Anyone with a dog will know the excitement they show when you walk through the door, especially if you've been gone a few hours. From the wagging tail and the ears sticking up, your four-legged friend don't hide their emotions.
Yet a group of researchers in Japan have found that dogs also display their emotions with tears of joy when their owners have been gone for a prolonged period of time. Furthermore, these tears are said to strengthen the bond between the dog and their owner, according to an article in the BBC.
The study involved a group of 22 dogs whose behavior was studied under different circumstances. Researchers found a distinct difference in the dogs' responses to meeting their owners, and just people they knew: Tears were reserved for the pets' owners.
Researchers from Azabu University and Jichi Medical University tested their theory by placing paper strips under the eyes of the dogs in different sets of circumstances. They studied the normal interaction between the dogs and their owners, and then they separated them for periods of 5 to 7 hours.
The researchers found that the only time dogs shed tears was after the prolonged separation from their owners. When being reunited with familiar faces who were not their owners, the dogs didn't have the same reaction.
The study then went one step further to determine if the tears were a purely physical or emotional reaction. By applying a solution containing oxytocin, (a hormone linked to bonding), researchers found that the dogs produced far more tears.
While it has been acknowledged that dogs can have watery eyes and produce tears to help clean their eye ducts, the study has been the first to discover that dogs produce tears of joy.
As Takefumi Kikusui, one of the authors of the study that was published in Current Biology, explained, "We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners."
Furthermore these tears also play a part in developing a strong bond between the owner and their dog. When looking at a teary-eyed furry friend, an owner has a physical response. There is a stimulation in the secretion of oxytocin.
"Their tears might play a role in the deepening of mutual relationships and further leading to interspecies bonding," explained the researchers.
After all, when seeing their pets' eyes filled with tears, owners will have a stronger desire to be more nurturing and protective, as the BBC article pointed out.
While the study was limited to just 22 dogs, anybody who is blessed to own a dog can see the reaction of their pet when they are reunited after a period of time, and maybe see those tears of joy, too.
