Dolphins have an irresistible charm for people. They are extremely playful at all ages and often play alone, surfing the waves, leaping into the air, performing flips and striking the water with their tail flukes.
They also play with whatever they find in the ocean – sponges, corals, sticks, plastic bags and floating buoys.
Their play is also social. Bottlenose dolphins (Tursiops truncatus), which live in temperate and tropical waters worldwide, including the African coasts, play with other dolphins in the first weeks of life. The mother is the first playmate and then the dolphin calf expands its social network. This species of dolphin offers an ideal model to study how animals communicate through play.
When we humans see facial expressions like relaxed, open mouths, our faces automatically mimic them within milliseconds. This is called rapid facial mimicry. It’s a reflex, kicking in without us even thinking about it. In humans and many other animals too, rapid facial mimicry helps synchronise movements during play.
Read more: How insight into southern Africa's dolphins is being deepened
Until now, the role of facial communication in managing playful encounters between dolphins remained a mystery. In our research, we uncovered the presence of a distinct facial display, the open mouth, in bottlenose dolphins. This expression is most commonly observed during playful interactions with other dolphins, especially when the sender is within the receiver’s line of sight.
Our discovery sheds new light on how dolphins use subtle facial cues during social play.
Sophisticated communication
Dolphins rely heavily on visual cues to navigate their social and physical worlds. But their limited facial muscle movements make studying their expressions quite challenging.
However, dolphins’ playful social behaviour and the way they direct signals to each other’s visual field is similar to what other mammals do. This suggested to us that dolphins might be using facial expressions to convey information.
Certain environments favour specific ways to pass on messages. Dolphins communicate through one of the most intricate vocal systems in the animal world. They use high-pitched whistles to recognise each other and to interact socially. This probably evolved because they live in murky waters where visibility is low, forcing them to rely on sound. However, sound can also expose them to predators or eavesdroppers.
We also already knew that when they are in clear water, or when dolphins are close to each other, they can shift to visual communication. We surmised that this would make facial expressions crucial for quick, two-way exchanges.
When dolphins play together, a mix of whistling and visual cues helps them cooperate and achieve goals. This strategy is particularly useful during social play when they’re less on guard for predators.
Prior research had shown that when dolphins communicate with other species, they are very interested in whether their audience is paying attention. This suggested that they are aware of their receiver’s focus and adjust their behaviour accordingly. It highlighted their sophisticated communication abilities beyond just vocal signals.
What almost 1,300 dolphin smiles told us
We filmed 22 captive dolphins for 80 hours over 60 days. During this time, they held 837 free play sessions. During these play sessions, the dolphins performed acrobatics on their own, and also played with humans, and also with other species and other dolphins.
We recorded a total of 1,288 open mouth events or dolphin smiles.
Studying dolphin visual communication in controlled settings allowed us to capture insights into their subtle interactions. However, our study was also limited because the dolphins we studied were not free.
Future research could be carried out in wild dolphins. This would need the use of artificial intelligence, observing the way dolphins look at each other (eye-tracking), and ultrasonic recordings. This would improve our understanding of multimodal communication and differences between dolphins playing with each other and playing with other species.
New finding: dolphins copy each other’s smiles
We were surprised to realise that dolphins not only use open mouth expressions while playing, but that they are able to mirror the facial expressions of others.
The discovery of rapid facial mimicry in dolphins is one of the standout findings from this study. Nobody knew that this mimicry was present in dolphins.
We investigated whether the dolphins were merely mimicking each other’s open-mouth expressions by chance, given they’re often involved in the same activity or context.
But we found that the probability of mimicking another dolphin’s open mouth within one second was 13 times higher when the receiver dolphin saw the original expression. The animals increased their open mouth display mostly after perceiving others doing the same.
This rate of mimicry in dolphins has been observed in certain carnivores, such as meerkats and sun bears.
We also looked into the question of whether open mouth displays by dolphins were preparations for biting instead of a signal. However, in over a third of cases (33.16%), these dolphin smiles triggered a similar open mouth response from the receiver.
In the other 66.84% of cases the receiver did not smile back and the initiating dolphin didn’t bite its playmate. This suggests that the behaviour may have evolved from a bite-prevention strategy into a form of communication, where the original function has been transformed into a social signal.
Cetaceans (whales, dolphins and porpoises) are closely related to artiodactyls — a group of mammals that includes deer, camels, boars and hippos. These land-dwelling relatives haven’t been widely studied for play communication. But exploring these connections could provide insights into how communication evolved.
We are still unravelling the evolutionary origins of play and how animals fine-tune their playful behaviours. But one thing is clear: open-mouth signals and rapid mimicry appear repeatedly across the mammal family tree.
This suggests that visual communication has played a crucial role in shaping complex social interactions, not only in dolphins but in many species over time.
Elisabetta Palagi does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
This article was originally published on The Conversation. Read the original article.
