Just like you, your dog may tear up when you are reunited, a new study finds.
In an experiment with 22 dog-owner pairs, researchers found that dogs produced tears when they saw their owners after spending hours apart and that the behavior may be related to the release of the bonding hormone, oxytocin. The researchers also found that tears in dogs’ eyes spark a desire in people to care for the animals, according to the report published in Current Biology.
“Dogs have a unique ability to interact with humans,” said study coauthor Dr. Takefumi Kikusui, a professor at the Azabu University School of Veterinary Medicine in Sagamihara, Japan.
“We found that teary eyes of dogs facilitate human caregiving,” Kikusui said in an email. “Dogs have become a partner of humans, and we can form bonds. It is possible that dogs that show teary eyes during interaction with the owner would be cared for by the owner more.”
Kikusui said the idea for the study came after he saw tears in the eyes of one of his standard poodles.
“I had one female who was pregnant six years ago,” he said. “When she was nursing her puppies her face became so cute (she is always cute, but this was more).”
Conversations about what he had observed “gave me the idea that oxytocin, which is the maternal hormone, might increase tears,” Kikusui said. “We previously observed that oxytocin is released in dogs and owners when they are interacting. So we conducted the reunion experiment.”
For the experiment Kikusui and his team first measured the amount of tears that was typically in the dogs eyes to get a baseline. Next, the dogs were sent to doggie daycare for five to seven hours. When the pups and owners were reunited, the researchers found more tears in the dogs’ eyes than they observed at baseline.
The researchers next performed the same experiment, but instead of having the dogs reunited with their owners, the pups were brought together with a person who was familiar to them, but not the owner: the dogs’ produced significantly less tearing than they had when reunited with the owner.
To look at the possibility that tearing might have evolved to boost owners’ attachment for their dogs, the researchers asked a group of people to look at photos of dogs with and without artificial tears in their eyes and then to rate how much they wanted to care for the dogs in the photos. Dogs with teary eyes sparked a greater urge to care.
The researchers next squirted eye drops containing oxytocin in 11 of the study dogs’ eyes and placebo eye drops in the other 11 dogs’ eyes. Then they repeated the procedure with the type of eye drops given to the dogs reversed. When dogs got oxytocin they teared up, but not with placebos.
The new study is “fascinating,” said Dr. Nicholas Dodman, a professor emeritus at the Cummings School of Veterinary Medicine at Tufts University, CEO and president of the Center for Canine Behavior Studies and author of “Pets on the Couch: Neurotic Dogs, Compulsive Cats, Anxious Birds and the New Science of Animal Psychiatry.”
Dodman hasn’t noticed dog tears himself, but he suspects that that may be because other dog behaviors — like whole body wiggling, tail wagging and jumping up and down — may overshadow this more subtle response.
“But I can imagine that it does happen,” Dodman said. “I always thought they were more like us than many would think. It’s a charming study.”
The research suggests that “dogs may have a greater attachment to their owners than we previously thought they did,” said Dr. Katherine Houpt, an emeritus professor of animal behavior at the Cornell University College of Veterinary Medicine.
Other research suggests that dogs parted from their owners behave very much like children separated from their mothers, Houpt said. Researchers have used a test originally designed to look at attachment in children called the Ainsworth Separation Test.
In that test, children and their mothers start out in a room together along with another person unknown to the child, Houpt explained. When the mother leaves the room, the child becomes upset and won’t approach the stranger. Once the mother came back, the child feels braver and will approach the stranger.
When the test was used in dogs, “they acted like the children and would stand at the door waiting for the owner to come back,” Houpt said. “When the owner came back, the dogs were willing to play with the stranger.”
While Houpt also hasn’t noticed dogs tearing up, she said “I did notice that our dog would jump higher in the air the longer we were away.”