Dogs cry ‘happy tears’ when reunited with their favourite humans
Along with frenzied tail-wagging and plenty of face licks, new research suggests that dogs can even shed tears when they’re happy to see you.
Takefumi Kikusui, a researcher in the school of veterinary medicine at Japan’s Azabu University, first observed the phenomenon six years ago while watching his poodle nurse her puppies, when he noticed there were tears in her eyes.
“That gave me the idea that oxytocin might increase tears,” he said.
Oxytocin is known as the maternal or “love hormone”, Kikusui explained, with previous research finding that the hormone is released in both dogs and their owners when they interact.
To test their teary theory, Kikusui and his colleagues decided to run an experiment where they reunited dogs with their familiar humans, as well as with strangers, and measured the volume of tears in the dogs’ eyes before and after.
Publishing their findings in the journal Current Biology, the scientists found that tear volume increased when the pooches returned to their favourite humans, but not with a person they didn’t know.
In a second experiment, the team added oxytocin to the dogs’ eyes to see whether there was a connection to the tears. With the tear volume also going up after oxytocin was added, they concluded that it was proof that oxytocin plays a role in tear production when dogs interact with their owners.
Surprisingly, when they asked people to rate dog faces with and without tears, people gave more positive responses to photos of teary-eyed pups, suggesting that tear production in dogs also helps them and their owners forge stronger connections.
“We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners, and we were all excited that this would be a world first!” Kikusui said.
Having found that dogs produce tears in situations we’d consider ‘happy’, future work will look to see how teary they get in response to negative emotions and whether being teary plays a social role in how dogs interact with each other.
“Dogs have become a partner of humans, and we can form bonds,” Kikusui said.
“In this process, it is possible that the dogs that show teary eyes during interaction with the owner would be cared for by the owner more.”
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