In the crystal clear waters of Shark Bay in Western Australia, scientists have noticed bottlenose dolphins engaging in an unusual behavior: They guide fish into the empty shells of giant snails, bring the shells to the surface, and then shake them vigorously to dislodge the prey into their open mouths—like a person polishing off a bag of popcorn. That extra effort, known as “shelling,” gets them a guaranteed meal.
Because the dolphins (Tursiops aduncus) use the shells as a trap, this is the second known case of these marine mammals using tools. (The first was reported in 1997 when researchers found that bottlenose dolphins wear marine sponges like protective gloves over their beaks to forage for fish on the sea floor.) Now, researchers have shown that the dolphins of Shark Bay learn shelling from their friends. It’s the first time social learning involving a tool has been discovered in these mammals—and a rare example of such learning in the animal kingdom.
Scientists studying primate cultures have shown social learning is typically found in tolerant species—those animals that are able to peacefully accept others being nearby—with a broad variety of distinct foraging and other techniques that are passed along. For instance, chimpanzees can make twig tools for termite “fishing,” leaf sponges for collecting water, and pointed sticks for hunting bush babies.
Though scientists noticed the shelling behavior more than 10 years ago, it became more frequent following an unusual marine heat wave off Western Australia in 2011. The high temperatures roiled Shark Bay’s ecosystem, and many gastropods—including sea snails—are believed to have died.
“We think the dolphins took advantage of this die-off,” says Sonja Wild, a behavioral ecologist at the Max Planck Institute of Animal Behavior. The next season, she says, there was “an incredible increase” in shelling, which made it possible for her to tease out how young adult dolphins learn to do it.
During surveys on the bay between 2007 and 2018, Wild and her colleagues documented almost 5300 encounters with dolphin groups and identified more than 1000 individual dolphins. They also saw 19 dolphins, which came from three genetic lineages, engage in shelling 42 times (see video, above).
To find out how such a disparate group had learned the technique, the team turned to social network analysis, taking into account genetic relationships, environmental factors, and which animals the dolphins preferred to spend time with. By analyzing the data, they found shelling spreads horizontally within generations (that is, from friend to friend) rather than vertically between generations (from mother to calf), they report today in Current Biology.
“It’s a great study,” says Richard Connor, a behavioral ecologist and dolphin expert at the University of Massachusetts, Dartmouth, who was not involved in the work. “It adds another technique to the incredible range of specialized foraging tactics,” used by dolphins, killer, and sperm whales.
Wild says shelling starts among the adults. But the more time a young dolphin spends around an accomplished sheller, she says, “the more likely it is to learn” the technique—and pass it on to others later.
Still, because dolphin calves spend more than 30,000 hours with their mothers, it’s possible that some learned the trick from their moms, says Janet Mann, a dolphin expert at Georgetown University. It’s considered more cognitively demanding to learn a skill like shelling from an unrelated individual because both learner and demonstrator must be “socially tolerant,” especially while hunting.
But the findings, if true, are promising for dolphins facing changing environments. “Species—like certain bird families—whose members are more innovative … are better at colonizing new habitats,” Connor points out. It may be that the range and diversity of dolphin species similarly stem from this kind of flexibility, he says, including a talent for “learning how to forage” in new ways. “Obviously, it helps if you can also learn from your friends.”