Ungulate magnetoreception

Last year, an article appeared in the Proceedings of the National Academy of Sciences of the United States of America suggesting that cattle and deer grazing and at rest are ubiquitously oriented North-South. The initial tip-off came from researchers analyzing Satellite images from Google Earth. Further findings suggest that low-level magnetic field emissions from the likes of power lines show a disruption in cattle herd orientation. While the methods are inconclusive, the findings warrant further research. Though it does not follow that these animals have a sense of magnetoreception (they could merely be exposing their elongated sides to the warmth of the East-West "traveling" Sun), it is an intriguing notion. Of course it wouldn't be too far fetched considering we have the sensory percept apparatuses to detect electromagnetic radiation in the visible spectrum. However, we have evolved such a mechanism due to its pertinence to our well-being. Being a motile creature, it is useful to navigate the world we live in. Stationary organisms like a sea sponge have no use for eyes; natural selection would not favor the evolution of such a sense organ. So then, a logical question to ask: for what reason might ungulates develop a sensory mechanism by which they detect magnetic fields? Further, what might this mechanism be? I cannot think of any (scientifically acredited) sensory perceptual mechanism that is not manifested anatomically. This leads me to think that either magnetoreception capabilities are in stark contrast to the evolutionary model we have all come to know, certain organs have eluded verterinary sciences, or geomagnetic fields affect certain known sensory mechanisms in a manner we do not yet understand.