These tears are caused by oxytocyne, dubbed the “love hormone” by scientists.
Rapid flapping of the tail, jumps in the air and irrepressible licks: every dog owner regularly experiences this joyful reunion with his animal, after a long period of separation.
But to this list of highly demonstrative behaviors there is also a more discreet sign. Dogs also produce tears when reunited with their owners, researchers showed in a study published Monday in the journal Current Biology.
“We had never heard of animals shedding tears in joyful situations, such as reuniting with their owner,” one of the study’s authors, Takefumi Kikusui of Azabu University, said in a statement. Japan, evoking a probable “world first”.
Tears linked to the “love hormone”
The scientists measured the amount of tears produced using a widely used test, the Schirmer test (consisting of a strip placed under the eyelid). They took as a point of comparison a base level raised when the dog was in its usual environment, in the presence of its owner.
After five to seven hours of separation, the amount of tears increased “significantly” within five minutes of the dog’s reunion with its owner. The volume of tears was also higher when the dog was reunited with its master, rather than another person.
According to the researchers, this tear production is linked to the presence of oxytocin, nicknamed the “love hormone”. They also sought to understand what practical role these effusions might play. For this, owners were asked to rank photos of their dog indicating how much they made them want to take care of him.
Tears reserved for humans?
Photos where artificial tears were administered to the animal were ranked “significantly” higher, according to the study.
“It is possible that dogs who show misty eyes during their interactions with their owner lead the latter to take care of them more,” said Takefumi Kikusui.
In humans, infants crying cause parents to pay more attention to them, the study points out. Dogs, domesticated like no other animal, have developed specific communication skills over time. Eye contact has been shown to play a role in forming the relationship between a dog and its handler. The researchers would then like to study whether dogs also produce tears when they find other conspecifics.