Dolphins Learn Foraging Tricks From Each Other, Not Just From Mom

Jun 25, 2020
Originally published on June 26, 2020 8:11 am

Dolphins learn special foraging techniques from their mothers—and it's now clear that they can learn from their buddies as well. Take the clever trick that some dolphins use to catch fish by trapping them in seashells. It turns out that they learn this skill by watching their pals do the job.

The discovery, reported in the journal Current Biology, helps reveal how groups of wild animals can transmit learned behaviors and develop their own distinct cultures.

"Dolphins are indeed very clever animals. So it makes sense that they are able to learn from others," says Sonja Wild, a researcher at the University of Konstanz in Germany. She says young dolphins spend years in close association with their mothers and naturally tend to adopt their mothers' ways, but this study shows that "dolphins are not only capable, but also motivated to learn from their peers."

The bottlenose dolphins that live in Shark Bay, Western Australia, have been studied for decades, and scientists have identified over a thousand individuals by looking at the unique shape and markings of their dorsal fins. Researchers know what families the dolphins belong to, and keep track of their close associates. These dolphins use a variety ways of finding food—and not every dolphin uses every method.

Some dolphins, for examples, use sponges as tools. The dolphins break a conical sponge off the seafloor, and then wear it almost like a protective cap on their long snout, or beak. This apparently helps them probe into the rough sand of the rocky seafloor and search for buried prey.

Research done over a decade ago shows that this behavior gets passed down almost exclusively from mother to child. "So, at some point, one of the dolphins figured out how to use these sponges for foraging," says Wild. After that, it was passed on to her descendants through the maternal line.

Now, Wild and her colleagues have closely examined how dolphins learn another strategy for catching fish—one that involves using the empty shells of large sea snails.

A dolphin practicing shelling behavior, which involves chasing a fish into a shell and then carrying the shell to the surface to consume the fish.
Sonja Wild/Dolphin Innovation Project

A dolphin will chase a fish into one of these shells, says Wild, "and then they insert their beak into the shell, bring the whole thing up to the surface, and then shake it up above the water surface to drain the water out of the shell until the fish basically falls into their open mouth."

"It's a very remarkable behavior," says Wild. "Seeing it is really mind blowing."

When she and her colleagues tracked which dolphins used this so-called "shelling" technique, they figured out that "the shelling behavior doesn't spread between mother and offspring, but spreads between peers. So basically, dolphins that spend a lot of time with shelling individuals are more likely to learn that behavior themselves," says Wild.

Whether or not dolphins caught fish in this way didn't seem to be explained by how many shells were lying around their hunting area, nor whether a dolphin was genetically related to another dolphin that knew how to do it. The best explanation, she says, is that dolphins learned this method from a close associate.

Previously, it's been shown that humpback whales seem to learn hunting techniques from their peers in a similar way, she notes.

The new observations of wild dolphins learning from their peers is "exciting," says Diana Reiss, a dolphin cognition researcher at Hunter College, CUNY.

"It tells us about the source of some these behaviors," says Reiss. "Are they learning because they innovate individually on their own? They may. We can't discount that. Are they learning just from their mom? They may for certain kinds of behaviors. But in this particular behavior, it seems like they're not relying on just learning from mom when they're out there. They seem to be observing others, watching what they're doing and acquiring it from others in their social group."

Being able to learn from peers may help animal populations survive in a changing environment. Because while knowledge from previous generations has been tested by time, certain behaviors may become less useful if conditions change.

"In unstable environments that are changing, it's more beneficial to kind of look around and see what others are doing," says Wild, "and maybe adopt their behavioral innovations that may be more adaptive to the new environmental conditions."

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ARI SHAPIRO, HOST:

Wild dolphins forage for food in all kinds of creative ways. Now researchers have studied exactly how dolphins learn one unusual method for catching fish. And as NPR's Nell Greenfieldboyce reports, this is one trick that they don't learn from their mothers.

NELL GREENFIELDBOYCE, BYLINE: Young dolphins spend years with their mothers learning how to take care of themselves and find food.

SONJA WILD: Most of these foraging behaviors are learned and passed on from mother to offspring.

GREENFIELDBOYCE: Sonja Wild is a researcher at the University of Konstanz in Germany. She's studied dolphins at Shark Bay in Western Australia. Their scientists have spent decades following over a thousand individual dolphins. Some of these dolphins search for food with the help of tools like sponges.

WILD: Dolphins wear these conically shaped sponges on their beaks as kind of a protective glove from when they go dig into sand for buried prey.

GREENFIELDBOYCE: Previous work has revealed that dolphins will only use sponges in this way if their mothers do it. It looks like at some point, one female dolphin figured out this strategy. Since then, it's been passed down from mother to child. But recently, Wild and her colleagues got interested in another food-finding technique. This one involves the use of shells, big empty shells left behind by sea snails. Wild says a dolphin will chase a fish into one of these shells.

WILD: And then they insert their beak into the shell, bring the whole thing up to the surface and then shake up above the water surface to drain the water out of the shell until the fish basically falls into their open mouth.

GREENFIELDBOYCE: This method became a lot more popular with the dolphins about a decade ago. That's when a heat wave killed off a lot of sea snails and left a lot of empty shells lying around.

WILD: It's a very remarkable behavior also given the fact that dolphins need to do this with their beaks. They don't have any hands to use, so seeing it is really mind-blowing.

GREENFIELDBOYCE: Wild and her co-workers tracked how this behavior spread through the dolphin population, who was doing it first and who followed over time.

WILD: And we figured out that the shelling behavior doesn't spread between mother and offspring but spreads between peers. So basically, dolphins that spend a lot of time with shelling individuals are more likely to learn that behavior themselves.

GREENFIELDBOYCE: These findings appear in the journal Current Biology. Diana Reiss is a dolphin researcher at Hunter College in New York who wasn't part of the research team. She says this discovery is exciting because of what it tells us about social learning among wild dolphins.

DIANA REISS: When they're out there, they seem to be observing others, watching what they're doing and acquiring it from others in their social group.

GREENFIELDBOYCE: This is similar to what humans and great apes can do, and it could help dolphins survive in a changing environment. Wild points out that a mother-knows-best approach can make a lot of sense when conditions are stable.

WILD: Because the knowledge of those previous generations is tested and stable and adapted to the current environmental conditions.

GREENFIELDBOYCE: But when those conditions become unstable, there's real advantages to being able to follow a pal who's come up with a bright new idea.

Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.