Birds do it, bees do it, even sharks in the seas do it… But can cows detect magnetic fields?
That question is, surprisingly, hotly debated. It all started in 2008 when Sabine Begall and colleagues from Germany and the Czech Republic found, using Google Earth, that cows tend to align themselves north-south along the Earth’s magnetic field (Begall S, Červený J, Neef J, Vojtěch O & Burda H 2008, “Magnetic alignment in grazing and resting cattle and deer”, Proceedings of the National Academy of Sciences, vol. 105, no. 36, pp. 13451-13455, doi:10.1073/pnas.0803650105).
The obvious question to ask is whether the alignment is due to environmental conditions. However, the researchers claimed they could rule this out: the behaviour of cattle under heat stress or when basking in the sun is well known, and not seen in the cows studied; also, the varying local wind patterns didn’t match the orientations (interestingly, although the wisdom accumulated by farmers over thousands of years was sufficient to rule out these environmental causes, no one had ever noticed the north-south alignment before).
For comparison, they also looked at “beds”, or body prints left in snow by red deer and roe deer. These were even more highly correlated along north-south alignment, and being created at night were clearly unrelated to the position of the sun. (Additionally, although the satellite photos of cows weren’t high enough resolution to see the actual direction they’re pointing, i.e. if it’s north or south, the deer beds showed that they face north when resting.)
Perhaps the clincher though is that at high latitudes, where there’s a big difference between magnetic and geographic north, the cows and deer were much more aligned to the magnetic.
So how do they do it? Is it because beef is so high in iron?
Actually, the mechanism that animals use to detect magnetic fields – a skill known as magnetoreception – is still largely unknown. But it has been studied more in some animals than others.
Birds, for instance, are known for their navigational abilities, and they have a few features sensitive to magnetic fields. They have a region in their upper beak that is known to contain magnetite (Fe3O4); also, their eyes use the light-sensitive protein cryptochrome, which is affected by magnetism, so they may be able to “see” magnetic fields.
We might even share this ability: human sinuses have been found to contain magnetite, and the cryptochrome in our eyes is also potentially magneto-sensitive (see Baker RR, Mather JG & Kennaugh JH 1983, “Magnetic bones in human sinuses”, Nature 301, pp. 78-80, doi:10.1038/301078a0 and Foley LE, Gegear RJ & Reppert SM 2011, “Human cryptochrome exhibits light-dependent magnetosensitivity”, Nature Communications 2, doi:10.1038/ncomms1364).
It’s actually with humans that the whole cow compass affair started: Sabine Begall had been studying naked mole rats, which always sleep on the south side of their burrows, and she got to wondering whether sleeping humans also had a preference.
Begall tried using Google Earth to examine campsites to see if there was a pattern, but it turned out to be very hard to see which way people were sleeping in tents. But cows were much more visible, and they indeed showed a pattern.
However, not everyone agrees. In January 2011 another Czech team did their own analysis of satellite photos of cows across Europe, and found no alignment (Hert J, Jelinek L, Pekarek L & Pavlicek A 2011, “No alignment of cattle along geomagnetic field lines found”, Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, vol. 197, no. 6, pp. 677-682, doi:10.1007/s00359-011-0628-7).
But it doesn’t end there. In November, Begall’s team published a response, in which they re-analysed the same photos. They claim that the second study had used a different statistical technique and included a lot of “noise” in their data, including poor quality photos, pastures on slopes and herds near power lines, which supposedly disrupt the magnetic effect (see Begall S, Burda H, Červený J, Gerter O, Neef-Weisse J & Němec P 2011, “Further support for the alignment of cattle along magnetic field lines: reply to Hert et al.” Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, vol. 197, no. 12, pp. 1127-1133, doi:10.1007/s00359-011-0674-1).
So the great magnetic cow controversy rages on. But the original question is still unanswered: what about humans?
This is a topic waiting to be solved, perhaps with better quality satellite photos, or by choosing suitable locations: people lying on beach towels are much easier to see, but the beach is a possible confounding factor.
Or maybe like the deer, we need to examine campgrounds up close, or even just go down to the local park at lunchtime and see which way people are lying. It could be a fun summer research project!