Do dolphins really smile and why an open mouth is not always a sign of a good mood

Scientists have conducted a new study on dolphins' play and found that their smile-like facial expressions do not always indicate their good mood. Experts call for caution in attributing human behavior to creatures whose intentions we can only guess.

The study claims that an open mouth is a form of communication. And most often, dolphins use it among themselves, Science News writes.

Scientists have long known that dolphins can exhibit behaviors that humans often associate with smiling. Other animals, such as primates, can open their mouths in a relaxed manner to communicate during playful contexts. "It’s a signal that communicates, ‘Look, I’m just playing!’. Like when we put a smiley face on a cell phone message that could be misleading," says Elisabetta Palagi, a comparative ethologist at the University of Pisa in Italy.

However, this behavior has never been studied in depth. Thus, Palagi and her colleagues recorded nearly 900 play sessions among 22 captive bottlenosed dolphins (Tursiops truncatus), capturing nearly 1,300 "smiles" from 17 animals. The researchers filmed dolphins playing alone, with other dolphins, and with humans.

As a result of the study, the team found that the dolphins mostly demonstrated their open-mouth behavior when playing with a companion, usually another dolphin. When the animals played alone, they almost never "smiled". In addition, about 90 percent of the open-mouth expressions were performed when the dolphins were in the field of view of their companion.

In addition, when one of these "smiles" was seen by another dolphin, in about a third of the cases, the former also "smiled" back in less than a second. According to Palagi, this is the same time that elapses between a human perceiving a facial expression and then displaying it.

According to scientists, an open mouth is a very sophisticated form of dolphin communication that can be used in conjunction with acoustic signals. However, it is difficult to say whether it had the same evolutionary origin as the human smile. Most likely, it serves the same function, as the context and manner in which the smile occurs is the same as in humans.

However, animal behavior expert Erin Frick, who was not involved in the study, says that we should not take the dolphin's "smile" as a sign of good mood or a message of play, "Being able to see some evidence that’s demonstrating [dolphin’s open-mouth behavior] in a play context is really great. But I don’t think open mouths are always communicating play," she says.

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