THEY could well be the world鈥檚 smelliest magnets. Grazing cows tend to align north-south, according to a new study of 308 herds based on satellite photos from Google Earth.
The animals鈥� orientation suggests that, like migratory birds, sea turtles and monarch butterflies, they can sense the Earth鈥檚 magnetic field, says Hynek Burda, a biologist at the University of Duisburg-Essen in Germany.
Even rookie cowboys know that cattle in a herd tend to align themselves in the same general direction. Some researchers have argued that the animals are basking in the sun, avoiding wind, or huddling together to stay warm. Yet in the 10,000 years since humans domesticated cattle, their geomagnetic sensitivity has gone unnoticed, or at least unrecorded, Burda says.
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His team scoured satellite images of herds on six continents, identifying more than 8000 beef and dairy cows, and found that the cows鈥� orientations weren鈥檛 random. The average size of each one鈥檚 deviation from north-south was just five degrees. Field observations of hundreds of deer herds and their tracks revealed the same trend (Proceedings of the National Academy of Sciences, ).
Further analysis of cattle showed that in locations where the angle between geographic and magnetic poles differs most, such as extreme latitudes, and in places where geology creates a stronger field, cows orient more in line with magnetic poles rather than the geographic poles. For instance, cows in Oregon, which is about 44 degrees north and subject to a relatively strong field, face 17.5 degrees off true north towards magnetic north.
鈥淭his is a very curious phenomenon,鈥� says Wolfgang Wiltschko of the University of Frankfurt, Germany. 鈥淚t is unclear whether it is in any way related to orientation and navigation.鈥�
So why might an animal known for its languor need an internal compass? A clue may lie in their ancestral habitat. 鈥淭hese are animals which originally lived in dense forests or in grasslands, prairies, savannahs and steppes without landmarks,鈥� says Burda.
