Dogs tear up when reunited with their owners after being separated for a long time, a new study from Japan has found.
The study was published on Monday in peer-reviewed scientific journal Current Biology.
The study’s lead author, Takefumi Kikusui, said in a statement that he and his team “found that dogs shed tears associated with positive emotions.”
Kikusui, who is a professor at Azabu University’s Laboratory of Human-Animal Interaction and Reciprocity in Japan, revealed that when one of his poodles gave birth six years ago, he noticed tears forming in her eyes while she nursed her puppies. He added that the tears dogs produce do not fall down their faces as human tears do.
“That gave me the idea that oxytocin might increase tears,” he said.
Oxytocin, the so-called “love hormone” that plays an important role in a variety of behaviors, including social bonding, has previously been found in both dogs and their human owners during their interactions.
The recent study’s findings suggest that the release of oxytocin strengthens the bond between dogs and their human owners. They also suggest that there is a link between tear production and emotion in animals besides humans.
To see if owner-dog reunions would bring their test subjects to tears, Kikusui and his team separated around 20 dogs from their owners and placed them in day-care centers for around seven hours. The scientists measured the dogs’ tear volumes before and after reunions with their owners and with “familiar non-owners.” They ultimately found that dogs tear up more in the presence of their owners.
The researchers also found that the dogs produced more tears after being given an oxytocin solution, which suggests that the hormone “might mediate tear secretion during owner-dog reunions.”
“Dogs have become a partner of humans, and we can form bonds,” said Kikusui. “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.”
While earlier studies have shown that dogs release oxytocin naturally in the presence of their owners, this is reportedly the first time tear volumes and oxytocin have been studied in relation to owner-dog reunions.
Kikusui and his team plan on studying whether dogs tear up when reunited with other dogs.