Dolphins are known for their playful nature, yet there’s still much to learn about how they, along with other marine mammals, communicate while engaging in playful activities. Recent findings published on October 2 in the journal iScience by Cell Press reveal that bottlenose dolphins (Tursiops truncatus) use an “open mouth” facial expression, which resembles a smile, to convey messages during social play. This expression is almost always displayed when the dolphins are within sight of their companions, and when they notice a “smile,” they reciprocate it about 33% of the time.
Dolphins are known for their playful nature, yet there’s still much to learn about how they, along with other marine mammals, communicate while engaging in playful activities. Recent findings published on October 2 in the journal iScience by Cell Press reveal that bottlenose dolphins (Tursiops truncatus) use an “open mouth” facial expression, which resembles a smile, to convey messages during social play. This expression is almost always displayed when the dolphins are within sight of their companions, and when they notice a “smile,” they reciprocate it about 33% of the time.
“We’ve discovered a unique facial expression, the open mouth, in bottlenose dolphins, and we’ve demonstrated that dolphins can also imitate others’ facial expressions,” explains Elisabetta Palagi, a senior author and evolutionary biologist from the University of Pisa. “The consistent use of open-mouth signals and quick mimicry across the mammal family tree suggests that visual communication has been vital in developing complex social interactions, not just in dolphins but across numerous species over time.”
Dolphin play often includes activities like acrobatics, surfing, interacting with objects, chasing, and play-fighting, so it’s crucial to not mistake these behaviors for aggressive actions. While many mammals employ facial expressions to show they are being playful, the idea that marine mammals do the same hasn’t been thoroughly examined until now.
“The open mouth gesture likely evolved from the biting action, simplifying it to convey the ‘intention to bite’ without actual contact,” notes Palagi. “The relaxed state of an open mouth, seen in social carnivores, playful monkey faces, and even human laughter, is a universal indication of playfulness, helping both animals and humans signal enjoyment and reduce conflicts.”
To delve deeper into whether dolphins use visual cues to express playfulness, researchers observed captive bottlenose dolphins as they interacted in pairs and during sessions with their human trainers.
The findings indicate that dolphins regularly display the open mouth expression while playing with other dolphins but not while interacting with humans or during solitary play. Only one instance of an open mouth expression was recorded during solitary play, whereas there were 1,288 occurrences noted during social play sessions, with 92% of those happening during dolphin-only interactions. Dolphins were more likely to show the open mouth expression when their companions could see them — 89% of all recorded instances happened in such contexts — and when they noticed the “smile,” their playmates reciprocated it 33% of the time.
“Some might argue that the dolphins are simply mimicking each other’s open mouth expressions purely by chance, considering they often engage in the same activities or contexts. However, this does not account for the fact that the likelihood of mirroring another dolphin’s open mouth expression is 13 times higher when the observing dolphin can see the original expression within one second,” explains Palagi. “This level of mimicry in dolphins aligns with what has been documented in certain carnivorous species like meerkats and sun bears.”
The research team did not capture the dolphins’ sounds during play, indicating that future investigations should focus on the role of vocalizations and tactile communication during playful encounters.
“Upcoming studies should utilize eye-tracking to better understand how dolphins perceive their environment and apply vocal signals within their multimodal communication during play,” suggests corresponding author and zoologist Livio Favaro. “Dolphins have one of the most complex vocal systems in the animal kingdom; however, vocalizations can also make them vulnerable to predators or unwanted listeners. During playtime, dolphins may combine whistling with visual signals to enhance cooperation and achieve their objectives, a method particularly beneficial during social interactions when they may be less vigilant for threats.”
