When Dogs Cry Tears of Joy

Japanese researchers have observed a phenomenon that we thought was impossible: a nonhuman animal crying tears of joy. A new study reported in Current Biology this week demonstrated that our canine friends will well up with tears under certain circumstances, and it probably happens more often than we think.

Co-author Takefumi Kikusi got the idea to test dogs for tears a few years ago, after his poodle Jasmine whelped a litter of pups. As an animal behavior researcher at the School of Veterinary Medicine at Azabu University, Kikusi noted Jasmine’s postpartum behavior. “She had teary eyes,” he told the Scientist. “So that gave me the idea that oxytocin might increase tears.”  Oxytocin, he explained, is the maternal hormone which female mammals produce when giving birth and lactating.

Knowing that dogs can also produce oxytocin when interacting with their human mates, Kikusi and colleagues decided to measure doggy-tear levels during that emotional moment when a dog is reunited with its human after a prolonged absence.

They separated pups from their owners for several hours before letting them reunite, waited five to seven minutes into the reunion before measuring the tear-duct output with a standard test. Then they separated dogs from  humans the dogs knew but were not their owners and compared the results, which were unequivocal: dogs produce significantly more tears when reunited with their BFFs.

“We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners,” Kikusi said in a press release. “We were all excited that this would be a world first!”

So dogs apparently weep with joy on occasion; do they also cry when they’re sad? That research hasn’t been done yet but it’s coming (and we don’t want to hear about it). The researchers also plan to measure dog-on-dog interactions to see if those elicit teardrops as well.

Photo credit: Ksenia Raykova / IStock.com