Indian Ocean bottlenose dolphins (Tursiops aduncus) are not only capable of learning new ways to catch prey, but they are also motivated to learn from their peers, not just from their mothers, according to a new study published in the journal Current Biology.
This is a dolphin ‘shelling.’ Image credit: Sonja Wild / Dolphin Innovation Project.
“Our study shows that the foraging behavior ‘shelling’ spreads through social learning among close associates,” said Dr. Sonja Wild, a researcher at the University of Leeds.
“This is surprising, as dolphins and other toothed whales tend to follow a ‘do-as-mother-does’ strategy for learning foraging behavior.”
Dr. Wild and colleagues investigated the spread of ‘shelling,’ a tactic used by some bottlenose dolphins when prey hides inside large empty shells of giant sea snails found in Shark Bay, Western Australia.
The dolphins use their beaks to bring these shells to the surface and then shake the trapped food into their mouths — like the last few crisps at the bottom of a packet.
This foraging behavior represents only the second reported case of tool use in dolphins. The dolphins of Shark Bay are also known to use marine sponges as foraging tools to help them catch prey.
“During shelling, dolphins chase their prey — usually a fish — into empty shells of giant gastropods, insert their beak into the shell, bring it to the water surface and then shake it about to drain the water out of the shell, so that the fish falls into their open mouth,” Dr. Wild said.
During boat-based surveys in the western gulf of Shark Bay between 2007 and 2018, the researchers identified 1,035 different individuals of Indo-Pacific bottlenose dolphins from 5,278 encounters and documented a total of 42 shelling events.
“There are surely more shellers’ in the population than we saw, since the whole event may only take a few seconds and could easily be missed,” they said.
“The question then was: how had this new way of foraging spread from one dolphin to the next?”
To find out, the scientists used social network analysis, taking into account the social network, genetic relationships, and environmental factors.
Their analysis concluded that the shelling behavior spreads socially primarily within — rather than between — generations, providing the first evidence that dolphins are also capable of learning from their peers, not just their mothers.
“The fact that shelling is socially transmitted among associates, rather than between mother and offspring, highlights the similarities between cetaceans and great apes in the way cultural behaviors are passed on,” said Professor Michael Krützen, director of the Department of Anthropology at the University of Zurich.
“Indeed, despite having divergent evolutionary histories and occupying different environments, there are striking similarities between cetaceans and great apes: both are long-lived, large-brained mammals with high capacities for innovation and cultural transmission of behaviors.”
The team also noted that not all shelling dolphins seem to engage in the behavior at the same frequency.
“Some dolphins use shells quite regularly during foraging, while others have only ever been seen with a shell once. So, while there may be other explanations, it’s possible that some dolphins have mastered the skill more than others,” Dr. Wild said.
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Sonja Wild et al. Integrating Genetic, Environmental, and Social Networks to Reveal Transmission Pathways of a Dolphin Foraging Innovation. Current Biology, published online June 25, 2020; doi: 10.1016/j.cub.2020.05.069
