If you're ever lost in a remote European forest, you might be able to get your bearings by finding a herd of roe deer. These animals like to align themselves roughly north-south, whether they're standing still or fleeing danger. Roe deer are small, reddish or grayish grazers common in Europe and Asia. Petr Obleser, of the Czech University of Life Sciences in Prague, and his coauthors studied the behavior of these skittish herbivores to look for evidence that they can sense the earth's magnetic field. Two men separately patrolled the Czech countryside for deer. They went on foot, wearing olive-green hunting gear and carrying binoculars. Whenever an observer spotted a roe deer, he stopped and recorded how the deer was oriented: East-west? Northwest-southeast? Then he continued walking toward the animal. When it fled, he recorded the direction it had run in. The researchers were able to gather data on 188 deer. Of these, 115 deer were on their own. The rest were in groups of 2 to 5 animals. How the deer were standing when researchers found them was not random. Deer were most likely to stand along a north-northeast by south-southwest axis. This tendency was stronger when deer were in a group than when they were alone. The time of day, season, wind, position of the sun, or type of habitat didn't affect how the animals were standing. So the researchers concluded that roe deer can likely sense the earth's magnetic field—and line themselves up according to it. As the observers got closer, deer also tended to flee in either a north-northeast or south-southwest direction. If someone was approaching a deer's side rather than its head or tail, this meant the deer might run at an angle instead of straight away from the person. Biologists call a tendency to line up in one seemingly arbitrary direction a "nonsense orientation." Other researchers have seen similar behavior in birds. There's no particular reason that facing roughly north or south should be better than other directions. In fact, sticking to one alignment when running from a predator—rather than just going in the opposite direction of the threat—seems like a bad idea. But Obleser and his coauthors think their magnetic preferences might help roe deer nonetheless. If the deer in a herd (or the birds in a flock) all tend to flee in one direction, it could help the group stay together even when it's in panic mode. There may be some sense, then, to the nonsense.
Image by John Clift (via Flickr)
Obleser, P., Hart, V., Malkemper, E., Begall, S., Holá, M., Painter, M., Červený, J., & Burda, H. (2016). Compass-controlled escape behavior in roe deer Behavioral Ecology and Sociobiology, 70 (8), 1345-1355 DOI: 10.1007/s00265-016-2142-y
