Foreign dolphins encountered in the Bahamas. Things went well.

In 2013, a pod of 52 Atlantic spotted dolphins, driven to migrate by unknown forces, left their home on the Little Bahama Bank in the northern Bahamas. They traveled 100 miles south to the Bimini island chain, a destination already inhabited by a community of 120 Atlantic spotted dolphins.

When groups of social mammals get together, things can get tense. Clashes between chimpanzee communities, for example, are notorious for their violence. Adult male mammals, especiallyare keen to defend territory and access to females.

But for the Atlantic spotted dolphins at Little Bahama Bank and Bimini, the mixing and mixing seems to have gone pretty well, the scientists found.

Two teams of researchers recently published papers on the growing dolphin community. Their analyses, unlike the dolphins, were not mixed and offered independent confirmation that dolphins from different groups formed strong bonds in a short period of time. This rare event provides new clues about how these intelligent mammals organize their complex societies and may help predict what could happen if climate change brings populations closer together.

Denise Herzing, a marine mammal behavioral biologist at the nonprofit Wild Dolphin Project, and her colleagues have observed dolphins on the Little Bahama Bank for nearly 30 years and began tracking all 52 dolphins when they left.

“We were curious how they fit in,” she said. “It’s kind of a natural experience.”

Another team, the Dolphin Communication Project, has observed dolphins in Bimini for 20 years. “All of a sudden we saw so many adults that we didn’t know,” said Nicole Danaher-Garcia, a behavioral ecologist with the group. She was referring to dolphins, not other dolphin researchers, of course.

Aquatic mammals often spend their entire lives forming close bonds within their native group, Dr. Danaher-Garcia said. But in Bimini, they were forming new friendships with strangers in just a year.

Dr. Danaher-Garcia’s team tracked dolphins that spent time together from 2013 to 2018 and analyzed how the animals touched each other. “Often you will see them rubbing their pectoral fins against each other. Looks like they’re playing pie,’ she said. A dolphin may rub its forehead on a pal’s belly, indicating an even stronger bond. “You have to love them,” she said, “and if they allow you to, they have to trust you.” Such friendly gestures were common in men of the different groups, the team reported this week in the journal Royal Society Open Science.

The team did not observe any aggression between the newcomers and the original Bimini crew, the kind of conflict often seen in the wild when groups of mammals coalesce.

“It’s very unusual,” Dr. Danaher-Garcia said. Instead, his team saw the animals socialize, play, and become frisky through the original group lines, behavior more akin to that of bonobos.

She said it was possible that “like bonobos, they use sexual behaviors to ease tension.” Sometimes this bacchanal can look like a dolphin ball. “You can’t really tell who’s touching who and what’s going on,” she said.

Like bonobos and chimpanzees, dolphins live in fission-fusion societies where they forge strong bonds between individuals, but can break those bonds and forge new ones. This type of bond between individuals from different groups is not seen in many mammals, said Diana Reiss, a marine mammal scientist and cognitive psychologist at Hunter College, who was not part of either study. Seeing such social flexibility within groups that didn’t live together before “is pretty exciting,” Dr. Reiss said.

Dr Danaher-Garcia’s team suspect that Bimini’s geography, with extensive shallows as well as abundant access to deep waters for foraging, allows for friendlier interactions because the dolphins likely don’t need to fight for space.

But that doesn’t mean it was all frictionless. Dr. Herzing’s group observed aggressive behaviors, such as dolphins slapping or head-banging, that are typical when males compete for mating opportunities. His group mapped cetacean associations from 2015 to 2020 and published the results last week in the journal Marine Mammal Science. But the fights observed by Dr. Herzing’s team are not unusual and can occur within the same pod of dolphins.

Dr. Herzing’s group has yet to publish its analysis of the types of touches that occurred in the newly mixed group. This team stayed on a boat further offshore to watch the dolphins for longer days during the summer. By contrast, Dr. Danaher-Garcia’s project had a limited sample size that was more male-focused, as opposed to male and female, Dr. Herzing said, and might have missed some aggressive encounters.

“They probably didn’t see any aggression, probably because there was nothing to fight for,” she added.

There may also be a difference in how the two studies rank what counts as aggression, Dr. Herzing and Dr. Danaher-Garcia noted.

Further research is needed to determine if mixed pods of dolphins become increasingly intertwined through mating. The Wild Dolphin Project, Dr. Herzing’s team, gets the scoop on this by collecting dolphin droppings and analyzing the genetic material they contain to reveal the parentage of the dolphins.

Guido J. Parra, a behavioral ecologist at Flinders University who was not involved in either study, said it was useful to look for these interactions. An understanding of social connections could help reveal how groups of animals might respond to environmental changes and aid in conservation. Researchers still have a lot to learn about the ecological factors that drive clustering, the role of individuals in forming social structure, and the costs and benefits of clustering, Dr Parra said.

This will be important as different populations of dolphins can be brought together. For example, in Bangladesh, rising seas encroached on a land boundary and brought river dolphins into contact with another species of dolphin in the ocean, Dr Herzing said.

“We don’t know exactly how the species will fare,” she said.

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