An emotional state was shown to correlate with tear production in dogs for the first time ever. When reunited with loved ones, they cry tears of happiness.
Researchers in Japan found that dogs may become quite emotional upon seeing their master again after being apart for a long time, and they theorized that this strong emotional response strengthened the link between canines and their masters.
As reported by the BBC, this research is limited in scope since it only looked at the responses of 22 dogs when they were reunited with their owners or other familiar individuals.
Researchers from Azabu University and Jichi Medical University put strips of paper beneath dogs’ eyes during normal interactions with their owners and for one minute before the canines were reunited with their owners after a five- to seven-hour absence.
They found that the only time the dogs cried was when they saw their owners. When the dogs were reconnected with persons they knew but weren’t their owners, they didn’t show the same amount of increased tear production.
The dogs were given a solution containing oxytocin, a crucial hormone involved with “bonding,” to determine whether or not the tears were emotional in nature.
They discovered that the dogs cried far more often after administering the hormone. Tear-shedding in dogs has long been accepted as a necessary part of their grooming routine, but it has never before been connected to their emotional state.
“We had never heard of the fact that animals produce tears in pleasant conditions,” said Takefumi Kikusui, one of the authors of the research published in the journal Current Biology.
Dogs’ tears may have an emotional impact on their human companions, even if owners are more likely to notice other signs of happiness, such as tail wagging or face licking. The gaze of a dog may make its human companion more caring and protective via the production of oxytocin.
The researchers also discovered that seeing their animals in distress prompted owners to want to take better care of them. The researchers speculated that the two species’ tears could have a role in strengthening their ties with one another.