Animal magnetism

BBC: Cattle shown to align north-south

Images from Google Earth have confirmed that cattle tend to align their bodies in a north-south direction. Wild deer also display this behaviour—a phenomenon that has apparently gone unnoticed by herdsmen and hunters for thousands of years.

In the Proceedings for the National Academy of Sciences, scientists say the Earth's magnetic fields may influence the behaviour of these animals.

This study has Ig Nobel Prize written all over it. It also has several ingredients (animals, Google, unseen forces) which ensured that it received plenty of press coverage. But it is a serious and innovative study with a genuinely interesting result.

For what it's worth, I'm pretty sceptical about the study's reported conclusion that cattle and deer are aligning themselves with the Earth's magnetic field. It is not unreasonable to suggest that such animals—many species of which are migratory—might have evolved some sort of internal magnetic compass, but, off the top of my head, I can think of a number of alternative explanations as to why they might align north-south—or appear to:

• Turning from the prevailing winds: The animals might simply have been facing away from the prevailing winds, which in many parts of the world blow in a (very) roughly north-south direction. In fairness to them, according to the BBC article quoted above, the scientists involved in the study claim to have ruled out this possibility, although no details are given.
• Turning from the sun: It seems reasonable to assume—although this is pure conjecture—that more of the photographs used on Google Earth would have been taken towards the middle of the day, rather than at either end of the day. This would help to avoid long shadows and colour-cast in the photographs, and would mean that the pilots of the aircraft taking the photographs—they are not satellite photographs—would not have to take off or land near sunrise or sunset. In the middle of the day, the sun tends to be in the south in the northern hemisphere and in the north in the southern hemisphere. So, at the time the photographs were taken, the animals might simply have had their bodies turned away from the sun to avoid overheating. Again, the scientists involved in the study claim to have ruled out this possibility. This alternative explanation might, however, also explain why the north-south orientation is less pronounced in Africa, where the midday sun is more overhead, so turning in any one direction would make little difference in terms of the amount of sunlight falling on the body.
• Turning from (or towards) the aircraft: The aircraft which took the Google Earth photographs will have done so by passing back-and-forth along roughly parallel lines to ensure maximum coverage for minimum effort. If, as seems reasonable, their parallel lines were in a north-south or east-west direction, the animals in the photographs might have turned their bodies towards or away from the aircraft as a defence mechanism, to appear either bigger or smaller—who knows what's going on inside a cow's brain?
• Sampling bias: The BBC report says that it sometimes took the scientists hours to find some pictures with good resolution, and that they were unable to distinguish between the head and rear of the cattle, but could tell that the animals tended to face either north or south. Perhaps the scientists simply found it easier to spot north-south facing animals in the photographs. One reason for this might, again, be sun direction. If the sun is in the south, say, and a cow faces north-south, the roughly rectangular shape of the animal's body when viewed from overhead will be extended by the animal's north-pointing shadow. But, if the cow is facing east-west, the shadow will make the cow's overhead image appear to be more 'square-shaped' (i.e. less like a cow). East-west-facing cows might simply be harder to spot!

I am not saying that any of my alternative explanations for why these animals appear to be aligned north-south is correct; I am merely saying that I don't know whether the study adequately deals with such alternative explanations. If only the report weren't locked away behind a publisher's paywall, we might all be able to come to our own conclusions.