Compass-controlled escape behavior in roe deer

We tested the hypothesis that magnetic alignment, a tendency to align the body axis with a certain angle to the field lines of the geomagnetic field, provides direction indicator (the so-called nonsense orientation) also in mammals. We measured alignment of free-ranging (grazing or standing) roe deer and the compass direction of their escape trajectories as well as the direction from the threat and to the next shelter. Roe deer were significantly nonrandomly aligned along the north-south axis when grazing. In 188 provocations performed in open flat habitats, deer also tended to escape along this axis and avoided to escape westwards or eastwards. Thus, in many provocations (those from east or west), animals fled at wide angles, either northwards or southwards and not straight away from the threat, a strategy that would maximize the distance between the animal and the danger. Since all the factors which might influence direction of escape (sun position, wind direction, direction to the shelter, straight direction from danger) were randomly distributed in time and space, they constitute just statistical noise which does not add. The only common denominator of all data sets was the magnetic field. We conclude that the north-south alignment expresses the readiness to escape along this axis and might help to synchronize the movement and cohesion of the group and also supports mental mapping of space. This is the first study of escape behavior in animals which considers also the role of absolute compass direction. Our findings confirm existence of magnetic alignment and thus magnetosensitivity in the roe deer and provide first evidence for its role as the so-called direction indicator in control of escape behavior in roe deer in particular and in mammals in general. Our results make the speculations more plausible that the magnetic alignment helps to organize and read the mental (cognitive) map of space. (In analogy, humans are more efficient in reading and commenting the map, if it is held in an accustomed direction: with north pointing upwards and if the person aligns with the map and with the visible landmarks.)