Over the years there have been many reports of lost dogs traveling hundreds, or even thousands of miles, to return to their homes. The question that has puzzled scientists has always been "How do the dogs know where they are at, when they have never traveled over this terrain before?", and "How do they know which direction to go in order to get home?" There have been a number of suggestions including some highly speculative notions of an ESP link between dogs and their owners which pulls the animals over many miles. Some other explanations include some kind of ability to read direction based upon noting the constellations of stars at night or a sensitivity to the polarization of light from the sun during the day. Among the many suggested homing mechanisms in dogs, one of the most frequently noted is the possibility that dogs have a magnetic sense. In effect the argument is that dogs can detect the direction of flow of the Earth's magnetic field and thus know where north and south is. Using this internal compass dogs supposedly can navigate with reasonable accuracy over long distances. I have always been skeptical about this possibility but some new data may indicate that I was wrong.
It has been established that certain animals, such as some kinds of fish, and even some mammals like cattle, deer, and foxes, have a certain sensitivity to the Earth's magnetic field. In fish, it is their travel patterns that seem to be biased toward a true north-south course of movement. In mammals magnetic sensitivity shows up most clearly when the animals are resting—thus grazing cattle tend to orient their bodies in a north-south line when they are inactive. In a recent study accepted for publication in the journal Frontiers in Zoology
, a collaborative team of researchers from the Czech University of Life Sciences in Praha, Czechoslovakia and the University of Duisburg-Essen in Essen, Germany headed by Vlastimil Hart decided to see if dogs have a similar magnetic sense.
The idea of checking the body axis of a resting dog doesn't work, since dogs most usually rest in a curled up position with their spines curved. So the researchers looked for a natural behavior where dogs stopped long enough so that their body orientation could be determined, but also an action that would not be affected by any other influences. The behaviors that they chose were the times that dogs stopped to urinate or defecate. Of course to be an accurate indication, the dogs had to be off leash and out in open areas where there are no walls or streets to influence their body orientation.
This was a big study, with data taken from 70 dogs over a period of two years. In total there were 1893 observations during defecation and 5582 observations during urination. Each observer carried a handheld compass and measured the dogs orientation based on the direction of the dog's spine (see the figure). In order to prevent any subtle biases, the people observing the dogs were kept essentially "blind" as to what the experimenters expected, and they had no idea of what kind of influences the experimenters were looking for.
When the experimenters got around to analyzing the data what they found was a big mishmash of nothing, with no selective body orientation coming out of the data. Based on this result they might have walked away with a negative conclusion from their study and concluded that dogs have no magnetic sensitivity. However it was at this point that some members of the team remembered some important features of the Earth's magnetism. The first of these is that the Earth's magnetic axis varies over every 24 hours and it is only a stable indicator of north-south for a limited period of each day. This is because the sun is most intense around midday, and the sunlight causes air particles to ionize (or break up into charged particles) which then affects the electric flow through the atmosphere and this alters the Earth's magnetic field. In addition to the regular daily changes in the Earth's magnetic field there are also irregular disturbances, which are often referred to as magnetic storms. These disturbances are caused by changes in the "solar wind" which is a stream of charged particles continuously emitted by the sun that can also interact with the regular magnetic field of the Earth. So what the researchers did next was to obtain readings from the Geomagnetic Observatory at Munich, Germany. They had to do this for each and every one of the observations of a dog appeared in their data set. Eventually this allowed them to isolate those times when the magnetic field was calm and undisturbed (and pointing along the usual north-south axis). As you might imagine this was a large, tedious, statistical analysis.
Looking at only the data during optimal magnetic conditions they found that the dogs preferred to excrete with their body aligned along the north-south axis. This directional behavior was abolished under unstable conditions in the magnetic field. Thus they were able to conclude that in fact they had the first data showing a magnetic sensitivity in dogs. This means that they could assert that dogs, in effect, have an internal magnetic compass. The existence of such a magnetic sensitivity could help to explain some of the remarkable stories of dogs navigating over long distances in unfamiliar territory in order to get back to their home. Of course a lot of dogs who get lost do not make their way home, despite having such a magnetic sense. Part of the reason for this, appears to be that the magnetic field is only calm for part of the daylight period (due to those ionization effects of the sun in the midday) however there are much longer periods of stability at night. Thus a dog traveling mostly at night is much more likely to have reliable information as to his true direction of movement if he is relying on his magnetic sense.
Stanley Coren is the author of many books including: The Wisdom of Dogs; Do Dogs Dream? Born to Bark; The Modern Dog; Why Do Dogs Have Wet Noses? The Pawprints of History; How Dogs Think; How To Speak Dog; Why We Love the Dogs We Do; What Do Dogs Know? The Intelligence of Dogs; Why Does My Dog Act That Way? Understanding Dogs for Dummies; Sleep Thieves; The Left-hander Syndrome
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