Foxes zero in on prey via Earth's magnetic field


It sounds like something a guided missile would do. Foxes seem to zero in on prey using Earth's magnetic field. They are the first animal thought to use the field to judge distance rather than just direction.

Hynek Burda of the University of Duisburg-Essen in Essen, Germany, noticed that the foxes he was watching in the Czech Republic almost always jumped on their prey in a north-easterly direction. Given that cows position themselves using Earth's magnetic field, he wondered if something similar was at work.

Foxes jump high into the air before dropping onto prey. Burda's team found that when the foxes could see their prey they jumped from any direction but when prey were hidden, they almost always jumped north-east. Such attacks were successful 72 per cent of the time, compared with 18 per cent of attacks in other directions.

All observers saw the same thing, but Burda remained baffled, until he spoke to John Phillips at Virginia Tech in Blacksburg. Phillips has suggested that animals might use Earth's magnetic field to measure distance.

The pair think a fox hunts best if it can jump the same distance every time. Burda suggests that it sees a ring of "shadow" on its retina that is darkest towards magnetic north, and just like a normal shadow, always appears to be the same distance ahead. The fox moves forward until the shadow lines up with where the prey's sounds are coming from, at which point it is a set distance away.

The idea is "highly speculative but not implausible", says Wolfgang Wiltschko of the University of Frankfurt, Germany.