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Dolphins delight us with their playful frolicking, a behavior we find endearingly relatable. Scientists recently studied captive bottlenose dolphins to learn more about how they interact with each other. They noticed the dolphins, while playing with each other, communicated using an open-mouth facial expression. That expression resembled what we humans might perceive as a “smile.”
The scientists published their findings in the peer-reviewed journal iScience on October 2, 2024.
Elisabetta Palagi of the University of Pisa in Italy is a paper co-author. In a statement published in EurekAlert, she said:
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. 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.
Playfulness is a trait exhibited by many mammals. Broadly speaking, the definition of play is spontaneous open-ended actions that do not have an obvious practical function, carried out in a stress-free setting. We humans associate play with joy and fun.
However, we don’t know if dolphins have similar emotions to humans during play. All scientists can do is observe their behavior. For dolphins, play activities include acrobatics, playing with objects, chasing each other, surfing and even play-fighting. Moreover, dolphins exhibit playful behavior at all ages. It starts at a young age, between a calf and mother, before the calf expands its social network to play with others in its group.
Play also involves complex communication, since certain play actions may also be used in an aggressive context. Some mammals, the scientists said, are known to use distinct facial expressions during playtime to indicate their mood. One expression is a relaxed open mouth, seen in playful social mammals.
Palagi commented:
The open mouth gesture likely evolved from the biting action, breaking down the biting sequence to leave only the “intention to bite” without contact. 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.
The scientists studied over 80 hours of video of captive dolphins. They observed how the dolphins interacted with each other and how they interacted with their human trainers.
Dolphins playing with each other, the researchers noticed, often displayed an open-mouth expression. But, for the most part, dolphins did not display the open-mouth expression when playing alone or with a trainer.
A dolphin was more likely to display the open mouth expression when the other dolphin playmate was within its sight. Perhaps it was a way to get the attention of its companion.
And notably, the playmate would respond, mimicking the same open-mouth expression, about 1/3 of the time.
Palagi remarked:
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. This rate of mimicry in dolphins is consistent with what’s been observed in certain carnivores, such as meerkats and sun bears.
The researchers would like to continue their work by recording sounds the dolphins make when they play.
Paper co-author Livio Favaro of the University of Turin said:
Future research should dive into eye-tracking to explore how dolphins see their world and utilize acoustic signals in their multimodal communication during play. 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.
Bottom line: Bottlenose dolphins use an open-mouth facial expression when playing with each other, resembling what humans might perceive as a “smile.”
Source: Smiling underwater: Exploring playful signals and rapid mimicry in bottlenose dolphins
Read more: Dolphins may use whistles like humans use names
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