The bottlenose dolphin is one of the most intelligent and charismatic marine species in the entire animal kingdom. They are sociable and use sound as their main means of communication, through an extensive repertoire of whistles and clicks. In addition, they maintain a playful attitude throughout their lives: they jump, do pirouettes and hit the surface of the water with their fins. This behavior motivated evolutionary biologist Elisabetta Palagi to investigate the non-verbal expressions they make in the depths. This researcher, together with her colleagues from the University of Pisa (Italy), has detected that these marine mammals have a gesture similar to a human smile, when they play with other companions.
The scientists analyzed 1,288 different expressions of captive dolphins – recorded in 837 videos in two marine zoos in Italy and France – while they played in pairs and with human trainers. Although this is a study that was carried out in a controlled environment, the results of the research, published this Wednesday in the magazine iScience, indicate that in more than 30% of the cases there was a response to that gesture of opening the mouth and showing the teeth.
89% of the recorded open-mouth expressions occurred at the moment the dolphins’ faces were in the field of vision of the playmates. The scientists noticed that when the cetaceans saw their interlocutors, the speed of their response (one second) was greater, which the team classified as rapid facial mimicry, an aspect that has been previously studied in terrestrial mammals such as meerkats and sun bears. .
“Bottlenose dolphins can evoke a mirror response with facial expression,” says Palagi, lead author. Social play requires complex communication skills, as it comes from agonistic behavior, that is, animals react aggressively to situations of conflict or threat. The expressions of ‘open mouth’ have their evolutionary origin in the action of attacking and biting. On the other hand, the study also mentions that the possibility cannot be ruled out that, in some cases, the gesture is produced in a defensive manner.
For Bruno Díaz, founder of the Bottlenose Dolphin Research Institute (BDRI), it is not appropriate to suggest that facial expressions lead to saying that they are distinctive. “Although a dolphin makes different faces, it does not mean that it can be generalized to all dolphins,” indicates the doctor in Ecology who did not participate in the study. And Carmen Arija, marine zoologist and director of Sea Wolves, points out that although the conditions that an animal has are different in a wild environment, there are behaviors that do not change. “It may be very basic behavior; It’s not a real smile, but it would be the closest thing. “Probably, it may be a resource used in the sea for more or less similar purposes,” says Arija, who was also not part of the investigation.
The authors of the paper acknowledge that exploring visual communication in dolphins is challenging, but that environments such as zoos offer opportunities to analyze subtle communicative and cognitive traits that animals “could use to manage their interactions.” Díaz and Arija also agree that analyzing these aspects is complex in the aquatic environment.
“The fact that we have animals in zoological institutions, in rescue centers or sanctuaries, allows us to make recordings like in this study so that we can have much greater proximity to evaluate all their visual communication. It would be a crime not to do so,” Arija argues.
Although the scientists did not record the acoustic signals and vocalizations of the dolphins during the game in the new article, they do suggest that future research should analyze these aspects along with the tactile signals – such as rubbing the body and fins with other dolphins – which are considered signs of friendship, during playful interactions. “In-game behavior is an important aspect if we want to study short-distance communication. “Animals do not rely solely on visual signals, but also use them in conjunction with other sensory modalities,” says Palagi. “Humans receive a large amount of acoustic and tactile stimuli and I believe that many other mammals and other species also have multiple sensory channels,” he adds.
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