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Dogs cry more when they are happy.
Like humans, dogs produce tears when they’re emotional, and their tears help strengthen the bond between people and their pets, researchers from Azabu University in Japan have found. The study is published in Current Biology.
“We found that dogs shed tears associated with positive emotions,” says Takefumi Kikusui of Azabu University in Japan and one of the paper’s authors.
The findings come from three experiments.
In the first the researchers measured dogs’ tear volume from a baseline and after reuniting with their owners, compared to a person they didn’t know. Their tears increased significantly when reconnecting with a familiar human, but not when meeting the stranger.
Oxytocin, Kikusui says, is known as the maternal or ‘love hormone’. The researchers knew from earlier observations that oxytocin is released in both dogs and their owners during interactions.
Testing the theory that the tears were linked to happiness, the researchers found when they added oxytocin to the dogs’ eyes, their tear volume also went up. That finding supports the idea that the release of oxytocin plays a role in tear production when dogs and their people get back together.
In a third experiment the researchers asked people to rate pictures of dogs’ faces with and without artificial tears in them. People gave more positive responses when they saw dogs with teary eyes, suggesting this plays a role in forging stronger connections between people and their dogs.
Read more: Puppies born ready to communicate with people
The research was prompted after Kikusui’s two standard poodles had puppies six years ago. He noticed when his dog was nursing the puppies, it got teary eyes.
While the study’s findings suggest that dogs cry when they are happy, the researchers say they haven’t tested whether they also produce tears in response to negative emotions, or when they reunite with other dogs.
Watch more: The science behind those irresistible puppy-dog facial expressions
For even more on interspecies friendship, watch Bird’s Eye View on the 2022 SCINEMA International Science Film festival
Watch the 2022 SCINEMA International Science Film festival entry, Bird’s Eye View, by registering to view it for free on the SCINEMA website. Follow the prompts in the email you receive and you’ll find Bird’s Eye View in the Animals playlist. You can watch all the films until August 31 2022 when the festival ends.