Quick tail waving, air jumping and unstoppable licks: every dog owner regularly experiences this joyful reunion with their animal after a long period of separation.
But there is a more discreet sign in this list of highly demonstrative behavior. Dogs also produce tears when reunited with their owners, researchers showed in a study published Monday in the journal Current Biology.
“We have never heard animals shed tears in joyful situations, such as being reunited with their owner,” said one of the study’s authors, Takefumi Kikusui of Azabu University, Japan, prompting a likely “world’s first.”
The scientists measured the amount of tears produced using a widely used test, the Schirmer test (consisting of a strip placed under the eyelid). As a point of comparison, they took the baseline raised when the dog was in its usual environment, in the presence of its owner.
After five to seven hours of separation, the number of tears “significantly” increased within five minutes of the dog’s reunion with his owner.
The volume of tears was also higher when the dog was reunited with its owner rather than another person.
According to researchers, this production of tears is due to the presence of oxytocin, nicknamed the “love hormone.”
They also sought to understand what practical role these outpourings could play. To do this, owners were asked to rank pictures of their dogs by how much they made them want to take care of them.
According to the study, photos in which artificial tears were injected into the animal were rated “significantly” higher.
“Perhaps dogs that show cloudy eyes while interacting with their owner encourage the latter to care more about them,” said Takefumi Kikusui.
Research indicates that in humans, crying babies cause parents to pay more attention to them.
Domesticated like no other animal, dogs have developed certain communication skills over time. Eye contact has been shown to play a role in shaping the relationship between a dog and its handler.
Next, the researchers would like to study whether the dogs produce tears when they find other dogs.