- When we reunite with our tail-wagging, face-licking canine pals, they might tear up – a reaction likely linked to the release of oxytocin
- Study published last month showed dogs ‘significantly’ increased tear production when seeing owners after 5 to 7 hours of separation
Dog owners know the pure joy of returning home from a long trip to be greeted by their tail-wagging, uncontrollably jumping, face-licking companion.
But those ecstatic canines might be shedding more than just fur on your clothes – they might also be tearing up, according to a new study published last month in the journal Current Biology.
“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 study’s authors, who called the discovery a possible “world first”.
The scientists measured the amount of tears in the dogs’ eyes with the widely-used Schirmer test, which consists of placing a specialised strip under the eyelids.
For a baseline reading, they performed the test on dogs during a normal interaction with their owner.
When dogs were reunited with their owners after five to seven hours of separation, they “significantly” increased tear production in the ensuing five minutes, the researchers found.
They also discovered that the dogs’ volume of tears was higher when they reunited with their owner versus other people the dog was familiar with.
According to the researchers, this reaction to tear up is likely linked to the release of oxytocin, nicknamed the “love hormone,” because of its connection with building bonds.
The scientists then sought to test whether the tears might have an emotional impact on the owners. To do so, they asked the owners to rank various photos of their dogs with and without artificial tears by how much they wanted to care for them.
“The dog photos with artificial tears were ranked significantly higher than the normal tearless dog photos,” the Japanese research team wrote.
“It is possible that the dogs that show teary eyes during interaction with the owner would be cared for by the owner more,” hypothesised Kikusui.
In humans, the authors note, infants share their negative feelings by crying, which leads to more caregiving from parents.
Domesticated by humans like no other animal, dogs have developed specific communication skills over time. Eye contact has been shown to play a role in forming the relationship between a dog and its owner.
In future studies, the researchers would like to test if dogs similarly produce tears when meeting other canines.
Apart from dogs, are there other animals that cry when they are happy?
Before the study published in Current Biology, many scientists believed humans were the only animals that produced tears when they felt sad or happy.
While many animals such as cats, horses and rabbits do have tears, it is mostly to clear debris from their eyes. In fact, if a zookeeper notices tears in an animal’s eyes, it is usually because of an eye infection.
This does not mean animals do not have feelings, though. They too can experience a wide range of emotions. However, they express how they feel in different ways – through sounds and body language.