New Delhi: We have all seen videos of excited dogs, wagging their tails and jumping to lick their owner’s faces when reuniting with them. Turns out, you are not the only ones happy to see your furry friend after a long day at work, your dog might be teary-eyed too. A new study suggests dogs experience happy tears as well.
A research study, published in the journal Current Biology Monday, has found that dogs tear up when reunited with their owner as a result of release of oxytocin, commonly known as the love or bonding hormone. The study by a group of Japanese scientists suggests that just like human eyes well up at times of joy, the same is the case with dogs – a behaviour that helps strengthen the bond between humans and their canine companions.
While dogs have been known to have tear ducts similar to humans, they have been primarily studied for their physiological functions, to keep eyes clean and healthy. This is perhaps the first study to link tears in dogs to an emotional response, according to the authors of the study.
The authors, Kaori Murata, Miho Nagasawa, Tatsushi Onaka among others, studied 18 dogs using the Schirmer tear test (STT), where a paper strip was placed inside the lower eyelids of dogs to measure how much the strip moistens. Performing the test by separating the dogs from their owners for more than five hours, the researchers measured tear volume released in dogs before and after reuniting with their owner and familiar non-owners. They found that tear volume increased significantly when reunited with their owner but not with a familiar non-owner.
One of the researchers of the study, Takefumi Kikusui decided to study dog tears after watching one of his two poodles get teary eyed.
“I have two standard poodles and I had one female pregnant six years ago,” Takefumi Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University, told the Guardian.
Noticing her face was more tender than usual when nursing her puppies, Kikusui realised her eyes were teary.
“That gave me the idea that oxytocin might increase tears,” he added. “We previously observed that oxytocin is released both in dogs and owners when interacting. So we conducted a reunion experiment.”
Role of oxytocin
The study also found that oxytocin may mediate tear secretion during such owner-dog interactions, based on how the 22 dogs responded to an oxytocin solution applied to the surface of their eyes.
In humans, infants use tears to transmit negative feelings to their parents and elicit caregiving behaviour from the adults. The study found that a dog’s face with “artificial tears can also stimulate caring emotions in humans”.
A group of 74 people, who participated in the study, responded more positively to photos of dogs with artificial tears than those of tearless canines, concluding that emotion-induced tears can influence and strengthen relationships between dogs and humans. The authors emphasised that dogs have been able to use eye contact to communicate with humans, a level of communication unseen in most other animals.
The authors further added, “Through this process, their tears might play a role in eliciting protective or nurturing behaviour from their owners,” noting that it results in “deepening of mutual relationship and further leading to interspecies bonding.”
However, several questions remained unanswered for the team. “We do not yet know if dogs show an increase of tears during a dog-dog reunion. We also do not know how dogs use tears to communicate with each other,” he said. “We need to clarify the social function of dog tears.”
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