Shark Bay Indo-Pacific bottlenose dolphins in Western Australia have an unusual way of obtaining food.
They divide the fish into a large empty marine gastropod shell. They then bring the shell and the captured fish to the surface, and shake it upside down. Sip! go to the fish, straight to the dolphin belly.
It’s called bombardment, only the second documented use of tools among dolphins, and the first in which dolphins have been seen learning from their friends, just like great apes.
“This is an important milestone,” said evolutionary biologist Michael Krützen of the University of Zurich in Switzerland.
“It shows that the cultural behavior of dolphins and other toothed whales is much more similar to the behavior of great apes, including humans, than previously thought.”
The Dolphins (Tursiops aduncus) were first observed with tools more than 20 years ago, sliding sea sponges over their beaks as a thimble to protect them while feeding. This behavior was called a sponge, and it allows dolphins to access food in channels of deeper water than dolphins without a sponge.
The sponge is adopted in matrilineal lines, a skill passed down from mothers to daughters, a type of learning called vertical transmission.
But there is another type of learning, the horizontal social transition, in which individuals acquire skills from their social partners: their friends. This is most strongly seen in species with broad cultural repertoires, such as great apes.
There are similarities between dolphin and great ape societies that have led scientists to believe that dolphins should be able to learn horizontally.
“Despite their divergent evolutionary histories and the fact that they occupy such different environments: both dolphins and great apes are long-lived, big-brained mammals with high capacities for innovation and cultural transmission of behaviors.” Krützen said.
Previous studies on whether dolphins can learn from their friends have been promising, but not conclusive. Now, a team of researchers led by behavioral ecologist Sonja Wild of the University of Konstanz in Germany has finally identified him.
Their data comes from more than a decade of observations. Between 2007 and 2018, researchers documented more than 1,000 individual dolphins in nearly 5,300 animal encounters.
Between those encounters, the bombardment behavior was observed in 19 individuals from three different genetic lineages, on 42 separate occasions.
That’s a relatively low number compared to the total number of encounters, but it was enough to run an analysis to determine how the behavior was learned.
They used genetic, behavioral, and environmental data to model possible routes of transmission, and found that the bombardment probably spread among friends, rather than from parents.
“These results were quite surprising, as dolphins tend to be conservative, with the young following a” mothering “strategy to learn feeding behaviors,” said Wild.
“However, our results show that dolphins are definitely capable and, in the case of shelling, they are also motivated to learn new feeding tactics outside of the mother-calf bond. This opens the door to a new understanding of how dolphins they can adapt to behavior in changing environments, as learning from peers allows rapid spread of novel behavior among populations. “
For example, in 2011, a large ocean heat wave devastated Shark Bay’s seagrass habitat, where dolphins forage for food. This resulted in the deaths of the fish and invertebrates that live in the giant shells that the dolphins use for their fishing, and then, there was an immediate increase in the behavior of the dolphin shelling.
It is possible, the researchers said, that both the decline in fish and the increase in shells could have played a role in this increase.
“While we can only speculate whether this depletion of prey gave dolphins an impetus to adopt a new search behavior from their associates,” said Wild, “it seems quite possible that a large number of dead giant gastropod shells may have increased. learning opportunities for bombing behavior. “
The research has been published in Current biology.