It’s easy to be amazed at what a dog can smell—Covid-19, cancer, fear, time, their owner’s odor—but at least olfaction is a sense we understand. However weak our human sense of smell may be in comparison to our dog’s, we still have the ability to use our noses to detect chemical odors.
The idea of being able to sense the Earth’s magnetic field is almost as incredible to me as the ability of Haley Joel Osment’s character in the movie The Sixth Sense to see dead people. I just can’t relate to it. Yet, dogs are not the only animals with this ability. Birds, whales, dolphins, turtles, honeybees and mole rats are among the animals who share this widespread trait.
A 2013 study found that dogs preferred to eliminate with their bodies aligned along the north-south axis of the Earth’s magnetic field. While it’s not clear why they do this, the study suggests that dogs can sense the magnetic field and that their behavior is influenced by it. A few years later, in 2016, a study was published that may explain how dogs are able to sense that field. Researchers found that canine eyes contain cryptochrome 1, a light-sensitive molecule that reacts to the magnetic field when it is simultaneously stimulated by light.
This molecule plays a role in the navigational abilities of birds, allowing them to sense the magnetic field through activation of the visual system. (Birds also detect the magnetic field through cellular-level ferrous particles, called magnetite, as do mole rats, who live underground.) In mammals, cryptochrome 1 has been found in only two of the 18 orders of mammals—carnivores (including canines but excluding felines) and primates (including orangutans).
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Now, in 2020, another piece of research reveals a way that being able to sense the Earth’s magnetic field influences dogs’ behavior. In this study, the researchers chose to focus on hunting dogs because they are generally considered to have amazing homing abilities. They outfitted 27 hunting dogs of 10 breeds with GPS trackers and collected data from a total of 622 daylight excursions in 62 locations. The dogs’ trips lasted 30 to 90 minutes and were undertaken in forested areas away from buildings, power lines and roads. The paths they took out and back were the subject of the study.
Many dogs followed their own scent back to the starting point using a method called “tracking,” which was observed in 399 returns. But in 233 excursions, dogs came back to the starting point via a novel route, a process called “scouting.” In 50 cases, dogs combined both strategies in a single return route.
A majority of the dogs who returned by scouting began with a short run (about 20 meters/65 feet) along the Earth’s north-south axis; they did this no matter what direction they needed to go in order to return to the starting point. The researchers hypothesized that the dogs perform this initial “compass run” to get their bearings.
Though scouting dogs’ routes were far more likely to begin along a north-south axis, for tracking dogs, the direction of the start of the return route was random. Another difference was that the scouting dogs returned to their owners faster than the tracking dogs. Gender and breed did not influence the likelihood of employing a scouting versus a tracking strategy, nor did wind or sun.
Activity along the north-south alignment of the compass axis is observed in many animals. Such behavior allows animals to access a universal reference frame that is so useful for navigation. Despite dogs showing some of the same abilities and mechanisms as migrating birds, marine mammals and sea turtles, there is still so much more to explore about dog homing abilities. What we do know so far is that they have their own internal compasses, just as people have been saying for ages.