Because the dolphins (Tursiops aduncus) use the shells as a trap, this is the second known case of these marine mammals that use tools. (The first was reported in 1997 when researchers discovered that bottlenose dolphins use sea sponges as protective gloves over their beaks to search for fish at the bottom of the sea.) Now, researchers have shown that Shark Bay dolphins learn bombardment from their friends. It is the first time that 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 that social learning is generally found in tolerant species, those animals that can peacefully accept others in close proximity, with a wide variety of different feeding techniques and other techniques that are passed on. For example, chimpanzees can make twig tools to “catch” termites, leaf sponges to collect water, and pointy sticks to hunt babies from shrubs.
Although scientists noted the behavior of the bombings more than 10 years ago, it became more frequent after an unusual ocean heatwave in Western Australia in 2011. High temperatures shook the Shark Bay ecosystem, and many gastropods are believed to have including sea snails, died.
"We believe the dolphins took advantage of this death," says Sonja Wild, a behavioral ecologist at the Max Planck Institute for Animal Behavior. The next season, he says, there was "an incredible increase" in the shelling, allowing him to discover how young adult dolphins learn to do so.
During surveys in the bay between 2007 and 2018, Wild and his colleagues documented nearly 5,300 encounters with groups of dolphins and identified more than 1,000 individual dolphins. They also saw 19 dolphins, which came from three genetic lineages, participate in the bombardment 42 times (see video, above).
To discover how such a disparate group had learned the technique, the team turned to social media analysis, taking into account genetic relationships, environmental factors, and which animals the dolphins preferred to spend time with. Analyzing the data, they found that the bombings spread horizontally across generations (i.e., friend to friend) rather than vertically across generations (from mother to offspring), 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. "Add another technique to the incredible range of specialized feeding tactics," used by dolphins, killers, and sperm whales.
Wild says the shelling begins among adults. But the more time a young dolphin spends around an accomplished shell, he says, "the more likely he is to learn" the technique and pass it on to others later.
Still, because calves spend more than 30,000 hours with their mothers, some may have learned the trick from their mothers, says Janet Mann, a dolphin expert at Georgetown University. Learning a skill like bombing from an unrelated individual is considered more cognitively demanding because both the learner and the demonstrator must be "socially tolerant", especially while hunting.
But the findings, if true, hold promise for dolphins facing changing environments. "Species, like certain families of birds, whose members are more innovative ... are better at colonizing new habitats," says Connor. It may be that the range and diversity of dolphin species similarly derive from this type of flexibility, he says, including a talent for "learning to forage" in new ways. "Obviously, it helps if you can also learn from your friends."