In 2013, a group 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 meet, things can get tense. For example, run-ins between chimpanzee communities are known for their ferocity. Especially adult male mammals like to defend their territory and access to females.
But for the Atlantic-spotted dolphins of Little Bahama Bank and Bimini, the mixing and mixing seems to have gone rather smoothly, scientists found.
Two teams of researchers recently published articles about the growing dolphin community. Their analyzes, unlike the dolphins, were not mixed and provided independent confirmation that dolphins from different groups forged strong bonds in a short time. The rare event offers new clues about how these intelligent mammals organize their complex societies, and could help predict what might happen if climate change drives populations together.
Denise Herzing, a marine mammal behavioral biologist with the nonprofit Wild Dolphin Project, and her colleagues watched dolphins on the Little Bahama Bank for nearly 30 years and began tracking the 52 dolphins as they left.
“We were curious to see how they were integrating,” she said. “It’s kind of a natural experiment.”
Another team, the Dolphin Communication Project, has been observing dolphins in Bimini for 20 years. “Suddenly we saw so many adults that we didn’t know,” said Nicole Danaher-Garcia, behavioral ecologist with the group. She was referring, of course, to the dolphins, not the other dolphin researchers.
The aquatic mammals often spend their entire lives forming close bonds within their home group, said Dr. Danaher-Garcia. But at Bimini, they made new friendships with strangers in just a year.
The team of dr. Between 2013 and 2018, Danaher-Garcia tracked which dolphins spent time together and analyzed how individual animals touched each other. “You’ll often see them rubbing their pectoral fins together. It’s kind of like they’re playing patty cake,” she said. A dolphin may rub its forehead on a friend’s belly, indicating an even stronger bond. “You have to like them,” she said, “and if they allow you to do that, they must trust you.” Such friendly gestures were common among men from the different groups, the team reported this week in the journal Royal Society Open Science.
The team observed no aggression between the newcomers and the original Bimini crew, the kind of conflict often seen in nature when groups of mammals coalesce.
“That’s very unusual,” said Dr. Danaher-Garcia. Instead, her team watched the animals socialize, play, and get frisky about the original group lines, behavior more akin to that of bonobos.
She said it was possible that “like bonobos, they use sexual behavior to reduce tension.” Sometimes this bacchanalically resembles a ball of dolphins. “You can’t really see who’s touching who and what’s going on,” she said.
Like both bonobos and chimpanzees, dolphins live in fusion societies, where they form strong bonds between individuals, but can sever those bonds and forge new ones. This kind of bonding between individuals in 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. To see such social flexibility within groups that previously did not live together “is pretty exciting,” said Dr. travel.
The team of dr. Danaher-Garcia suspects that Bimini’s geography, with ample shoals and abundant access to deep water for foraging, makes for more conversational interactions because the dolphins probably won’t have to fight for space.
But that doesn’t mean it was all frictionless. The group of Dr. Herzing saw aggressive behavior, such as beating or ramming dolphins, which are typical when males fight for mating opportunities. Her group mapped cetacean associations from 2015 to 2020 and reported the results last week in the journal Marine Mammal Science. But the battles that Dr. Herzing has been observed are not uncommon and may occur within a single group of dolphins.
The group of Dr. Herzing has not yet published her analysis of the types of touches that occurred in the newly mixed group. That team stayed on a boat further offshore during the summer to observe the dolphins for longer days. In contrast, Dr. Danaher-Garcia limited sample size that focused more on men, as opposed to men and women, said Dr. Herzing, and possibly missed some aggressive encounters.
“They probably didn’t see any aggression, probably because there was nothing to fight about,” she added.
There may also be a difference in how the two studies classify what counts as aggression, noted Dr. Herzing and Dr. Danaher-Garcia op.
More research is needed to determine whether the mixed dolphin groups become more entangled in mating. The Wild Dolphin Project, the team of Dr. Herzing, gets the scoop by collecting dolphin feces and analyzing the genetic material they contain to reveal the dolphins’ lineage.
Guido J. Parra, a behavioral ecologist at Flinders University who was not involved in either study, said it was valuable to investigate these interactions. An understanding of social ties could help reveal how animal groups may respond to environmental change and aid conservation. Researchers still have a lot to learn about the ecological factors that drive grouping, the role of individuals in shaping a social structure, and the costs and benefits of collaboration, said Dr. parra.
That will be important because different dolphin populations can be pushed together. In Bangladesh, for example, rising seas penetrated a land border and brought river dolphins into contact with another dolphin species in the ocean, said Dr. Resing.
“We don’t know exactly how species are doing,” she said.