Dolphins at Play: A Dive Into the Evolution of Complex Communication in Marine Mammals

By Dr. Chinta SidharthanReviewed by Lily Ramsey, LLMOct 10 2024

Playful behavior in animals, defined as spontaneous behavior without any specific, immediate, or obvious function, has evolved independently among taxa.

It is classified into various types based on the presence of one or more players, the involvement of movement patterns, and the manipulation of objects during play.

In a recent study published in IScience, researchers from Italy and France examined play and visual communication in bottlenose dolphins, focusing on the display of open mouth during social play. They examined whether the behavior evolved in social groups of dolphins from a common ancestor or due to similar environmental pressures.

​​​​​​​Study: Smiling underwater: Exploring playful signals and rapid mimicry in bottlenose dolphins. Image Credit: Kavindu Induranga/Shutterstock.com

Background

Playful behavior is common in vertebrates and invertebrates and can take various forms, such as social or solitary play involving complex communication. Effective communication is essential during play for animals to avoid aggression.

The open-mouth display during play is believed to be a common behavior that has evolved from biting, which has been observed in carnivores, marine mammals, and primates.

Bottlenose dolphins are a species that are highly playful in social groups and present an ideal group to study the evolution of playful behavior in marine mammals. However, the research on visual signals such as open mouth display during play in bottlenose dolphins remains limited.

About the Study

In the present study, the researchers investigated the role of open-mouth display during various forms of play involving bottlenose dolphins. These forms included solitary play, play between dolphins, and play between humans and dolphins. The study examined whether the open-mouth display is an intentional signal for communication between playmates.

The researchers used systematic video analysis and statistical modeling to explore two hypotheses about the evolution of the open-mouth display behavior during play in bottlenose dolphins.

The study involved 22 bottlenose dolphins that were residing at two marine facilities in Italy and France, and the researchers divided the dolphins into different social groups and filmed their free play sessions outside of feeding and training hours.

All underwater activity was captured through large glass windows, which allowed uninterrupted filming during social and solitary play sessions.

The researchers then analyzed the videos frame-by-frame and focused on three types of play — solitary, intraspecific (between dolphins), and interspecific (between humans and dolphins).

Each of the play sessions was further categorized based on the use of objects during solitary play or the engagement of a playmate during intraspecific play sessions. Apart from open-mouth display, play bite behavior and rostrum touching were also categorized in the recordings.

One of the hypotheses tested in the study assumed that the purpose of the open-mouth display was playful interaction and, therefore, predicted that it would occur more during intra- or inter-specific play and not during solitary play.

The other hypothesis examined whether rapid facial mimicry occurred in bottlenose dolphins. It investigated whether a dolphin mimicked the open-mouth display seconds after detecting it in its human or dolphin playmate. The researchers used various statistical models, such as the generalized linear mixed model, to test both hypotheses using data obtained from the video recordings.

Major Findings

The study found that bottlenose dolphins engaged in bidirectional and highly interactive play, which was in contrast with real aggression. During play, the dolphins allowed their playmates to counterattack and be involved in behaviors such as tail slapping, fleeing, biting, and chasing.

Furthermore, open-mouth display was observed primarily during interspecific play involving pairs or groups of dolphins.

It occurred largely when the sender and receiver of the display were within visual range of each other. Open-mouth displays were also observed more frequently during intraspecific play between dolphins than during interspecific play between humans and dolphins.

Over 89% of the open-mouth displays occurred when the dolphins were in each other’s line of sight, and when the other dolphin detected the open-mouth display, 33.16% of the behaviors resulted in rapid facial mimicry, which suggested that this form of display was a mode of intentional communication.

These findings indicated that both open-mouth display and rapid facial mimicry were social signals indicating that messages were perceived during play.

Interestingly, open-mouth displays were not linked to behaviors involving aggression, such as jaw claps, and during play bites, the dolphins aimed away from sensitive areas such as the rostrum.

Conclusions

Overall, the findings indicated that dolphins engaged in active and adaptive play based on social contexts and involvement in intraspecific play and participated in complex forms of communication such as open-mouth display and rapid facial mimicry.

These results suggested that playful behavior in bottlenose dolphins may have evolved as part of the complex and sophisticated communication system within the species.