A female chimpanzee takes a branch, strips its leaves and dexterously inserts the stick into a termite mound, batting away the hand of her infant as if to say ‘look, don’t touch’. Meanwhile, two males fish for algae with improvised fishing rods, leaning out over the water, scooping and eating.

Over the course of ten years and across the entire geographic range of chimpanzees, totalling 144 social groups, these behaviours, along with 29 others including nut cracking, honey extraction and the use of tools for hunting and digging, have been filmed and identified. The research was undertaken with the aim of determining whether human actions near chimp habitats, measured with reference to population density, infrastructure and land change, has an effect on chimps’ remarkable behavioural diversity.

The international research team responsible, led by Hjalmar Kühl and Ammie Kalan from the Max Planck Institute for Evolutionary Anthropology, has now compiled the data and the results are categorical. ‘The analysis revealed a strong and robust pattern,’ said Kalan. ‘Chimpanzees had reduced behavioural diversity at sites where human impact was high. On average, chimpanzee behavioural diversity was reduced by 88 per cent when human impact was highest compared to locations with the least human impact.’

The team has identified a number of potential reasons for the trend. It points to the fact that smaller, fragmented populations of chimps means fewer chances to store and share cultural traits (a phenomenon already studied and well-understood in humans), and that habitat degradation and resource depletion reduce opportunities for social learning. Observations also suggest that chimpanzees avoid conducting noisier behaviour, such as nut cracking, when near humans.

Slash and burn agricultural landscape [Image: Hjalmar S. Kühl]

For Kühl, this degradation in behavioural diversity poses the risk of lost opportunities, both for future scientific enlightenment and for conservation. ‘From a scientific perspective it would be very interesting to still have the opportunity in the future to understand how culture and cultural transmission works. When does culture emerge? Which ecological conditions are needed?’ he says. ‘But also, conservation has to motivate people and fascinate people. To only report that a species is declining is at some point not motivating any more.’

As a result of these concerns, Kühl and Kalan are now keen to see conservation efforts extended to include protection of behavioural diversity. Previous research has mostly focused on species decline and loss of genetic diversity in chimps, but this new project indicates that ensuring the survival of a species is not enough – behaviour is also at risk and needs protecting.

In particular, the team is calling for locations with exceptional sets of behaviours to be protected as ‘chimpanzee cultural heritage sites’, a system based on the UNESCO model for humans. ‘We cannot just protect the species, or the physical appearance of the species, we also have to protect their habitat so that they can show this behaviour,’ says Kühl. ‘In some cases chimpanzees survive, but it’s a totally different habitat such as an agricultural area. Then you still have the chimpanzees but they have lost all of their evolutionary behaviours because they don’t have any chance to practice.’

This was published in the May 2019 edition of Geographical magazine

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