Lots of organisms, from bacteria to deer, can sense magnetic fields. It's an ability known as magnetoception. Birds and bats use the Earth's field to navigate, and naked mole rats may use it to orient their nests - although why a blind, naked animal that spends its whole life underground cares which way its nest is oriented is a mystery to me.
|Which way should I go?|
It's not particularly surprising that dogs can sense magnetic fields. It may even explain stories of their uncanny ability to find their way home from great distances. What is surprising, to me anyway, is how a group of Czech researchers discovered magnetoception in dogs. After 1,893 observations of dogs defecating, they found a significant preference for pooping along the magnetic field lines. That is, dogs prefer to face toward the magnetic north or south, rather than east or west, when relieving themselves. (Their preferences weren't so clear when it came to urinating, despite 5,582 observations of the dogs in action.)
You might think that the connection is only a correlation, and not causal, but the researchers found that on days when the magnetic field was fluctuating, the dogs' north-south preference disappeared. While on magnetically quiet days, they strongly tended to align north-south.
I've read the paper through a few times, and haven't been able to see any real problems with the analysis. The researchers also did a good job explaining away other factors, like the possibility that dogs don't like to face the sun when temporarily occupied. They even made sure that all the dogs were walked off leash in open fields where the owners and physical structures would not be likely to influence the dogs
One thing I don't entirely buy is the authors' claim that the observers were completely unbiased. They relied on volunteer dog owners to collect the data, and while these people supposedly had no idea what the researchers were looking for, the research group is well known for their investigation of magnetoception in animals. Besides, it doesn't seem that hard to figure out the hypothesis you're testing when someone hands you a compass and asks you to note your dog's pooping posture. I suspect that at least some dog lovers would be inclined to think everything their dog does is special - which might make them less than perfectly objective.
This is clearly an opportunity for someone to take the issue from the realm of mere observation to experiment. All they would need to do is bury some wires in a dog park so that they could control the prevailing magnetic fields, and then see if the animals align themselves in different ways depending on the artificial magnetic field. It shouldn't be that hard to ensure that the whole thing could be set up as a truly double blind experiment.
I suspect we'll never understand is why dogs orient along magnetic fields to do their business. But when it comes down to it, I'm not sure I really want to know.