When my dog Raja sees a strange dog, he has a very predictable response. His body tenses, he becomes rigid, and he stands very still, looking at the dog. As a puppy, he was abused by other dogs and even now, years later, he still has trust issues with dogs that he doesn’t know.
However, when he sees a dog he knows, even if a year or more has passed, his tail starts to wag and he confidently goes up to the other dog as they happily start on dog-greeting protocols.
I have often wondered how he recognizes and remembers the dogs he knows. Is it their smell? Is it their general size and shape? Is it the color of their coat?
While all of these factors probably play a role, a new study shows that dogs can recognize the faces of other dogs (Racca, A. et al. 2009. Discrimination of human and dog faces and inversion responses in domestic dogs (Canis familiaris). Animal Cognition, DOI 10.1007/s10071-009-0303-3).
The authors of the study used a technique called Visual Paired Comparison. In this technique, an animal is shown two images projected on screens, one to the right of the animal and the other to the left. Experimenters measure the amount of time that the animal spends looking at each image. If the animal has no preference, she would spend an equal amount of time looking at either image. However, if the animal has a distinct preference for one image over another, she would spend more time looking at that image.
In the dog face study, the experimenters showed 7 adult dogs (1 miniature Dachshund, 2 Lurchers, and 4 mixed-breeds) paired pictures of an unfamiliar dog face and a familiar one.
The dogs spent significantly more time looking at the familiar dog face. This means that dogs not only recognize individual dog faces, but also prefer to look at familiar faces rather than strange ones.
In this respect, dogs are not alone. Increasingly, studies are finding that lots of other animals can recognize individual faces within their own species. So far, this list includes animals as diverse as chimpanzees, monkeys, sheep, cows, budgerigars, and paper wasps.
We humans often like to look at a friendly face. It seems that other animals like to do that too.
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