Every dog owner can vouch for how elated their pets are when reunited with them. A new study now shows that dogs may be tearing up, when reunited with their owners.
The study, published in the journal Current Biology on Monday, measured the amount of tears in the dogs’ eyes with the Schirmer Test, which places a specialized strip under the eyelids. Researchers compared the amount of tears in the dogs' eyes during a normal interaction with their owner, as a baseline. This was compared to the amount of tears in their eyes after a separation of five to seven hours.
It showed they "significantly" increased tear production in the first five minutes following reunification with their owners.
"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 from the Azabu University in Japan.
Love hormone responsible for reaction
Oxytocin, or the "love hormone," is responsible for this reaction. It plays a major role in strengthening the bond and building trust between a mother and child, a couple, or any other humans.
Kikusui and his colleagues got the idea for the study after noticing one of his poodles with her puppies. He says he noticed she had tears in her eyes while nursing them. "That gave me the idea that oxytocin could increase the tears,” says Kikusui.
They also noticed that the volume of tears was greater when reunited with their owner compared with other people the dog was familiar with.
The scientists then sought to test whether the tears might have an emotional impact on the owners. 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.
They found that the dog photos with artificial tears were ranked significantly higher than the tearless dog photos.
"It is possible that the dogs that show teary eyes during interaction with the owner would be cared for by the owner more," hypothesized Kikusui.
The authors noted that infants share their negative feelings by crying, which leads to increased care proffered by the parents.
One of the most domesticated animals, dogs have also developed specific communications with humans over time. Eye contact plays a major role in developing the relationship between a dog and its owner.
The researchers said in the future, they would like to study whether dogs produce tears when they meet other canine pals.
