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The research team looked for fields all over the world where magnetic north was to varying degrees either west or east of geographic north.
Grazing animals are known to orient themselves to minimize heat loss by wind or maximize their exposure to sunlight.
But the universality of grazing positions across the globe—and across various climate conditions—was not diluted by either of these factors, the study authors found.
The researchers conclude that the Earth's magnetic field is the common factor that could somehow be influencing the animals.
"[W]e were surprised to have such a wonderful tool like Google Earth, for free, and that no one has ever used it for biological studies in general, and especially not in orientation studies," Begall said.
To further test their results, the team assigned university students to analyze the same Google Earth images, and the students turned up the same result: Cows are grazing in positions that align with Earth's magnetic field.
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Wolfgang Wiltschko, an ornithologist with the J. W. Goethe University in Frankfurt, Germany, called the alignment "a very curious phenomenon."
Wiltschko, a leading expert of magnetic orientation in animals who was not involved in the new paper, said the study conclusion "appears to be quite clear-cut from the data."
He noted that it remains unclear whether the cows' alignment with Earth's magnetism is related to orientation and navigation in other species.
He said termites align their mounds with magnetic lines in Australia, where it might help to coordinate building activities and serve as air conditioning.
In many other cases of non-migrating animals apparently responding to Earth's magnetism, though, "nobody knows so far what advantage this might have for the respective animal," he said.
Begall and her co-authors also note it's unclear why cows and deer would align themselves with Earth's magnetism. But it could have management implications, she suggests.
"If we assume that our findings are real, we could ask what consequences does [barn] housing in east-west orientation have," she said.
"Does it influence the animals' physiology, as in milk production?"
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