Foxes often jump high into the air in order to pounce on prey from above. They have an unusual ability to not only judge the correct direction of attack, but the proper distance to leap in a parabolic arc. How do they do it? Hynek Burda of the University of Duisburg-Essen in Germany speculates that a magnetic spot on their retinas gives them the ability to measure distance:
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.
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