Acquisition of a complex extractive technique by the immature chimpanzees of Loango National Park, Gabon

The relative importance of individual and social learning in acquiring complex technological skills in animals is debated, especially the influence of processes allowing high copying fidelity (namely, imitation and teaching). We investigated how immature wild chimpanzees, Pan troglodytes troglodytes, acquired the technique for extracting underground honey. This technique is interesting because (1) adults perform exploration, pounding and perforation in nonrandom but highly flexible action sequences to locate underground bee nests, (2) they have individual preferences for how to perforate the ground and (3) the nests are deeply buried and concealed, making success difficult to achieve. We analysed the behaviour of 16 immatures recorded by camera traps at 50 sites, and tested the influence of individual attributes (namely, age and sex) and maternal behaviour; we also tested whether mothers provided learning opportunities for their offspring. We found that, as they aged, immatures of both sexes progressively matched adults' behaviour in action sequences and observed their social models more continuously. Immature males used the most common grip type used by adults for perforating (namely, the coordinated use of hands and feet) progressively more as they aged, but no effect of maternal preferences was detected. Thus, the adult technique was probably acquired via a combination of physical maturation (i.e. increased body strength and motor coordination) and observational learning, although individual learning could not be completely ruled out. Finally, the proportion of time mothers spent inactive at bee nest sites was high when they were accompanied by young daughters and decreased as daughters aged, while the opposite pattern was found for sons. Mothers may thus stimulate learning by immatures by adjusting their behaviour according to their offspring's sex and age. Overall, we showed that immature chimpanzees acquired this complex tool use behaviour via a combination of social and nonsocial learning processes, including potential maternal stimulation.