Canine crying controversy: When dogs cry, scientists differ

25 Aug 2022

Image: Madoka Nakamura

A recent study found that dogs shed tears associated with positive emotions, but some scientists aren’t so sure canines cry because they’re happy.

A study on dog behaviour found that our canine companions cry more when they are reunited with their human owners.

The study hit headlines everywhere when it was published in the Current Biology journal earlier this week on 22 August. The interest is testament to how much we adore our furry friends.

One of the study’s lead authors, Takefumi Kikusui of Azabu University in Japan, explained that he and his colleagues began looking into the things that sparked sobbing in dogs a few years ago.

The scientist, who owns poodles, noticed that tears began appearing on his dog’s face when she was nursing her puppies. This led him to wonder whether oxytocin was a factor in the sudden appearance of tears in his pet’s eyes. Oxytocin is known as the love hormone and human mothers often have increased levels when they are caring for their babies.

The researchers knew from earlier observations that oxytocin is released in both dogs and their owners during interactions. Based on this, they decided to run a reunification experiment and see if it brought dogs to tears.

First, they used a standard test to measure dogs’ tear volume before and after reuniting with their owners. They found that dogs’ tears increased when they were reunited with the familiar human.

When the researchers added oxytocin to the dogs’ eyes, their tear volume also went up. That finding supports the idea that the release of oxytocin plays a role in tear production when dogs and their owners get back together.

The researchers then turned their attention to the owners. They asked people to rate pictures of dogs faces with and without artificial tears in them. People gave more positive responses when they saw dogs with teary eyes. These findings suggest that dogs’ tear production helps to forge stronger connections between people and their dogs.

Kikusui said that the findings came as a surprise. “We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners, and we were all excited that this would be a world first.”

However, not all dog behavioural scientists were as convinced by the research findings. “If we accept the evidence of this paper, this is one of the most stunning discoveries in animal expression of emotions of all time,” Clive Wynne, a canine behaviour specialist at Arizona State University, told The New York Times. But, he added, “it would take a lot to convince me”.

Another scientist, Lauren M Bylsma, a clinical psychologist at the University of Pittsburgh, told The New York Times that delivering oxytocin into dogs’ eyes could have irritated their eyes, causing them to produce tears.

Bylsma said she believes that only humans produce emotional tears, as she outlined in a 2018 paper. Of course, this backs up part of Kikusui and his colleagues’ research, that humans are moved emotionally by their dogs. Then again, that was never in dispute.

“Dogs have become a partner of humans, and we can form bonds,” Kikusui said. His team has yet to test whether dogs cry when they are reunited with their pooch pals.

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Blathnaid O’Dea is Careers reporter at Silicon Republic