October 25, 2021

I, Science

The science magazine of Imperial College

Dogs prefer to align themselves in the north-south axis when pooing, so are thought to detect geomagnetic field lines ...


All dog-owners are well acquainted with the agonising process that their pet goes through each time nature calls. It begins as they veer off course, no longer merrily trotting at your heel, but gripped by a silent, invisible force steering them astray. Nose to ground they track, back and forth, back and forth, back…is this the spot? No…onwards then, back and forth. Until! Finally! Yes, they have it, the perfect patch, now simply to circle a few times, a little shift, a small wiggle, a final readjustment – and the deed is done. All that, just for a number two!

Now, I’ve always believed that this excessive pre-toilet rigmarole is based on a primitive survival instinct – something to do with picking the patch most protected from predators. But a 2013 study led by Vlastimil Hart, published in Frontiers in Zoology, blows my theory out of the water. By measuring the direction of the body axis of 70 dogs each time they defecated over a 2 year period, the team found that our canine companions are in fact carefully aligning themselves along the north-south axis.
It would be prudent to question why on earth a team of scientists should decide to measure any dog’s pooping-direction, let alone 70 of them and turn it into a study. In truth, the scientists didn’t set out to study their toilet habits; rather, they were on a mission to find out more about the mysterious sense of magnetosensitivity.

Magnetoreception is the process by which animals are able to sense the geomagnetic fields of the earth. And scientists don’t know a great deal about it. What we do know is that the earth is one giant magnet, with its magnetic poles roughly equivalent to the geographical North and South poles. Magnetic field lines emanate from the southern magnetic pole, run up and around the earth, and re-enter at its northern equivalent. These lines vary in magnetic intensity, running at a gradient lowest at the magnetic equator, and peaking at either pole. Certain animals can sense these magnetic field lines, extract information about their vector and/or intensity, and use it to build a navigational map of sorts.

However, scientists are still puzzling over exactly which animals possess this sense, how it works and what all of its possible functions are. Many animals are thought to be magnetoreceptive – the most highly documented of which are migratory birds, famed for their geomagnetically-guided, winter navigation to warmer, southern climes. However, magnetosensitive characteristics have also been scientifically observed in a plethora of other species, ranging from hatchling leatherhead turtles scrabbling to find their way to sea, through to nesting Zambian mole rats. In fact, some degree of magnetoreceptive capacity has been observed in molluscs, arthropods and all major groups of vertebrates. There is even some speculation over the existence of a subconscious geomagnetic sensitivity in humans.

However, for all of its ubiquity, the mechanisms underlying magnetoreception are still shrouded in mystery. Three major models have been proposed. The first, induction, is based on the idea that as fish swim in different directions, they cross geomagnetic field lines, which can then be detected by their electric organ. However, this theory is restricted to marine mammals only, since it requires highly conductive salt water as a surrounding medium. The second model is called the ‘radical pair’ theory. The basic idea is that specialised photopigments act as a ‘chemical compass’ depending upon their alignment with the geomagnetic field. This mechanism is thought to be viable in birds, amphibians and sea turtles. The third hypothesis suggests that tiny crystals of magnetite are crucial geomagnetic sensors. This has been supported by a study led by Freire in 2010, showing that beak-trimmed chickens, which lack the magnetite-dense tip of non-trimmed birds, also lose their magnetoreceptive abilities.

Given how little is known about the reception of the magnetic field, knowledge of the neural pathways facilitating the processing of such magnetic information is even murkier. The vast majority of evidence is derived from bird studies, and tentatively indicates that magnetic data is processed by parts of the visual system. However, since the competing theories of reception vary between species, it would be unwise to extrapolate these findings across all species and types of magnetosensitivity.

Scientists want to find out more about magnetoreception, and this is where our pooping dogs re-enter the story. Dogs seem likely possessors of such a sense. After all, strong evidence suggests that their evolutionary cousin, the red fox, is magnetosensitively equipped, whilst the exceptional homing abilities of dogs and wolves points towards an ability to detect some guiding navigational stimulus. As such, the aim of the toilet study of Hart et al was to observe whether dogs are indeed magnetosensitive. They did this by observing spontaneous alignment of dogs during a range of diverse activities such as feeding and resting. They eventually settled on defecation as the single best indicator of alignment, due to its frequency, ease of classification and relative resistance to changes in surrounding. What they found was that under calm magnetic conditions, dogs preferred to align themselves along the north-south axis whilst defecating. However, if the magnetic field was disrupted, this behavioural pattern was abolished. This is a strong indication that dogs are indeed magnetoreceptive.

Further research is required to establish whether dogs really can detect the geomagnetic field lines, but this study offers positive early indications that they do. If dogs are indeed magnetosensitive, this would open up a new realm of magnetobiological research, given how widely available and easily trained they are as experimental subjects. Furthermore, given the prevalence of canines as experimental animals in biomedical and behavioural research, the discovery of a new sense could have important influences on the design of such studies and the conclusions drawn from them.

There is still much to be discovered about magnetobiology, but this latest finding will help to point scientists in the right direction towards uncovering the mechanisms of this intriguing phenomenon. For now though, we can thank Hart et al for providing us with a delightful nugget of knowledge, happily combining scientific progress, fluffy dogs and a healthy dose of puerile humour.