Social networks and culture among dolphins

Recently published research in Nature Communications ‘Social networks reveal cultural behaviour in tool-using using dolphins‘ is exploring social networks of dolphins. In particular, it finds evidence for homophily on a learned skill which leads that there’s an exclusion and cultural contagion even among cetaceans.


Animal tool use is of inherent interest given its relationship to intelligence, innovation and cultural behaviour. Here we investigate whether Shark Bay bottlenose dolphins that use marine sponges as hunting tools (spongers) are culturally distinct from other dolphins in the population based on the criteria that sponging is both socially learned and distinguishes between groups. We use social network analysis to determine social preferences among 36 spongers and 69 non-spongers sampled over a 22-year period while controlling for location, sex and matrilineal relatedness. Homophily (the tendency to associate with similar others) based on tool-using status was evident in every analysis, although maternal kinship, sex and location also contributed to social preference. Female spongers were more cliquish and preferentially associated with other spongers over non-spongers. Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour.

Photo by Ewa Krzyszczyk;
For centuries, philosophers and scientists have debated whether cultural behaviour distinguishes Homo from all other taxa12. Whether non-human animals have at least rudimentary culture is contested, partly because scholars disagree on the definition of culture and/or what type of supporting evidence is needed2. To empirically investigate whether or not a given species has ‘culture,’ the term must be operationally defined. Regardless of discipline, scholars agree that some form of social learning is a prerequisite and that culture is a source of uniformity within groups and differences between groups3, but the consensus ends here. Social learning is defined as learning (behaviour matching) that is influenced by observation of, or interaction with another animal or its products45. Some definitions of culture require more complex cognitive social learning mechanisms, such as pedagogy, theory of mind and imitation67. In most animal culture studies, examination of behavioural variation within and between groups is fairly straightforward as animals are either geographically or socially segregated2. However, ‘group’ is not easily defined in all animal societies. Like humans, Shark Bay bottlenose dolphins live in an open community, characterized by high fission–fusion dynamics where members maintain long-term preferential bonds, but associations are temporally and spatially variable across minutes, days and years8. The question is therefore whether dolphins that use sponge tools (spongers) to extract prey910 exhibit homophily (the tendency to associate with similar others), based on this socially learned foraging tactic1011.

In Shark Bay, Australia, a subset of the community of Indo-Pacific bottlenose dolphins (Tursiops sp.) procure and wear basket sponges on their beaks while lightly scouring the seafloor for prey in deep (8–13 m) channels (Fig. 1)9101112. Sponging is the best-documented case of tool use by wild cetaceans and is unique among wildlife in that only a small subset of the population uses tools. This exceptional case of tool-use heterogeneity allows us to test for preferential affiliation based on tool-use. To date, 55 dolphins have been documented habitually using sponges in the eastern gulf of Shark Bay12, although sponging also occurs in the western gulf13. Only calves of spongers become spongers (24 offspring to date), but 8 offspring of spongers never adopted sponging. Sponging is a solitary activity, but calves accompany their mothers during sponging and vertical social learning is strongly implicated as the primary mechanism of transmission101114, consistent with mitochondrial DNA analysis1315

Full paper link.