Farmers, hunters, biologists and holiday-makers have invested much time and speculation on observations of cows and deer. Farmers identify that cattle face into the wind, whereas sheep face away. Hunters are very aware of wind direction while stalking, and will try to approach from down wind. Biologists have discussed body alignment strategies to make use of, or avoid, solar heating. And I remember my holidays being littered with sayings such as `The cows are lying down – it must be about to rain... now the cows are standing up – it must be about to rain...'
It was therefore a bit of a surprise when Sabin Begall from the University of Duisberg-Essen, Germany, and her colleagues from the Czech Republic reported that Google Maps show a previously undescribed tendency in cattle:they align their bodies predominantly north–south (or, as the head is not easily distinguishable in the satellite images, perhaps south–north). It is such a surprise, in fact, that other explanations– confounding factors such as wind or sun direction – immediately spring to mind. But, when the best possible account is taken of these by considering prevalent wind directions across the world and measuring sun direction from shadows, they don't explain the observed north–south alignment bias.
Might sampling with Google Maps somehow provide a bias? It is difficult to see how, but more down to Earth measurements confirm this north–south alignment tendency. Both grazing deer and their `beds' – body prints of resting deer in the snow – tended to have the head-end pointing north. But, presumably because of predation risks from lynx, approximately one-third of the deer faced south. Anecdotally, this preference for facing north sounds quite extreme: when looking around, the deer kept their bodies pointing north,and changed their body direction for short periods when moving to the new grazing sites.
That the mechanism underlying this directional bias is magnetic is suggested from the Google Maps data: in regions where there is a big difference between magnetic north and true north (i.e. the axis of Earth rotation), cattle were much better aligned to magnetic north.
Interestingly, though, direct (magnetic) north/south is not the mean for cattle, falling outside the 99% confidence intervals in 3 of the 6 continents measured. In Africa and South America, cattle align more than 30 deg. east;worldwide, cattle actually orientate themselves NNNNE–SSSSW.
So, Begall and colleagues have made a fascinating observation, and gone to some lengths to discount confounding factors, justifiably claiming that the`most parsimonious' account for body axis direction is magnetic alignment.
And, with this, they `challenge neuroscientists and biophysics to explain the proximate mechanism'. I would argue that perhaps a greater challenge is to behavioural and evolutionary biologists to determine the ultimate cause of this behaviour. Why on Earth should cattle and deer favour aligning with magnetic north–south? And why, in some regions, NNE/SSW?