The research team that discovered magnetic cows – visible from space, no less – has now determined that foxes also appear to possess an internal compass. Vulpes vulpes may even be using their ‘magneto-reception’ as a rangefinder to assist their hunting.
Foxes often utilise a hunting behaviour known as ‘mousing’, where a high jump takes the animal above small prey such as voles, which are doubtless surprised to find the relatively large predator descending on them from out of the sky.
Now Hynek Burda of the University of Duisburg-Essen in Germany and his team show that foxes tend to jump in a north-eastern compass direction. In addition, successful attacks are “tightly clustered” to the north, they report in Biology Letters.
‘Magneto-reception’ has previously been documented in insects, birds and some mammals, but Burda’s team sparked huge interest in 2008 when they reported that cows and deer should be added to the recepting-ranks as they tend to align north-south. They later showed that ‘B-field bovines’ failed to exhibit the same north-south preference when they grazed near field-disrupting power lines.
Their latest discovery came about when Jaroslav Červeny, an author on the magnetic-cow study, noticed a fox mousing in a northward direction. With his curiosity piqued, the hunt was on and some 592 mousing jumps by 84 foxes were observed and analysed.
When hunting in low-cover – where prey would be spotted visually – there was no real preference in jumping direction. But in high vegetation or snow there was a significant preference for north-eastern jumps. And in cover 74% of successful attacks clustered around 20 degrees clockwise of magnetic North, with 15% due south and most other directions yielding no dinner for the fox.
The association also appeared unrelated to factors that you might expect to influence the direction a predator approached a tasty victim – such as wind direction and the position of the Sun. In addition, in high cover or snow there is no possibility for shadows cast by foxes to be a factor, notes Burda.
Once they had convinced themselves that foxes did align, says Burda, the question became why.
“Our favourite hypothesis,” he says, “is that the magneto-reception can be used as a rangefinder to measure distance.”
A similar idea is expressed in a recent paper by Virginia Tech’s John Phillips in the Journal of Experimental Biology. Phillips posits that a magnetic compass may in some animals help “interface metrics of distance, direction and spatial position”.
As Burda explains it, the idea is that a fox may perceive the magnetic north direction as a dark or light patch in its vision. Aligning a spot where prey is likely to be with this spot will mean it is always the same jump distance away, at least for a non-migratory species that always experiences the same inclination of the magnetic field (see explanatory image below).
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.
Having found it in cows, deer and now foxes, Burda says, “I can imagine this magnetic sense is in many animals.”
Image top: mousing fox photo by Jaroslav Vogeltanz.
Range finder graphic: Hynek Burda.