Common chimpanzee behaviours, like stripping the leaves from a twig and using it to fish for termites, are becoming more rare according to new research that suggests that human activity is wearing down chimpanzee culture.
Culture, in the animal sense, being the diversity of behaviour and the sharing of knowledge between individuals.
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A study published on Thursday in the journal Science revealed an 88 percent decline on average in the number of behaviours a chimpanzee will show when they’re living near areas with lots of people, or roads, or without forest cover.
Chimpanzees might be more cautious about cracking nuts loudly using stones, for example, for fear of attracting the attention of poachers. Similarly, declining chimpanzee numbers mean there are fewer individuals to show others how to, say, get water using moss.
“We weren’t surprised that the human impact was having a negative effect but we were surprised by the degree,” primate researcher Ammie Kalan told Motherboard over the phone.
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The findings are frighteningly robust. Researchers catalogued 31 different behaviours (such as making cushions out of leaves or cooling down in a nearby cave) in 144 social groups. The study spanned the entire geographic range of wild chimpanzees, from Guinea in Western Africa to Southern Sudan in the east and Angola in the south.
No matter how the scientists grouped the behaviours in their statistical analysis, the results were the same: human impact isn’t just linked with population declines, it’s also affecting how chimpanzees behave.
“It wasn’t just based on a single glance at the dataset, but it was a really strong pattern,” Kalan said.
Chimpanzee numbers have declined by more than 80 percent in the past quarter century partly because of the fragmentation of their forest habitat through agriculture and climate change. This means there are fewer of them to pass on behaviours.
Behavioural diversity could also be decreasing, the authors note, because climate change is limiting the availability of foods or plants they smash up or use to hunt for ants.
The researchers aren’t sure whether chimps spontaneously developing new behaviours can make up for the loss in behavioural diversity. They fear some yet-unobserved behaviours may be gone before any human ever gets to witness them.
Chimpanzees aren’t the only animals that could suffer from culture loss thanks to anthropogenic activity and climate change. Kalan said that any animal that’s socially intelligent and spreads ideas between generations could be at risk: orangutans, whales, dolphins, elephants, even song birds with special dialects.
The latest United Nations Environment Programme report recognizes the importance of behavioural diversity and says data collection on social groups should be included in conservation efforts, along with keeping animal numbers and genetic variability up, going forward.
Kalan and the other study authors suggest creating “cultural heritage sites” to try and preserve chimpanzee behaviours. These would be specific locations that are particularly important to chimpanzees for tool use or communication—a cave or group of stones, for example.
“If those places didn’t exist then those behaviours most likely would not continue. It really becomes part of the cultural heritage of that chimpanzee community,” Kalan explained.
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