Dolphins can learn from peers how to use shells as tools

For some bottlenose dolphins, finding a meal may be about who you know.

Dolphins often learn how to hunt from their mothers. But when it comes to at least one foraging trick, Indo-Pacific bottlenose dolphins in Western Australia’s Shark Bay pick up the behavior from their peers, researchers argue in a report published online June 25 in Current Biology.

While previous studies have suggested that dolphins learn from peers, this study is the first to quantify the importance of social networks over other factors, says Sonja Wild, a behavioral ecologist at the University of Konstanz in Germany.

Cetaceans — dolphins, whales and porpoises — are known for using clever strategies to round up meals. Humpback whales (Megaptera novaeangliae) off Alaska sometimes use their fins and circular bubble nets to catch fish (SN: 10/15/19). At Shark Bay, Indo-Pacific bottlenose dolphins (Tursiops aduncus) use sea sponges to protect their beaks while rooting for food on the seafloor, a strategy the animals learn from their mothers (SN: 6/8/05).

These Shark Bay dolphins also use a more unusual tool-based foraging method called shelling.  A dolphin will trap underwater prey in a large sea snail shell, poke its beak into the shell’s opening, lift the shell above the water’s surface and shake the contents into its mouth.

“It is pretty mind-blowing,” says Wild, who studied these dolphins as a graduate student at the University of Leeds in England. This brief behavior appears to be rare: From 2007 to 2018, Wild and colleagues documented 42 shelling events by 19 individual dolphins out of 5,278 dolphin group encounters in the western gulf of Shark Bay.

The researchers analyzed the behavior of 310 dolphins, including 15 shellers, that had been seen at least 11 times. The dolphins’ network of social interactions explained shelling’s spread better than other factors, including genetic relatedness and the amount of environmental overlap between dolphins. Wild likens the proliferation of this behavior to the spread of a virus. “Just by spending time with each other, [dolphins] are more likely to transmit those behaviors,” she says. The researchers estimate that 57 percent of the dolphins that shell learned the skill via social transmission, rather than on their own.

But the researchers may be premature in dismissing environmental and maternal factors, says Janet Mann, a biologist at Georgetown University in Washington, D.C., who also studies dolphin behavior at Shark Bay. The environment affects where shelling can occur. “Those shells are found in particular habitats, and animals who overlap in those habitats would have access to those shells, but also bump into each other more often,” she says. A dolphin’s shelling behavior could also have been influenced during the tens of thousands of hours the animal spent as a youngster watching its mother.

“Dolphins are smart: They watch each other and see what others do,” she says.