Hamburg, Germany (dpa) - Grazing cows tend to face the North and South Poles, according to German scientists who studied 308 herds using Google Earth satellite photos.

The Boreal bovine orientation suggests that they, like migratory birds, sea turtles and monarch butterflies, tune into Earth's magnetic fields, says Hynek Burda, a biologist at the University of Duisburg-Essen, Germany.

The findings, published in New Scientist magazine, contradict conventional wisdom which says that grazing cattle all face in the same direction because they are basking in the sun or huddling together to stay warm.

Berda says the answer was staring cattlemen in the face for 10,000 years - that cattle innately sense which direction is north.

His team scoured satellite images of herds on six continents, identifying more than 8,000 beef and dairy cows. Plotted onto a compass, the animals' orientations were not random. On average, cattle faced no more than five degrees off of geographic north or south.

Live observations of hundreds of deer herds and their snow tracks revealed the same trend, according to the New Scientist report.

Further analysis of cattle showed that in locations where the angle between the geographic and magnetic poles differs most - at extreme latitudes and in places where the geology creates a stronger field - cows line up with the magnetic poles and are further from the geographical poles.

For instance, cows in Oregon, which is relatively far north and subject to a strong magnetic field, face 17.5 degrees off of true north.

"This is a very curious phenomenon," says Wolfgang Wiltschko, of Johann Wolfgang Goethe University in Frankfurt. "It is unclear whether it is in any way related to orientation and navigation."

The unanswered question is "why" - why do cattle need a magnetic sense of direction when they are not migratory animals?

"These are animals that originally lived in dense forests or in grasslands, prairies, savannahs and steppes without landmarks," Burda theorises.

Equally mysterious is how animals zero in on Earth's weak magnetic fields. Some birds have iron crystals in their beaks, and fruit flies seem to use a blue light-detecting protein.

As for cattle, "I have no real idea," he told New Scientist.