burda says. The average orientation of each herd didn’t line up with climatic phenomena or with true north but did closely match either magnetic north or south.

Many creatures have a proven ability to sense Earth’s magnetic field, says John B. Phillips, a sensory biologist at Virginia Tech in Blacksburg. After first noting the ability in migratory birds, researchers have discovered that creatures as diverse as blind mole rats (SN: 2/14/04, p. 110), spiny lobsters (SN: 1/4/03, p. 4), chickens, amphibians and fly larvae can also detect the magnetic field. Apparently, Phillips notes, the ability to detect the magnetic field “plays a fundamental role in spatial perception” and may help creatures navigate through their environment, even if they move only over short distances.

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