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Foxes use Earth’s magnetic field to jump on prey

Foxes are the first animals thought to use Earth’s magnetic field to judge distance, not just direction.

Birds do it. Bees do it. Now, foxes are the most recent of Earth’s animals suspected of utilizing Earth’s magnetic field as part of their everyday functioning.

Foxes that are hunting small animals in high grass or deep snow might be using the magnetic field to launch a successful attack against prey. Writing in the journal Biology Letters, a Czech research team said it suspects the foxes use an internal compass to judge both direction and distance.

It’s been shown that cows and deer, not just birds and bees, orient their direction to the Earth’s magnetic field. But foxes are the first animals thought to use an internal compass to determine the distance to prey.

Foxes jump high to surprise their prey from above, a hunting technique called “mousing.”  Czech researchers observed that foxes on the hunt tend to direct their jumps in a roughly northeastern compass direction, regardless of the time of day, cloud cover, or other factors that could affect how they perceive their prey. In fact, a large majority of the nearly 600 attacks the scientists observed were oriented in the same direction. They found that 74 percent of the north-east-oriented attacks were successful, while attacks launched in other directions had only an 18 percent rate of success. That’s too big a difference to be random, the scientists believe.

Foxes are known to use their keen sense of hearing before launching their jump, and that works well when they can also see their prey. But the scientists had reason to suspect that they had another sense to judge how far to jump when they can’t see small creatures in snow or high vegetation.

The research team wrote:

We suggest that mousing red foxes may use the magnetic field as a ‘range finder’ or targeting system to measure distance to its prey and thus increase the accuracy of predatory attacks.

They suggest that the fox may see a ring of “shadow” on its retina, that is superimposed on its surroundings and always fixed towards magnetic north. The fox would line up the shadow with where it hears its prey, and is thus always at a fixed distance away from the prey when it launches its attack.

Here’s how Nature explains it:

Think of a laser pointer attached to you that always points slightly downwards in the same direction. Now think of some object on the ground. If you walk towards the object until the laser spot is on top of it you know that object is a set distance away.

That may explain why foxes are such good hunters: they use the Earth’s magnetic field to zero in on their prey.

Klaus Schulten on how birds navigate

Lindsay Patterson

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