They could be the world's smelliest magnets. Grazing cows tend to face the North and South Poles, claims a new study of 308 herds made using Google Earth satellite photos.
The ungulate's 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.
Even the greenest of cowboys knows that cattle in a herd tend to align themselves in the same general direction, and researchers have argued that's because the animals are basking in the sun or clumping together to stay warm. Yet in the 10,000 years since humans domesticated cattle, their geomagnetic orientation has gone unnoticed, or at least unrecorded, Berda says.
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 weren't random. On average, cows faced five degrees off of geographic north or south. Live observations of hundreds of deer herds and their snow tracks revealed the same trend.
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 thegeographical 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."
Why might an animal known for languor need an internal compass? "These are animals that originally lived in dense forests or in grasslands, prairies, savannahs and steppes without landmarks," Burda says. 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 cows, "I have no real idea," he says.
Journal reference: PNAS (DOI: 10.1073/pnas.0803650105)
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