A team of Japanese researchers have published a study showing that dogs release more tears when they are reunited with their owners versus other people.
"We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners," said Takefumi Kikusui, one of authors of the study published Monday in the journal Current Biology.
The scientists measured the amount of tears in the dogs' eyes. First, they performed the test on dogs during a normal interaction with their owner.
When dogs saw their owners after five to seven hours of separation, they "significantly" increased tear production in the next five minutes, the researchers found.
They also discovered that the dogs' volume of tears were higher when they reunited with their owner versus other people the dog is familiar with.
According to the researchers, this reaction to tear up is likely linked to the release of oxytocin, nicknamed the "love hormone".
The scientists then sought to test whether the tears might have an emotional impact on the owners. To do so, they asked the owners to rank various photos of their dogs with and without artificial tears by how much they wanted to care for them.
"The dog photos with artificial tears were ranked significantly higher than the normal tearless dog photos," the Japanese research team wrote.
"It is possible that the dogs that show teary eyes during interaction with the owner would be cared for by the owner more," said Kikusui.
