Talk about animal magnetism, cows seem to have a built-in compass. No bull: Somehow, cattle seem to know how to find north and south, say researchers who studied satellite photos of thousands of cows around the world.

Most cattle that were grazing or resting tended to align their bodies in a north-south direction, a team of German and Czech researchers reports in Tuesday’s issue of Proceedings of the National Academy of Sciences.

And the finding held true regardless of what continent the cattle were on, according to the study led by Hynek Burda and Sabine Begall of the faculty of biology at the University of Duisburg-Essen in Germany.

“The magnetic field of the Earth has to be considered as a factor,” the scientists said.

This challenges scientists to find out why and how these animals align to the magnetic field, Begall said in an interview via e-mail.

“Of course, the question arises whether humans show also such a spontaneous behavior,” she said, adding, what “consequences does it have for their health.”

The study sent Tina Hinchley, who with her husband Duane operates a dairy farm in Cambridge, Wis., to take a new look at an aerial photo taken of their farm a few years ago.

“The cows that were in the pasture were all over the place … about two-thirds were north-south,” Hinchley said.

Two-thirds is close to what the researchers found in their look at 8,510 cattle in 308 pastures. In the study, 60 percent to 70 percent of cattle were oriented north-south, which Begall termed a “highly significant deviation from random distribution.”

Hinchley stressed that one factor that must be considered is cow comfort.

“They don’t like to get hot. Their body temperature is 102, and they are wearing black leather jackets, literally! If turning north-south would keep them cooler, they would stand that way.”

The research team noted that in very windy conditions cattle tend to face the wind, and have been known to seek out the sun on cold days. But they said they were able to discount weather effects in the study by analyzing clues such as the position of the sun based on shadows.

“This is a surprising discovery,” said Kenneth J. Lohmann of the biology department at the University of North Carolina. “Nothing like this has been observed before in cattle or in any large animal.”

However Lohmann, who was not part of the research team, cautioned that “the study is based entirely on correlations. To demonstrate conclusively that cattle have a magnetic sense, some kind of experimental manipulation will eventually be needed.”

Joseph L. Kirschvink of the California Institute of Technology said he wondered if fences around the pastures could affect cattle orientation.

Passive alignment of animals to magnetic fields has been reported in honeybees and termites, he noted. It requires some type of special sensory organ to detect the magnetic field.

“If they have evidence suggesting that mammals are using magnetic fields to orient their movements, this is very cool,” said Mark A. Willis, an associate professor of biomedical sciences at Case Western Reserve University in Cleveland.

Willis, who was not part of the research team, added, “We have only in the last few years begun to understand the mechanisms underlying magnetic field orientation in birds and other smaller animals.”

Indeed, it’s small animals that led to this study, Begall explained. They were researching the magnetic field effect on African mole-rats.

“At one point last year the question came up whether large animals could also sense the Earth’s magnetic field or not. But of course, it is difficult, or maybe impossible, to do these studies in the lab,” she said. “So, the idea arose to look for other large mammals like cattle, and Hynek Burda was fascinated when he recognized that cattle could be found on Google Earth satellite images.”

With satellite images they could tell the north-south orientation of the animals, but not whether an individual cow was facing north or south. You have to get closer to tell which end is which.

Now the researchers are moving on to study sheep, goats, horses, wild boar and some further deer species, Begall added.

The current study said red and roe deer also were found to orient in a north-south direction when grazing and resting, but unlike the worldwide cattle study, the deer portion was limited to the Czech Republic.

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On the Net:

Grazing cattle and sleeping deer tend to align their bodies along the North-South axis of the Earth’s magnetic field, European researchers said on Monday, giving new meaning to the phrase animal magnetism.

Herdsmen and hunters have long known that cattle and sheep tend to face the same direction when grazing, but had believed they were simply positioning themselves according to prevailing winds or the sun’s rays.

Sabine Begall of the University of Duisburg-Essen in Germany and colleagues had a different idea. The researchers studied 8,510 satellite images of cattle and deer herds derived from Google Earth from around the globe, including 308 pastures and plains.

They also looked at deer beds — impressions left in the snow by resting deer — from nearly 3,000 deer in more than 225 locations in the Czech Republic.

They found that whether grazing or resting, these animals face either magnetic North or South. And since the direction of the wind and sun varied widely where the images were taken, the researchers believe the Earth’s magnetic field to be the polarizing factor.

Although not seen before in large mammals, birds, turtles and salmon are known to use the Earth’s magnetic field to guide their migrations, while rodents and one bat species have been found to possess an internal magnetic compass.

The researchers noted that humans and even whales are suspected of having an innate magnetic compass.

Some studies suggest humans who sleep in an East-West position have far shorter rapid eye movement or REM sleep cycles, in which dreams occur, compared with North-South sleepers who got more REM sleep.

“Our results call for an in-depth study of this phenomenon and challenge neuroscientists, biochemists and physicists to study the proximate mechanisms and biological significance of magnetic alignment,” Begall and colleagues wrote in the Proceedings of the National Academy of Sciences.

(Editing by Andrew Stern and Todd Eastham)