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Cattle as compasses?

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Compass (Callie Jones)Recent analysis by German scientists of satellite imagery now available on Google Earth, has suggested that ruminants, whether grazing or resting, tend to align themselves along a geomagnetic north-south axis.

A team from the University of Duisberg-Essen examined 308 cattle pastures and plains worldwide, as well as “deer-bed” impressions in the snow created by more than 3,000 deer in over 220 locations in the Czech Republic.

Since the direction of the sun and wind varied widely where the images were taken, it was concluded that the animals must be reacting to the Earth’s magnetic influence, as they pointed to magnetic north.

This conclusion was reinforced by observations of cattle grazing on pasture crossed by overhead power lines. Although these cables emit only a mild electromagnetic field, it is stronger than the background field produced by the Earth, and it was found that the cattle’s north-south alignment was indeed disrupted.

Domestic cattle, being non-migratory, have nothing to gain from orienting themselves according to the Earth’s magnetic field. But it has been suggested that the phenomenon could be a vestige of their evolutionary history, when the survival of their ancestors could have depended on distinguishing the difference between north and south.

The mechanism behind this magnetic phenomenon is still something of a mystery. Studies on migratory birds, fish and insects, as well as some mammals, have demonstrated the presence of cells containing concentrations of magnetite (eg, in the beaks of some migratory birds) which are linked via nerves to cells in the brain. It has been suggested that the cattle may use a parallel mechanism.

Animals that migrate over large distances are thought to use more than one method of navigation. Birds have sharp eyesight and a good visual memory of ground clues but over long distances appear to navigate by sun and stars.

More recent evidence suggests that birds’ eyes include cells containing a protein called cryptochrome, whose reaction to light depends on the surrounding magnetic field. This allows the birds to see the magnetic field, and alter their direction of flight accordingly.

It is thought that there is also an inherited genetic component of a kind of “sky chart” of journeys of previous generations, which enables young animals, such as eels and salmon, to migrate along routes they have previously never encountered.

Whichever, if any, of the above models the magnetic cows fall into, it seems remarkable that farmers have never noticed the phenomenon before.

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