Social networks reveal cultural behaviour in tool-using dolphins

Abstract

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.

If at first you don't succeed… Studies of ontogeny shed light on the cognitive demands of habitual tool use

“…To date there is no evidence for cognitive specializations in tool-using species compared to non-tool-using relatives (see [93]), but there has been little exploration of differences in domain-general executive functions such as inhibition and attention between species. Third, ecological-and social-learning opportunities during the early stages of development appear to play an important role in determining later skill levels and thus individual and geographical variation [10,61]. Variation among adults moreover indicates that tool performance is not simply a matter of brain maturation but also (social-) learning opportunities.…”

“…Van Schaik et al [97] demonstrated a strong relationship between tool-use competence and mean female party size in orangutans. An analysis of social networks among tool-using dolphins, showed that after weaning, spongers preferred to associate with other spongers [61], which may be crucial for them to be able to find the best sites for tools and prey. Such social-learning opportunities may also affect tool repertoires on a wider scale (i.e.…”

“…Given that individual variation in competence often varies with learning opportunity (with some immatures performing even better than some adults, see §4), we suggest that opportunities for learning, not maturation, is the primary limiting factor. Age might even constrain learning ability if a sensitive period of exposure has passed [10,61].…”

‘Captivity bias’ in animal tool use and its implications for the evolution of hominin technology

“…The principle is not restricted to the human lineage [43], and wild orangutans and chimpanzees have been found to display increased complexity, success and frequency in tool use in increasingly social and higher population density settings [44][45][46]. Further, wild meerkats [47], captive cockatoos [35] and wild female dolphins also show that social effects can enhance tool use [48]. These examples suggest that both increased population size and density, where these promote increased contact between individuals, can facilitate the retention and spread of technological innovations and subsequently increase diversity in a species' tool-use repertoire.…”

Maternal and Alloparental Discipline in Atlantic Spotted Dolphins (Stenalla frontalis) in the Bahamas

“…Spotted dolphin calves are age three and under (Herzing, 1997), and are dependent on their mothers for survival and integration into their social group. This is the case for many social mammals including other dolphin species and primates (Maestripieri, 2011;Mann, Stanton, Patterson, Bienenstock, & Singh, 2012;Rendell & Whitehead, 2001). Calves are also reported to spend the majority of their time with their mothers for the first three years of life (Herzing & Brunnick, 1997), until subsequent offspring are born.…”