Yawning is contagious. When we see another person yawn, we are much more likely to do so ourselves. In humans, this is thought to be a sign of empathy: the more empathetic you are, the more likely you are to catch someone else’s yawn. But what about catching yawns between species? In 2008, scientists at the University of London showed that human yawns are copied not only by other humans, but also by dogs. They concluded that this constitutes scientific evidence for dog empathy.
The researchers tested a group of adult dogs, one by one. Each dog sat with its owner behind it, watching an experimenter that they had not met before. Half the time, the experimenter yawned at the dog; the other half, the experimenter opened and closed their mouth but didn’t yawn. When the experimenter yawned, 21 of the 29 dogs yawned back. But none of them did when the experimenter simply moved their mouth.
More recent evidence has shown that dogs yawn not only when they see a human yawn, but even if they only hear one. This is especially true if they hear their owner yawning instead of a stranger. Another study found that human yawns elicit yawning in puppies, or even make them fall asleep. But this is only true from about 7 months onwards.
In dogs, yawning can be a sign of stress as well as tiredness. Could this explain why dogs catch human yawns? Some people have suggested that dogs might find the sight of a yawning human stressful. To test this idea, researchers at the University of Tokyo yawned at dogs while measuring their heart rates to detect signs of stress. The dogs yawned back, but didn’t show any signs of stress. So if your dog yawns back at you when you’re tired, you’re not stressing it out: it’s empathising with you.