Dogs can shed tears when reuniting with their owners after a prolonged period of separation, a new study, published by a team of Japanese researchers in the Current Biology journal, suggests. Moreover, humans tend to care more about tearful dogs, suggesting that “emotion-elicited tears” play an important role in interspecies bonding and “can facilitate human-dog emotional connections,” according to the study.
The study is based on observations of the behavior of some 20 dogs, as well as a Schirmer tear test performed on the pooches. The canines produced more tears when meeting their owners after five-to-seven hours of separation, while meeting other humans they were familiar with did not evoke the same reaction, the study found.
Canine tear production is linked to oxytocin, the same key hormone involved in social bonding and reproduction in humans, the study suggests. Applying a solution containing oxytocin to the dogs’ eyes increased tear production in a similar way as when they were reunited with their owners.
“In this study, we demonstrated that dogs secrete tears when reuniting with their owner, and our data suggests that this tear secretion is mediated by oxytocin. This is the first report on positive emotion stimulating tear secretion in a non-human animal, and oxytocin functioning in tear secretion,” the study reads.
Unlike any other animal, “dogs have evolved or have been domesticated through communication with humans and have gained high-level communication abilities with humans using eye contact,” the research team suggested. Therefore, canine tears “might play a role in eliciting protective behavior or nurturing behavior from their owners” in a way that’s similar to the bonding between humans and their own children.
People who took part in the research displayed better attitudes towards tearful dogs than their dry-eyed counterparts. The participants were shown pictures of dogs, some of which were treated with artificial tears.
“Human participants rated their impressions on photos of dogs with or without artificial tears and they assigned more positive scores to the photos with artificial tears. These results suggest that emotion-elicited tears can facilitate human–dog emotional connections,” the study said.