When hunger strikes, dolphins don’t mess around.
In Shark Bay, Western Australia, these swimming mammals have devised devious tactics to snare slippery prey. In one trick, dolphins chase fish into empty seashells, then chauffeur the shells to the ocean surface, where they use their beaks to jostle the prey into their mouths.
This behavior, called shelling or conching, is rarely documented by scientists.
“You never know when it’s going to happen,” said Sonja Wild, a behavioral ecologist at the Max Planck Institute of Animal Behavior in Germany. Dr. Wild first witnessed shelling in 2013 and compares the behavior to dislodging stray crumbs out of a near-empty bag of chips. “It’s really remarkable when all of a sudden there’s a giant shell popping up by the boat, being shaken by a dolphin.”
Most dolphins pick up tool-savvy skills from their mothers, and one might assume that the craft of conching would be inherited, too. But Dr. Wild and her colleagues have discovered that the smooth swimmers may also acquire this behavior by mimicking the movements of unrelated peers. The study, published Thursday in Current Biology, adds to a growing body of evidence that toothed whales like dolphins can toggle between learning from both within and outside of their nuclear families, a talent usually associated with orangutans, chimpanzees and us humans.
That dolphins can learn feeding strategies from their peers has been strongly suspected before, and even anecdotally reported, said Eric Angel Ramos, a dolphin behavior researcher at City University of New York who was not involved in the study. But actually quantifying what drives the phenomenon is “very, very challenging,” in part because it requires years of detailed data on large numbers of individual animals.
“No one’s ever done it like this,” Mr. Ramos said.
A team led by Simon Allen, of the University of Bristol in England, and Michael Krützen, of the University of Zurich, first started surveying Shark Bay’s bottlenose dolphins in 2007. In the 11 years that followed, they amassed genetic and behavioral data on more than 1,000 dolphins, identifying 19 individuals that shelled a total of 42 times.
That’s not much, Dr. Wild said. The part of shelling that’s visible to boat-borne researchers — the shell-shimmying at the ocean surface — is fast, often lasting just a few seconds, and researchers are probably undercounting how often it occurs. But the tactic probably isn’t deployed frequently, and certainly not all dolphins do it, she said.
Still, the shellers in the study seemed to have something in common: each other. Though the conch-rattling dolphins weren’t very closely related, a computational analysis showed they belonged to many of the same social networks.
“The more time two individuals spend together, the more likely they are to copy behavior from one another,” Dr. Wild said.
That distinguishes dolphins’ shelling shenanigans from another skill, sponging, in which the animals fit marine sponges to their noses to protect them as they forage in rough ocean floor sand. Earlier research shows this craft is passed down through a classic “mom knows best” strategy. “If you’re alive, you know your mother has done something right,” Dr. Wild said.
Still, sometimes it pays to look outside your family for a new talent. After a serious heat wave struck Shark Bay in 2011, prompting widespread die-offs in local marine life, the data shows an uptick in conching, Dr. Wild said. In the wake of catastrophe, studying shelling from peers might have helped some dolphins find more food.
Much about conching remains unknown. Getting the hang of any complex skill requires patience, practice and, oftentimes, luck — and dolphins’ conching probably can’t be chalked up purely to peer imitation, said Janet Mann, a dolphin researcher at Georgetown University who wasn’t involved in the study. Some might get shelling skills from mom. The availability of seashells on the seafloor could even inspire a few dolphins to innovate the behavior on their own.
“We’ve barely scratched the water’s surface on” understanding dolphin behavior, Dr. Mann said.
Still, Mr. Ramos considers the study “groundbreaking” for its rigor and treasure trove of behavioral and genetic observations. “This brings dolphins into the fold of primates and humans” even more than previously thought, he said.