Bottlenose dolphins use human-like ‘smiles’ to invite each other to play

Dolphins are known for their playful antics, and they communicate in unique ways during these fun times.

New research has uncovered a cute way dolphins express their joy and invite others to join in the fun.

Biologists from the University of Pisa have found that bottlenose dolphins use a smile-like face to say they want to play together.

The open-mouth smile is a universal sign of playfulness, seen in many animals, including humans.

The power of a smile

Dolphins love to play around, doing things like flipping, surfing, playing with stuff, chasing each other, and pretending to fight.

The authors highlight that these activities are not signs of aggression. Facial expressions, like the open-mouth smile, help dolphins communicate their intentions and avoid misunderstandings.

The bottlenose dolphins (Tursiops truncates) use “open mouth” facial expressions when their playmates are within sight, and often, the playmates respond in kind (33 percent of the time).

“We’ve uncovered the presence of a distinct facial display, the open mouth, in bottlenose dolphins, and we showed that dolphins are also able to mirror others’ facial expression,” said Elisabetta Palagi, senior author and evolutionary biologist.

“Open-mouth signals and rapid mimicry appear repeatedly across the mammal family tree, which suggests that visual communication has played a crucial role in shaping complex social interactions, not only in dolphins but in many species over time,” Palagi explained.

They smile mostly during dolphin-dolphin play

Other animals use their faces to show they want to play, but it wasn’t known if sea creatures do the same thing. This prompted the team to undertake this study. For this, videos were made of bottlenose dolphins playing together and with their human friends.

Interestingly, the videos revealed a notable pattern: dolphins often used the smiling expression during play with their mates , but not when interacting with humans or playing alone.

The researchers saw the smiling face 1,288 times when dolphins were playing together, but only once when a dolphin was playing alone. Most of the time (92 percent), they saw it when the animals were playing with each other.

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

The author added: “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.”

In this study, the sounds made by dolphins during play were not recorded. However, the team hopes to conduct future studies to look into how sounds and touching might help them play together.

“Future research should dive into eye-tracking to explore how dolphins see their world and utilize acoustic signals in their multimodal communication during play,” added Livio Favaro, corresponding author and zoologist, in the press release.

This research sheds light on the unique communication skills adopted by these intelligent marine mammals as well as the importance of facial expressions to set the right intentions.

The findings were published in the journal iScience.