When the four-legged friends stop during a walk to defecate or urinate, they tend to do so along a north-south axis, provided the earth's magnetic field is stable at the time, the scientists said on Friday.
There was no notable difference in magneto-sensitivity among breeds, which ranged from a tiny Yorkshire terrier to a large St Bernard, said team member Dr Sabine Begall of Germany's Duisburg-Essen University.
"We found that the dogs are wonderfully aligned north-to-south – somewhat more so when they defecate than when they urinate — but only when the magnetic field is stable," Begall told AFP.
For the study, published in the journal Frontiers in Zoology, the 10-member Czech and German research team asked 37 dog owners equipped with compasses over two years to record which way their total of 70 furry friends faced when they relieve themselves.
Initially, the scientists crunched the data from over 7,000 such events but found no clear trend. However, when they looked only at times of low magnetoelectric fluctuation, "there was a wonderful correlation", said Begall.
The findings are another clue that animals can sense electromagnetic waves not noticed by humans, and that dogs, aside from their sharp senses of hearing and smell, also have a "magnetic sense".
In 2008 the team studied Google Earth images and found that cattle tend to graze and lie down along a north-south axis, pointing to a sensitivity also suspected in migratory birds and other species.
"There are anecdotal reports that dogs find their way home over hundreds of kilometers (miles), and an explanation may be that they use the Earth's magnetic field for their orientation," Begall said.
What exactly is going on inside a dog's head when it poops is however "pure speculation" for now, said Begall.
It may be that dogs take stock of where they are, the same way a hiker will orient a map northward, and that they can't do this when high electromagnetic activity makes their "compass needle vibrate".
On the other hand, she said, it is possible that, when dogs feeling the urge to relieve themselves and sense a stable and comforting north-south polarity, "they are especially relaxed".