Dolphins may ‘smile’ during play, research suggests

(CN) — As one of the most intelligent animals in the world, dolphins frequently engage in play, but exactly how whales, porpoises and dolphins communicate during play has been largely unexplored, until now, when scientists have found that bottlenose dolphins “smile” to engage playmates.

The research published Wednesday in the Cell Press’ journal iScience takes a deep dive into the social lives of bottlenose dolphins, exploring how their play can be triggered by an open mouth facial expression similar to what humans might interpret as a smile.

Elisabetta Palagi, an evolutionary biologist and the study’s senior author, was studying the play of dolphins alongside corresponding author and zoologist Livio Favaro when she began to notice a pattern. While playing together, the dolphins were repeatedly making an open mouth expression that looked a lot like a smile.

“I spent a lot of years studying play across different species, and Livio and I wanted to start studying play modalities in dolphins, too,” Palagi said in an email, describing how her and Favaro would document dolphin play and later analyze the footage for patterns.

“When in front of the pool at ZooMarine [in] Italy and after recording the first videos, we realized that playing dolphins emitted prolonged open mouth displays without any attempt to bite the playmate, and we did not see a similar behavior in any other context," she added.

Palagi and her team quickly expanded their studies, observing an additional group of dolphins at Planete Sauvage in France, and realized that the French bottlenose dolphins did the same thing.

Play is a widespread behavior that is seen across nearly all mammals, and bottlenose dolphins can engage in a variety of types of play, such as acrobatic, which typically consists of leaps and flips, and object, in which dolphins play with ‘toys’ such as coral or plastic bags.

Researchers also observed the dolphin’s social play, which can shed light on complex communication. Social play can combine other aspects of play but always involves the interaction of at least two dolphins. A juvenile bottlenose dolphin’s first playmate is its mother, but it quickly expands its social network, preferring to play with calves of a similar age.

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

Researchers observed the play of bottlenose dolphins solo, in pairs and with their trainers, filming 80 hours of play sessions over 60 days. Of the 837 recorded play sessions, researchers captured just one open mouth expression during solitary play and 1,288 open mouth expressions during social play sessions.

The dolphins also didn’t use a “smile” when playing with their trainers, preferring to use the expression when their faces were in view of another dolphin, as recorded 89% of the time.

Dolphin play frequently consists of play bites, so researchers did question whether these open mouth signals were simply the dolphins preparing to bite their playmates. While there still is the possibility that the expression could be defensive, 89.17% of the expressions were made within the visual field of the playmate, suggesting that the initiating dolphin wanted its playmate to see its smile more than it wanted to make physical contact.

But the standout finding from this study isn’t that dolphins smile at all — it’s that when one dolphin smiles at its playmate, 33% of the time that playmate will smile back. This discovery of mirroring in dolphin social play was incredibly intriguing to Palagi, who has a history of studying rapid facial mimicry in animals.

“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,” Palagi said in an email. “However, this doesn’t explain why the probability of mimicking another dolphin’s [open mouth display] within one second is 13 times higher when the receiver actually sees the original expression.”

Palagi explained that this rate of mimicry found in the dolphins is consistent with what’s been observed in certain carnivores, such as meerkats and sun bears. Both open mouth signals and rapid mimicry can be found across the mammal family tree, suggesting that “visual communication has played a crucial role in shaping complex social interactions, not only in dolphins but in many species over time,” according to Palagi.

This discovery doesn’t mean that dolphins only rely on visual cues while playing, but that they likely simultaneously refer to signals from several different senses, like touch and their strong acoustic abilities, making their social play communication styles incredibly complex.

In the future, Palagi hopes to utilize further technology, such as artificial intelligence, to study these aspects of dolphin play, as her team neglected to track the dolphins’ touches and record their vocalizations.

“Future research should also dive into eye-tracking to explore how dolphins see their world, and utilize ultrasonic audio recordings to investigate the role of multimodal communication in their playful interactions,” Palagi said in an email. “Plus, the differences between play within species and between species, as well as the potential for unique relationships between dolphins and their caretakers, remain intriguing mysteries waiting to be uncovered!”