If you’ve ever given a dog a boop on the snout, you may have noticed that its rhinarium—the furless patch of skin that surrounds the nostrils—is wet and cool. A new study published in Scientific Reports has found that these chilly rhinaria make dogs sensitive to radiating heat, which in turn might help them track down warm-blooded prey.
Dog noses are chock full of nerve endings—they have more than 100 million sensory receptor sites in their nasal cavities, compared to humans’ six million—making them extraordinarily keen sniffers. It thus seemed likely, according to the study authors, that dogs’ rhinaria serve some sort of sensory function.
Low tissue temperature seems to compromise sensory sensitivity in animals with one notable exception: crotaline snakes, also known as pit vipers, which seem to strike more accurately at warm-blooded prey when their heat-sensitive pit organs—located between each eye and nostril—are colder. Cool snakes are also more sensitive to thermal radiation. Perhaps, the researchers theorized, pooches deploy their noses for heat detection, too.
To test the theory, the researchers trained three pet dogs to choose the warmer of two panels. One, according to Gizmodo’s George Dvorsky, was heated to between 51 and 58 degrees Fahrenheit higher than the ambient temperature, similar to the body temperature of a fur-covered mammal. The other, which served as the control, had a “neutral” temperature close to that of the ambient environment. After the training, the dogs were put to the test in a double-blind experiment; neither they nor the people carrying out the trial knew from the get-go which object was warmer, since nothing visually distinguished them.
Still, all three dogs were able to home in on the warmer object, suggesting that they can detect even weak thermal radiation. “[T]he temperature of the mammalian bodies that emit [thermal radiation is not very high, unlike the Sun for instance,” first study author Anna Bálint, a biologist at Lund University in Sweden, tells Gizmodo. To pick up on the heat radiating from warm-blooded prey, dogs would need “very sensitive sensors.”
The nose seemed like the most likely candidate leading the dogs in the right direction. All other parts of a dog’s body are covered in insulating fur, with the exception of the eyes, which “are not suitable for receiving infrared radiation, because the sensitive structures are hidden behind a thick layer of tissue,” study co-author Ronald Kröger, also a Lund University biologist, tells Gizmodo. But to test their theory once again, the researchers conducted functional MRI scans of the brains of 13 pet dogs. The left somatosensory cortex in dogs’ brains—which “delivers input from the nose,” according to Virginia Morell of Science—was more responsive to objects emitting weak thermal radiation than neutral objects.
The researchers don’t know precisely how dog rhinaria convert energy into a nervous signal, and it’s not clear whether pups’ heat-detecting abilities are particularly effective if their hypothetical prey is far away. The test objects were placed around five feet from the dogs; Gary Settles, a mechanical engineer at Pennsylvania State University who was not involved in the study, tells Science that he doubts “dog rhinarium can distinguish patterns of hot and cold objects at a distance.”
But for shorter distances, at least, being able to sense the heat emanating from prey could help canines hunt even if their sight, smell or hearing is obscured. That may not matter much to domestic dogs, but their closest wild relative, the grey wolf, preys on large, warm-blooded animals. “[T]he ability to detect the radiation from warm bodies would be advantageous for such predators,” the authors note in the study. And perhaps most importantly, the study offers yet another reason as to why your dog is great: Its nose knows more than you might think.