When hunger strikes, dolphins don’t waste time.
In Shark Bay, Western Australia, these swimming mammals have devised devious tactics to catch slippery prey. In a trick, dolphins chase fish in empty seashells, then transport the shells to the ocean surface, where they use their beaks to push prey into their mouths.
This behavior, called bombardment or shell, 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 for Animal Behavior in Germany. Dr. Wild first witnessed the shelling in 2013 and compares the behavior of scooping lost crumbs out of an almost empty bag of potato chips. “It is really remarkable when suddenly there is a giant shell appearing next to the boat, being shaken by a dolphin.”
Most dolphins acquire skills from their mothers with tool skills, and one could assume that the art of the shell would also be inherited. But Dr. Wild and her colleagues have found that gentle swimmers can also acquire this behavior by mimicking the movements of unrelated partners. The study, published Thursday in Current Biology, adds to growing evidence that toothed whales like dolphins can alternate between learning both inside and outside their nuclear families, a talent generally associated with orangutans, chimpanzees, and humans. .
Dolphins were already suspected of learning feeding strategies from their peers, and are even anecdotally reported, said Eric Angel Ramos, a dolphin behavior researcher at New York City University 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 has ever done it that way,” Ramos said.
A team led by Simon Allen of the University of Bristol in England and Michael Krützen of the University of Zurich began surveying Shark Bay bottlenose dolphins in 2007. In the 11 years that followed, they accumulated genetic data and behavior in more than 1,000 dolphins, identifying 19 individuals that bombed a total of 42 times.
That’s not much, Dr. Wild said. The part of the bombardment that is visible to researchers aboard a boat, the displacement of the shell on the ocean surface, is rapid, often lasting only a few seconds, and the researchers are probably not counting how often it occurs. But the tactic probably isn’t implemented frequently, and certainly not all dolphins do, he said.
Still, the shells in the studio seemed to have something in common: each other. Although the rattling dolphins were not closely related, a computer analysis showed that they belonged to many of the same social networks.
“The more time two people spend together, the more likely they are to copy each other’s behavior,” said Dr. Wild.
That distinguishes dolphin bombardment antics from another skill, the sponge, in which animals place sea sponges under their noses to protect them as they feed on ocean sand. Previous research shows that this trade is transmitted through a classic “mom knows best” strategy. “If you’re alive, you know your mother has done something right,” said Dr. Wild.
Still, sometimes it’s worth looking for a new talent outside of your family. After a severe heat wave hit Shark Bay in 2011, causing widespread deaths in local marine life, the data shows an increase in the shell, Dr. Wild said. In the wake of the catastrophe, studying the bombings of their peers may have helped some dolphins find more food.
Much is unknown about conching. Understanding any complex skill requires patience, practice, and often luck, and the dolphin shell probably can’t be attributed to peer-to-peer imitation, said Janet Mann, a dolphin researcher at Georgetown University who was not involved in studying . Some may gain bombardment skills from mom. The availability of sea shells on the seafloor could even inspire some dolphins to innovate behavior for themselves.
“We have barely scratched the surface of the water” understanding the behavior of dolphins, said Dr. Mann.
Still, Mr. Ramos considers the study “groundbreaking” for its rigor and treasure of genetic and behavioral observations. “This brings dolphins into the primate and human fold” even more than previously thought, he said.
