Why Deer Avoid Running East or West When Threatened

June 8, 2016 | Erica Tennenhouse

Blacktoft deer running
Photo credit: Jonathan Kershaw/flickr (CC BY 2.0)

Inner compass helps roe deer plan their escape.

The instinctual response of a startled deer is to run. But which way?

Researchers posed that very question, and got a very specific answer: startled deer run either north or south.

For their study, which was published in the journal Behavioral Ecology and Sociobiology, observers repeatedly approached unsuspecting wild roe deer while they were grazing. Once the observer got close enough to startle a deer, it would inevitably bolt, and the direction in which the deer ran was recorded.

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The getaway almost always followed the north-south compass axis, with the deer seemingly avoiding eastward or westward movements. Senior author Hynek Burda from the University of Duisburg-Essen in Germany explained to The Science Explorer, “If you approach the roe deer from south, it will most probably escape northwards; if you approach it from the north, it will most probably escape southward; and if you approach it from either east- or westward, it will most probably escape either north- or southward.”

Thus, in many cases, the deer fled at wide angles rather than running straight away from the threat — a strategy that would maximize the distance between the animal and the danger.

The north-south preference was more pronounced in groups than in single animals, suggesting that this behavior might help to coordinate group movement. For herd animals like deer, there is safety in numbers, so it is in the best interest of the deer to have a pre-planned escape route that maintains group cohesion.

The tendency of the roe deer to escape along a particular compass axis indicates that they are sensitive to magnetic fields, something that the researchers have long suspected. “Already previously we observed that roe deer tend (…) to stand, graze, and rest aligned along the north-south axis and that this alignment is not obvious under high voltage power lines where the magnetic field is disturbed,” said Burda.

Regularly aligning their bodies in a north-south orientation might help the roe deer to better comprehend their mental maps of the landscape. Burda offers the analogy that humans find it easier to read a paper map if it is held in a particular direction, with north pointing upwards.

Other animals, like homing pigeons and sea turtles, are also capable of sensing magnetic fields, but how they do it is still unknown. Likewise, the mechanism by which roe deer register the magnetic fields around them has not yet been determined, according to Burda.

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