Bottlenose dolphins do smile during play

Humans use smiles and laughter to communicate playfulness. Now, the behaviour has been confirmed in a species of dolphin too,

Scientists found that bottlenose dolphins (Tursiops truncates) also use these friendly gestures, or “open mouth” facial expressions, to communicate during social play.

“The relaxed open mouth, seen in social carnivores, monkeys’ play faces, and even human laughter, is a universal sign of playfulness, helping animals – and us – signal fun and avoid conflict,” says evolutionary biologist Elisabetta Palagi of the University of Pisa, Italy.

“The open mouth gesture likely evolved from the biting action, breaking down the biting sequence to leave only the ‘intention to bite’ without contact.”

Dolphins of all ages are playful animals. Their antics can include acrobatics, surfing, playing with objects, chasing, and even playfighting. But it’s important their playmates don’t misinterpret playfulness for aggression.

Palagi and collaborators recorded captive bottlenose dolphins while they played in pairs or while they played freely with their human trainers.

They found the dolphins overwhelmingly “smiled” while they were playing with other dolphins. Only 1 smile event was recorded during solitary play, while 1,288 occurred during social play. Of these, 92% of smiles occurred during playtime with other dolphins.

Dolphins even tended to smile more when they were in their companion’s field of view. When that smile was seen by its playmate, the behaviour was reciprocated 33% of the time.

“We showed that dolphins are also able to mirror others’ facial expression,” says Pelagi.

“Some may argue that dolphins are merely mimicking each other’s open mouth expressions by chance, given they’re often involved in the same activity or context, but this doesn’t explain why the probability of mimicking another dolphin’s open mouth within 1 second is 13 times higher when the receiver actually sees the original expression,” says Palagi.

“This rate of mimicry in dolphins is consistent with what’s been observed in certain carnivores, such as meerkats and sun bears.”

While the researchers didn’t record sound for the study, they say that future investigations should look at the potential role of vocalisations and tactile signals during dolphins’ play.

“Future research should dive into eye-tracking to explore how dolphins see their world and utilise acoustic signals in their multimodal communication during play,” says zoologist Livio Favaro of the University of Turin, Italy.

“Dolphins have developed one of the most intricate vocal systems in the animal world, but sound can also expose them to predators or eavesdroppers. When dolphins play together, a mix of whistling and visual cues helps them cooperate and achieve goals, a strategy particularly useful during social play when they’re less on guard for predators.”

The research is published in the journal iScience.