Yawn in the presence of your pooch and they're likely to yawn right back at you, a new study shows.
The research, a series of carefully controlled experiments with 25 dogs of different breeds, confirms that dogs are more likely to "catch" their owner's yawns than a stranger's and more likely to respond to real yawns as opposed to fake ones. Fake yawns involve opening and closing the mouth in the movement of a yawn without making any sound.
Researchers also strapped heart rate monitors to the dogs to make sure they weren't yawning because they were stressed or anxious. They weren't.
"We tried to create a comfortable atmosphere in doing the experiment, and sometimes it was so comfortable for them that they fell asleep," said study author Teresa Romero, a research fellow in the department of cognitive and behavioural science at the University of Tokyo.
The study was published online on 7 August in the journal PLoS One.
Although copying a yawn may not sound like such an impressive trick, scientists think it's a sign of something important – the ability to empathise and bond with others.
Measures of empathy
Previous studies have shown, for example, that people who score higher on measures of empathy are more likely to return yawns than people who aren't as empathetic. And the ability to yawn contagiously appears to develop with age.
"Several studies have shown that children don't begin to show contagious yawning until around 4 years of age, and only reach adult levels around 12 years of age," said Elainie Madsen, a comparative psychologist at Lund University in Sweden, who has studied contagious yawning.
In the animal kingdom, contagious yawning appears to be a rare talent. Certain apes, such as chimpanzees and bonobos, which are some of the closest evolutionary relatives to humans, catch each other's yawns. Beyond apes, one species of bird appears to be able to yawn contagiously, and several recent studies have suggested that Canis familiaris, also known as man's best friend, can do it, too.
One thing researchers haven't figured out is why dogs yawn along with humans.
"There are multiple hypotheses, but the empathy hypothesis is the one that has received most attention over the last few years," Madsen said. "I think the evidence in support for it is accumulating."
She said that at a basic level, contagious yawning probably has something to do with group co-ordination and synchronizing group behaviour.
As happened in the new study, Madsen's study of contagious yawning in puppies often lulled the dogs to sleep. She doesn't think that's an accident. "[The dogs] internalized the emotion that yawning reflects, and basically coordinated their behaviour to that of the yawner," she said.
Dogs live in packs, and Madsen expects that all animals that live in groups may demonstrate the ability to catch yawns. However, researchers say the jury is still out on whether cats care that their owners are tired.
"I think it would be very hard to study contagious yawning between humans and cats," Romero said. "They don't pay very much attention to us."
For more insights into animal behaviour, head to the Animal Behavior Clinic at Tufts University.