Behaviour of large mammals in magnetic fields and near power lines

Orientation of cows and deer

In 2008, a paper was published on the orientation of cows and deer.  It used Google Earth aerial photographs and some direct observations to look at whether cows and deer had a preferred orientation, and it suggested that they do in fact both stand and lie down preferentially north-south over other directions.

There are all sorts of factors that could influence which way an animal faces - wind, the slope of the ground, the direction of the sun - but the authors believed they had ruled out these explanations, and the preferred explanation was that the animals could sense the earth's magnetic field and were aligning themselves along it.  We know that some birds and lower species can detect the earth's magnetic field and use it for navigation, but this would be a new discovery if large mammals can do so too.

This first paper triggered various follow-on papers.  A 2009 paper reported that this north-south preference was destroyed near power lines, suggesting that the power-frequency magnetic field of a power line was somehow interfering with the animal's ability to detect the earth's static magnetic field.  A 2011 paper failed to find the effect and gave reasons why the original paper might have been wrong - then the authors of the original paper responded in turn criticising the methods of this more recent paper.  In 2013 paper reported finding the effect again, and that is the most recent piece of work in this area we are aware of.  It would seem that no definitive view on whether this phenomenon is genuine or not has been reached.

Do reindeer avoid power lines and why?

There are quite a few observations suggesting that reindeer avoid power lines.  Any reason for this had always been ellusive.  But in 2014, researchers found that reindeer eyes (along with the eyes of several other large mammals) were sensitive to ultraviolet light, wavelengths that human eyes do not detect because the human lens cuts it out.  Corona - the phenomenon where the electric field on the surface of high-voltage conductors is strong enough to break down air molecules and cause a discharge - produces ultraviolet.  So it is possible that a power line looks to a reindeer (possibly only after dark) like a line of flashing lights, which might be why they avoid them.

The source papers

See the abstracts of all these papers