SMART NEWS

Bottlenose Dolphins ‘Smile’ at Each Other During Playtime, Study Finds

Researchers still don’t know what the open-mouth facial expression means or whether it’s akin to smiling in humans—but several animals make a similar face during play

Sarah Kuta

Daily Correspondent

Underwater view of dolphin with its mouth open
Dolphins living in captivity often make an open-mouth facial expression while playing with each other. Zoomarine, Italy

Bottlenose dolphins “smile” at each other while playing, making open-mouth facial expressions that are similar to those used by other animals, new research suggests.

These findings, published last week in the journal iScience, may offer new insights into the evolution of mammals—including humans.

“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,” says study co-author Elisabetta Palagi, a cognitive primatologist at the University of Pisa in Italy, in a statement.

Researchers noticed that bottlenose dolphins (Tursiops truncatus) living in captivity often made open-mouth facial expressions while playing with each other—but they did not tend to “smile” in other situations. This made the scientists curious to learn more about the behavior. Though past studies have looked at auditory communication among dolphins, few have focused on other modes of communication, such as body language.

The researchers captured 80 hours of video footage of 22 bottlenose dolphins living at two wildlife parks: Zoomarine Rome in Italy and Planète Sauvage in France. When they analyzed the recordings of these social, highly intelligent marine mammals, they counted 1,288 open-mouth displays during playtime sessions.

While the vast majority of these “smiles” occurred when dolphins were playing with one another, a few also occurred during play with humans. Nearly 90 percent of the open-mouth facial expressions happened when the dolphin’s playmate could see their face.

In instances where one dolphin saw another “smiling,” the playmate replicated the open-mouth expression—or “smiled” back—roughly 33 percent of the time. The mammals mimicked their playmate’s face quickly, too, often flashing a grin in less than one second.

Though researchers observed dolphins making the open-mouth expression during playtime, it’s not clear what the behavior means, nor why the dolphins are “smiling.”

Researchers also don’t know whether a “smile” means the same thing to dolphins as it does to humans. Other creatures, such as meerkats, wolves, cats and orangutans, have been observed making a similar, open-mouth “play face”—but that doesn’t necessarily mean they are feeling or communicating a particular mood.

“There is a strong debate if, in nonhuman animals, the act of smiling or laughing … is driven by emotional arousal or intention,” Palagi tells Science News’ Gennaro Tomma. “We were extremely conservative and simply referred to [it as a] facial display.”

Researchers also didn’t analyze whether the dolphins were making sounds while smiling—so, one possibility is that they were simply opening their mouths to make vocalizations.

The study focused exclusively on dolphins living in captivity, so it remains an open question as to whether wild dolphins also “smile” at each other—and, if so, in what contexts.

“Free-living dolphins have much larger spaces to interact and chase one another while playing, and many times are found in waters with reduced visibility,” says Luciana Moller, a marine biologist at Flinders University in Australia who was not involved with the research, to New Scientist’s James Woodford. “In these circumstances, visual signals may not be as effective as acoustic signals.”

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Sarah Kuta

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.