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Scientists have shown that two neighbouring groups of a great ape called bonobos living in an overlapping habitat have group-specific hunting preferences, according to a new study published today in eLife.
The findings provide strong evidence that the behaviour of non-human animals is shaped as much by their culture as it is by their genetics or environment.
Culture, defined as group-specific behaviours acquired through social learning, is known to be an important selective influence in human evolution. However, less is known about its importance in other animals.
To study cultural differences, it is necessary to separate out social processes from other influences that could contribute to particular behaviours. For most territorial animals in the wild, this means researchers need to measure and account for differences in the ecology of the animals’ preferred habitats, which is a challenge. In this study, researchers investigated differences in the hunting behaviours of two different bonobo groups – Ekalakala and Kokoalongo – at the Kokolopori Bonobo Reserve in the Democratic Republic of Congo. Bonobos happily reside in neighbouring groups within the same habitat, providing a uniform experimental setting within which to study their behaviour.
“These two bonobo groups share an extensive home range overlap and have regular gene flow, which reduces the influence of ecological and genetic variables on the differences in prey preference within groups,” explains lead author Liran Samuni, Postdoctoral Fellow at the Department of Human Evolutionary Biology, Harvard University, Boston, US. “We tested whether variation in prey preferences is explained by environmental variables, such as seasonality and hunting locations, and social factors, such as the number of hunters and their group identity.”
Between August 2016 and January 2020, Samuni and the research team observed 59 successful captures of prey – including anomalure (rodents), duiker (antelopes) and species of squirrels. They found that Kokoalongo bonobos were more likely to capture duiker and squirrels, and less likely to capture anomalure species, compared with the Ekalakala. This same pattern of hunting persisted, even when the groups mingled together.
These hunting trends could not be accounted for by environmental factors: more than 80% of the bonobos’ hunts occurred in overlapping areas, and the use of specific hunt locations or seasonal variation in prey had no effect on the types of prey captured by the two groups. There was also no difference by size of the hunting group, the number of male or female bonobos in the group, or the presence of specialised hunters within the group.
“We found that bonobo groups that use overlapping home ranges and regularly socialise and forage together show group-specific prey preferences,” concludes senior author Martin Surbeck, Assistant Professor at the Department of Human Evolutionary Biology, Harvard University, Boston. “These group-specific patterns appear independent of genetic and ecological variation, seasonality, size of the hunting parties and how closely the parties stick together, providing a strong indication of culturally transmitted hunting techniques in some of our closest-living relatives.”
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