For centuries, farmers have known that their livestock not only gather in large herds but also tend to face the same way when grazing. Experience and folk wisdom offer several possible reasons for this mutual alignment. They stand perpendicularly to the sun's rays in the cool morning to absorb heat through their large flanks, or they stand in the direction of strong winds to avoid being unduly buffeted and chilled.
But cows and sheep don't just line up during chilly spells or high wind. Their motivations for doing so during warm, pleasant and unremarkable weather, or indeed in the dead of night, have been a mystery until now. In a new paper, Sabine Begali from the University of Duisburg-Essen in Germany spied on aligned herds of cows and deer using satellite images from Google Earth.
The images revealed a striking behaviour that had been going unnoticed for millennia, right under the noses of herdsmen and hunters - their herds were lining up in a north-south line like a living compass needle. Influenced by a magnetic sense that has only just become apparent, their default point of reference is not the source of wind or the angle of the sun, but the Earth's magnetic poles.
