Dogs produce tears when they reunite with their owners, according to a new study out of Japan.
The study, published in Current Biology, is believed to the first of its kind to demonstrate positive emotion stimulating “tear secretion in a non-human animal, and that oxytocin functions in tear secretion”, the researchers from Azabu University said.
The researchers measured the volume of tears produced by 18 dogs upon being reunited with their owners after more than five hours apart, which found that the canines produced more tears when reuniting with their owners than when they are alone.
The increase in tears was not seen when the same test was conducted on 20 dogs who were reunited with familiar humans who were not their owners.
The amount of tears produced by dogs also increased when an oxytocin solution was applied to their eyes, suggesting that the bonding hormone may mediate tear secretion in dog-owner reunions.
Seventy-four participants were then asked to rate a set of 10 photographs showing five dogs – with and without moist eyes – and their level of avoidance or care for the animal.
The study’s co-author, Professor Takefumi Kikusui, said the teary-eyed dogs received 10-15% more people wanting to care for them.
“In humans, infants use tears to transmit negative feelings to their parents, and in response to that the receivers show caregiving behaviour,” the researchers said.
“In this study, we found that a dog’s face with artificial tears can also stimulate caring emotions in humans.”
The researchers said the domestication of dogs have allowed them to gain "high-level communication abilities" with humans through eye contact.
"Through this process, their tears might play a role in eliciting protective behaviour or nurturing behaviour from their owners, resulting in the deepening of mutual relationships and further leading to interspecies bonding."
However, the researchers said the social function of tears through oxytocin is currently unclear.
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