Foraging Friends

Study reveals a surprising reason dolphin friendship is key to survival

Dolphin social networks have an important mission: teaching each other how to forage effectively.

Dolphins' uncanny intelligence allows for some creative behavior when it comes to mating, gift-giving, and foraging.

Now, researchers have a better idea of how they learn some of their food-finding tricks: Dolphins rely on social networks of their peers to learn foraging behavior.

This discovery was published Thursday in the journal Current Biology.

These findings challenge previous assumptions about how those techniques are shared: Studying bottlenose dolphins, Tursiops aduncus, in Shark Bay, Australia, researchers found that a key tactic — called "shelling" — is taught peer-to-peer among dolphins. This is not unlike the social learning seen in chimpanzees and other primates.

When shelling, dolphins chase their prey — usually a fish — into empty snail shells, trapping them. Then, they stick their noses into the shell, tip it upward above the water, and shake their dinner loose.

In 2005, researchers in Shark Bay found evidence of dolphin moms teaching these foraging tricks. They called this custom of passing down foraging strategies through the maternal lineage vertical social learning.

This new study is the first quantitative evidence of dolphin foraging learned from peers, lead author Sonja Wild tells Inverse.

"This is surprising, as dolphins and other toothed whales tend to follow a do-as-mother-does strategy for learning foraging behavior," says Wild, a postdoctoral researcher at the University of Konstanz.

"We show for the first time that dolphins are not only capable, but in the case of shelling also motivated, to learn foraging behavior outside of the mother-calf bond."

Dolphin foraging by shelling.

The findings are exciting for two main reasons, Wild explains.

First, they provide yet another similarity between dolphins and great apes. Both seem to rely on learning foraging within their own generations, these findings suggest. Previous research has indicated that dolphins' intelligence is probably comparable to monkeys' — the only thing they're missing is thumbs.

The study also reveals a knack for environmental adaptation in dolphins. When the environment changes, some behaviors may be rendered inefficient or obsolete. Learning from others allows dolphins to speedily spread new ideas, teaching one another new behaviors to help them survive.

"So it has been suggested that species with the capacity to learn from peers may be better able to cope with environmental changes," Wild says.

Dolphin shelling.Sonja Wild

Dolphin data — The new study is based on long-term data from the Dolphin Innovation Project, which focuses on social dynamics in Shark Bay dolphins.

The data, which includes more than a thousand individual dolphins, allowed researchers to map out social networks of dolphins to study how they are connected.

"Social networks can be built based on association strengths among individuals simply by tracking how much time dolphins spend with each other," Wild explains.

Wild's team used social network analysis to track the spread of shelling behavior through the dolphin population. They observed that shelling followed along with the same connections they established based on time spent together.

Other foraging behaviors — using sponges as tools, intentional beaching — are among the "remarkable variety" of techniques dolphins in Shark Bay use, Wild says.

"Shelling adds to this remarkable catalog of foraging behavior and represents only the second reported case of foraging tool use in dolphins — with the first one being the sponge tool use," Wild says.

Abstract: Cultural behavior, which transmitted among conspecifics through social learning [1], is found across various taxa [2–6]. Vertical social transmission from parent to offspring [7] is thought to be adaptive because of the parental generation being more skilled than maturing individuals. It is found throughout the animal kingdom, particularly in species with prolonged parental care, e.g., [8, 9]. Social learning can also occur among members of the same generation [4, 10, 11] or between older, non-parental individuals and younger generations [7] via horizontal or oblique transmission, respectively. Extensive work on primate culture has shown that horizontal transmission of foraging behavior is biased toward species with broad cultural repertoires [12] and those with increased levels of social tolerance [13, 14], such as great apes. Vertical social transmission has been established as the primary transmission mechanism of foraging behaviors in the Indo-Pacific bottlenose dolphin (Tursiops aduncus) population of Shark Bay, Western Australia [6, 9, 15, 16]. Here, we investigated the spread of another foraging strategy, ‘‘shelling’’ [17], whereby some dolphins in this population feed on prey trapped inside large marine gastropod shells. Using a multi-network version of ‘‘network-based diffusion analysis’’ (NBDA), we show that shelling behavior spreads primarily through non-vertical social transmission. By statistically accounting for both environmental and genetic influences, our findings thus represent the first evidence of non-vertical transmission of a foraging tactic in toothed whales. This research suggests there are multiple transmission pathways of foraging behaviors in dolphins, highlighting the similarities between cetaceans and great apes in the nature of the transmission of cultural behaviors.
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