Many mammals and birds tend to have antagonistic and hostile reactions to contact with other groups outside their community. But it’s not always like this. the bonobos, one of the closest living relatives to people, are an exception. But there are not only terrestrial species that are out of the norm. Recently published research in Royal Society Open Science shows a partial merger of two populations of spotted dolphins (Stenella frontalis) of the Atlantic. Part of a community located in the north migrated 160 kilometers to another that is in the south. Among the immigrant individuals were dolphins of all ages and of both sexes. The affiliative contacts between the dolphins indicate that they were forming social relationships.
Nicole Danaher-Garciabiologist, member of the Dolphin Communication Project (DCP) and one of the authors of this research, highlights that the particularity of these results is that, once they migrated, they have stayed there: “It is usually unheard of for this to happen in terrestrial mammals. Even bonobos sometimes get together and spend weeks or months together, but often they split up again. These dolphins are still mixing. Therefore, it seems that they are tolerant of strangers.” Another of the most interesting issues of this new union is that, although DNA tests are required to verify the paternity of the new offspring, there have been matings between males from the north and females from the south.
This investigation started unexpectedly and without human intervention. The study project to which Danaher-García belongs has been analyzing the dolphin population in the southern Bahamas, this community is located specifically in Bimini, since 2001. From the beginning until 2012, no new adults were observed, beyond young individuals. who were beginning to form part of the adult list. The population was approximately 120 individuals. But in 2013, they suddenly observed a more or less large new group of adults of various ages and of both sexes in that territory. It was then that they began to follow them: during the first year they saw dolphins from the south mixed with others from another community.
“The following year we saw them much more frequently and were able to confirm that they are from an area called White Sand Ridge, in the northern Bahamas,” he explains. The original social structure was already clear and, although an alteration of relations could be expected, both communities merged and even formed new links, which in some cases are strong. The White Sand Ridge dolphin population has been studied for about 30 years. In 2012, and after a variation in the number of spotted dolphins, the total rose to 85.
In total, almost fifty individuals were sighted from White Sand Ridge in Bimini during the five years that followed this migration. Until 2019 they continued to see northern dolphins, but this activity stopped with the arrival of covid. However, Danaher-García comments that there are people who have seen individuals from both groups. “Maybe some of them went back north, but there is a large group that stayed,” she concludes.
It is not the only recent study that shows the associative capacity of dolphins and their possible similarity to humans. An investigation published in PNAS shows that dolphins are the second species capable of weaving a greater network of alliances behind people. The results of the study, which analyzed 121 male Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Shark Bay (Australia) between 2001 and 2006, reveal that both dolphins and people form strategic intergroup alliances between unrelated individuals. Within this network, the average number of adult males with which each male directly associated was 22. Some were connected to as many as fifty males. In addition, the duration with which males associate with females depends on their being well connected with third-order allies, that is, with other groups. Therefore, alliances between groups increase access to a disputed resource, thus increasing reproductive capacity.
About 40 different species of dolphins are counted, with a great variety among them and, in many cases, with very little information about it. Even among individuals of the same species there are differences in behavior. Maria Victoria Hernandez Lloreda, who belongs to the Department of Psychobiology and Methodology in Behavioral Sciences at the Complutense University of Madrid, explains that diversity in social behavior may be due to the specific circumstances of each community: “The same groups may behave in a tolerant manner with some and aggressively with others. It depends on the pressures, the social or economic situation” [entendiéndose económica como los recursos disponibles]. A published study in Nature Ecology and Evolution in 2017 concludes that the social cognition of cetaceans (both whales and dolphins) may have emerged to provide the ability to learn and use a set of behavioral strategies in response to the challenges of their social life.
“The fact of being more tolerant could explain that they also have greater flexibility and capacity for social cognition,” explains Hernández Lloreda. These social cognition capabilities allow dolphins to adopt the behavior of others, “learn from the group,” he explains. “It is not having a behavior that comes predetermined. Depending on what you learn, depending on the social environment you have, you are going to behave differently”, he details.
Jose Fco. Zamorano Abramson, from the Center for Research in Social Complexity of the Universidad del Desarrollo, Santiago (Chile), points out: “How is it that one learns? How is it that the same species behaves differently? Perhaps it is because it can be said that in this group they have a tradition, a way of behaving. There we speak that these groups present cultural traditions. Some differences can be explained, because they have learned it socially from their family or group members and the others do it in another way because they learned it that way in their community”.
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