Dogs can cry when owners come home, study suggests

Dogs can cry tears of joy when they are reunited with their owners, a small study has found.

Canines may be genuinely thrilled when they see their human companions after a long period of absence, Japanese researchers have said.

The tears are believed to deepen the bond between dogs and their owners.

The study, based on the behaviour of 22 dogs, looked at the reactions of dogs who were reunited with their owners and with other people they knew.

To test their theory, academics at Azabu University and Jichi Medical University placed strips of paper under the eyes of the dogs during normal interaction with their owners and a minute before they were reunited with them after five-to-seven hours of separation.

They discovered when the dogs saw their owners, it was the only time they shed tears. There was not the same level of increased tear production when the dogs were reunited with the people they were familiar with, but were not their owners.

To see whether the tears were linked to their emotions, the researchers applied a solution containing oxytocin, a key hormone involved in bonding, to the dogs.

After they used the hormone, they found the dogs' tears significantly increased.

While dogs are known to cry to keep their tear ducts clean, it has not been linked to their emotional response before.

"We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners," said Takefumi Kikusui, one of the authors of the study in the journal Current Biology.

While owners might be more familiar with tail-wagging or face-licking from their ecstatic pets, a dog's tears can also affect their human companion.

A dog's gaze stimulates secretion of oxytocin, making owners more nurturing or protective of their pet.

The scientists also found owners felt more desire to care for their animals when they saw them with teary eyes.

"Their tears might play a role in the deepening of mutual relationships and further leading to interspecies bonding," the researchers wrote.