There’s a reason you get emotional when watching those dog reunion videos. Dogs do shed tears of joy. That’s according to a study out of Azabu University in Japan which measured tear volume of 22 dogs under different circumstances.
The researchers said that the studied dogs shed “significantly” more tears of joy after getting back together with their owners compared to meeting someone who was not their owner.
They attribute the dogs’ reaction to the release of the “love hormone” oxytocin.
“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,” Azabu University researcher Takefumi Kikusui said in a news release.
Kikusui said he was inspired to undertake the study after observing his poodle, who had puppies six years ago, getting teary-eyed when she nursed them.
Researchers used a Schirmer’s test to measure the dogs’ tear volume. The test works by allowing water in tears to travel along a paper test strip, with the rate of travel being proportional to the rate of tear production.
They measured the dogs’ tears while the dogs were at home. Tear volume also increased when the researchers added oxytocin solution to the dogs’ eyes (not harmful), indicating that hormones play a key role in the tear production.
The researchers also asked people to rate pictures of the faces of dogs with and without teary eyes. People responded more positively to pictures with dogs crying. This suggests that dogs produce tears in situations humans would consider “happy.”
“Through this process, their tears might play a role in eliciting protective behaviour or nurturing behaviour from their owners, resulting in the deepening of mutual relationships and further leading to interspecies bonding,” the study says.
“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.”
Researchers did not test whether dogs produce tears in response to negative emotions or when they reunited with other dogs.
Although the research indicates that dogs react with tears as a xxx adaptive behavior to elicit love from their owners, we here at DogHeirs.com think it also indicates a deeper level of emotional intelligence in dogs that perhaps previously thought.
More on the university’s study can be read at Current Biology.