Dogs can typically smell and hear far better than their human companions. Now it appears they can sense Earth's magnetic field too, say a team of biologists – and they show it when they poop.
These canine compasses prefer to align themselves along a north-south magnetic axis when they relieve themselves, according to a study in the journal Frontiers in Zoology. The findings may help scientists better understand how that strange sense called magnetoreception manifests in mammals.
Dogs wouldn't be the only animals thought to use magnetoreception: Birds do it, bees do it – and certain types of mammals do it, according to study coauthor Sabine Begall, a biologist at the University of Duisburg-Essen in Germany.
"We discovered [by measuring Google Earth aerial pictures] that cattle align with the magnetic field lines a few years ago," Begall said in an email. "Since then, we studied hunting behavior in [the] red fox and found that they have a preference for N-E during their mousing jumps, and from there it was just a small step to study dogs. First, we looked also at other behaviors but the results were less promising than the 'pooping direction.'"
The scientists studied 70 dogs of 37 different breeds as they defecated (1,893 dumps, to be precise) and urinated (a whopping 5,582 times) – data collected over two years. The researchers found that dogs prefer to point along the north-south axis when they do their business – as long as the magnetic field is stable. When the magnetic field shifts – say, because of an oncoming solar storm – it becomes more difficult to see the pattern, Begall said.
"We were quite frustrated, because we couldn't find a clear preference for a certain direction," Begall said. "Then, we sorted the data according to the prevailing [magnetic-field] conditions at the time of recording, and this analysis revealed a highly significant and predictable effect."
Both male and female dogs took this north-south stance when defecating, the study authors said. But male dogs took slightly different positions when urinating – probably a result of their leg-lifting behavior. How that leg-lifting – right or left? – affects a dog's alignment is "currently under study," the authors wrote.
The authors caution that more research is needed — in part because 'normal' magnetic conditions occurred only in 30% of the cases studied for this work.
If they do indeed sense magnetic fields, why do dogs feel the need to point north-south when they do their business? The authors don't know yet, Begall said.
"It could be that the dogs somehow calibrate their compass or read their 'mental map' during the walks," Begall said. "Imagine that you read a compass during a hike. If the compass needle is shaky, you might dismiss reading the compass at all. That could be the reason why the dogs have no preference when the [magnetic field] is unstable."