In Shark Bay, Australia, bottlenose dolphins that aren’t related have been observed teaching each other a new way to use a tool, a behavior that until now scientists have found only in humans and other great apes.
It’s also the first known example of dolphins transmitting such knowledge within the same generation, rather than between generations. That’s significant, the authors say, because such social learning between peers is rare in nature.
In a practice called shelling, dolphins will chase fish into abandoned giant snail shells on the seafloor, then bring the shells to the surface shake them with their noses, draining the water and catching the fish that fall out.
Dolphin mothers generally teach their young how to hunt: Shark Bay dolphin moms, for instance, teach their offspring sponging, another form of tool use in which dolphins put sponges on their beaks to protect them while foraging among rocks. (Explore our interactive of the tools animals use.).
"The fact that shelling is socially transmitted among dolphin peers rather than between mother and offspring sets an important milestone, and highlights similarities with certain primates, who also rely on both vertical and horizontal learning of foraging behavior," senior study author Michael Krützen, an anthropologist at the University of Zurich, said in a press statement.
Though dolphins and great apes have very different evolutionary histories and habitats, they’re both long-lived, large-brained mammals with tremendous capacity for innovation and culture, Krützen says.
Maggie Stanton, a psychologist at Franklin & Marshall College in Pennsylvania, who has studied Shark Bay dolphins and chimpanzees at Tanzania’s Gombe Stream National Park, agrees. One chimp family in Gombe, she notes, may have learned how to use tools to extract ants from a female chimp that joined the community.
Cracking a mystery
In 2007, Krützen launched a study of Shark Bay’s dolphins, identifying more than a thousand individual dolphins over 11 years. During this time, scientists observed shelling 42 times among 19 dolphins. Half of these events occurred after a marine heatwave in 2011, which may have caused a die-off among giant sea snails, leading to more discarded shells on the seafloor. (Read about a new species of dolphin discovered in Australia.)
Because of the length of their study, scientists had intimate knowledge of the individual dolphins’ family histories, ages, sexes, and behavior, making it easier for them to study the 19 dolphins that practiced shelling. For instance, they observed that the dolphins that practice shelling hang out with other shellers, so it’s likely that they copy from those they spend time with, says study lead author Sonja Wild, a postdoctoral researcher at the University of Konstanz in Germany.
These shelling dolphins were always within the same generation, according to the study, published June 25 in the journal Current Biology.
The team knew that environmental factors—specifically, whether shelling dolphins did so simply because they lived in a shell-rich area—could explain this peer-to-peer transmission. A genetic trait among a family group was another possible reason.
So the researchers combined their data on the dolphin sightings, as well as genetic and environmental data, into a computer model that proposed various ways shelling could be transmitted between dolphins. The model that supported horizontal transmission was the strongest outcome, according to the study.
Although 42 observations is a small data set, the scientists add, it’s likely the behavior is actually common; it only lasts a few seconds, making it harder for people to spot from a boat.
Dolphins, like chimpanzees, live in loosely formed communities, in which individuals move freely from group to group. That means they’re more exposed to different animals—and behaviors—on a regular basis than, say, a baboon troop, which has a fixed group of members.
It’s similar to humans, in that “sometimes you’re with this group of friends and sometimes you’re with this group of your family, and it changes throughout the day,” she says. (Read how dolphins have bold and shy personalities, like us.)
She adds the new research is notable in its scope, particularly because it took into account those environmental and genetic reasons for shelling.
“It’s invaluable data to have these long-term field studies—you can’t get these data any other way."