Bottlenose dolphins ‘smile’ while playing

The bottlenose dolphin is among the most intelligent and charismatic marine species in the animal kingdom. Known for their sociable nature, these dolphins communicate primarily through a rich repertoire of whistles and clicks. They also maintain a playful demeanor throughout their lives, engaging in activities like jumping, spinning, and slapping the water’s surface with their fins. This playful behavior inspired evolutionary biologist Elisabetta Palagi to investigate their non-verbal expressions. Along with her colleagues from the University of Pisa in Italy, she discovered that these marine mammals exhibit a gesture resembling a human smile when interacting playfully with their companions.

Scientists analyzed 1,288 different expressions made by captive dolphins — recorded in 837 videos at two marine zoos in Italy and France — as they played in pairs and with human trainers. Although the study was conducted in a controlled environment, the findings, published Wednesday in the journal iScience, revealed that in more than 30% of cases, there was a response to the dolphins’ gesture of opening their mouths and displaying their teeth.

Notably, 89% of the recorded open-mouth expressions occurred when the dolphins’ faces were visible to their playmates. The researchers observed that when the cetaceans could see their interlocutors, their response time — averaging one second — was significantly quicker, a phenomenon the team classified as rapid facial mimicry, which has been previously studied in terrestrial mammals like meerkats and sun bears.

“Bottlenose dolphins can evoke a mirror response with their facial expressions,” says Palagi, the lead author of the study. Social play necessitates complex communication skills, as it arises from agonistic behavior, where animals react aggressively to conflict or threats. The “open mouth displays” likely have their evolutionary origins in the actions of attacking and biting. However, the study also suggests that it cannot be ruled out that in some cases, this gesture may be produced defensively.

Bruno Díaz, founder of the Bottlenose Dolphin Research Institute (BDRI), cautions against suggesting that the facial expressions of dolphins are universally distinctive. “Just because a dolphin displays different facial expressions doesn’t mean we can generalize this behavior to all dolphins,” explains Díaz, an ecology Ph.D. who did not participate in the study.

Similarly, Carmen Arija, a marine zoologist and director of Sea Wolves, notes that while the conditions in the wild differ from those in captivity, certain behaviors remain consistent. “It’s possible that this is a very basic behavior; it’s not a true smile, but it may be the closest equivalent. It likely serves a similar purpose in the marine environment,” says Arija, who was also not involved in the research.

The authors of the article acknowledge that exploring visual communication in dolphins is challenging, but environments like zoos provide valuable opportunities to analyze the subtle communicative and cognitive traits that animals may use to manage their interactions. Both Díaz and Arija agree that studying these aspects in the aquatic environment is complex.

“Having animals in zoological institutions, rescue centers, or sanctuaries enables us to make recordings, as seen in this study, allowing for much closer observation of their visual communication. It would be a crime not to take advantage of this opportunity,” argues Arija.

Although the scientists did not document the dolphins’ acoustic signals and vocalizations during play in this study, they suggest that future research should incorporate these elements along with tactile signals — such as rubbing bodies and fins with one another, which are often seen as signs of friendship during playful interactions. “Play behavior is crucial if we want to study short-distance communication. Animals don’t rely solely on visual signals; they also integrate these with other sensory modalities,” says Palagi. “Humans receive a wide range of acoustic and tactile stimuli, and I believe many other mammals and species also utilize multiple sensory channels,” she adds.

Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition