Western chimpanzee (Pan troglodytes versus) honey dipping

In 1960, Jane Goodall set up camp with her mother Vanne on the eastern shore of Lake Tanganyika. The chimpanzees she had been sent to study promptly fled, and for several months Goodall caught only glimpses of them from afar, or heard their distant calls echoing through the forest. Her predicament is familiar to anyone trying to study wild animals that are wary of human incursion, a state that biologists term ‘unhabituated’.

Goodall was eventually able to habituate the Gombe chimpanzees to her presence by offering bananas at her camp, and through her tenacity at following the animals to prove that she was no threat to them. Once habituated, the animals tolerated her close presence and allowed her to make the discoveries of tool-use, meat-eating and more that made her name as a scientist. But even today every new chimpanzee field site faces the same problem, and starts from scratch.

Here’s Jane with David Greybeard and his bananas, in a photo taken by Vanne in 1963:

Luckily, we now have a range of options for studying unhabituated animals that Jane and her mother lacked. These include remotely triggered cameras, and an approach that my colleagues and I developed called primate archaeology, in which the tools and traces left behind by foraging animals are collected and recorded just as we would for the material at a human archaeological site. Today’s post looks at the work of Joana Bessa from the University of Oxford, who used these techniques to show just how much information we can now get from unhabituated groups.

The honey trap

We’re in the west African nation of Guinea-Bissau, an independent country once part of the Mali empire and later colonised by the Portuguese. More specifically we’re in Cantanhez National Park, in the south of the country close to the border with Guinea. The park is home to around a dozen chimpanzee communities, ranging in size from 35 to 60 individuals each, although these are estimates (again, unhabituated animals don’t make things easy).

Bessa’s interest was in a high-energy food source preferred by chimpanzees across Africa: honey. Some groups of chimpanzees eat honey by hand, directly from the nest, while others—including some of the Gombe chimpanzees—are known to use tools to scrape and dip for this sweet treat. Initial surveys through the forest suggested that the Cantanhez animals fell into the first category, with traces of honey-eating showing up in analysis of chimpanzee poo but no sign of tools.

As often happens in wild animal research, however, a longer look showed that there was more going on. Bessa worked continuously in the field with the Cantanhez chimpanzees from February 2017 to December 2018, walking more than 1000 km of set trails and directly encountering the animals over 4200 times. She also placed remote camera traps covering the home range of four different chimpanzee communities in the National Park.

This extended effort paid off. Here’s footage from one of the traps, in which a chimpanzee inserts a manufactured tool into the opening of a stingless bee (Meliponula sp.) hive:

The Cantanhez chimpanzees also ate honey without using tools, shown by teeth marks in wax and honeycomb pieces found by Bessa’s team. The camera traps captured this activity too—and the daring required to face down the angry insects:

camera traps captured chimpanzees on three separate occasions in Caiquene-Cadique raiding a natural HB hive, by inserting their hands deep inside a tree trunk. As soon as these chimpanzees removed their hands from the active hive, swarms of bees emerged, and the chimpanzees ran off holding honeycomb.

However, two of the four communities studied by Bessa were clearly heavily invested in making and using stick tools to get honey. In total, 204 stick tools were found at 70 different nest sites, with all but one of those tools coming from either the Madina or Cambeque groups (that’s a Cambeque group chimpanzee in the video above).

In every case the tools were found at or scattered near the entrance to a bee hive. Most often the sticks came from the same tree that the bees were using, or from another tree within a few metres of the tool-use site, or atelier.

The probes were made from living twigs, and they showed various signs of modification by the chimpanzees. As you can see in the image below, the ends of the tools were regularly frayed, blunt, or split, and more than half of the tools had recognisable honey residue on one of the ends. In part E of the image, the team presents tools that might have had each of their ends used for different purposes, with one end frayed and the other blunt from forceful use:

Fraying happens both when a tool is inserted into the narrow nest opening, and possibly also as part of the tool-making process itself, so more fraying might be expected for tools that are used repeatedly at a site. Further clues that the nests were seeing multiple raids came from a more archaeological approach. Bessa tracked the ways that sticks in the forest decay once detached from a tree, and then compared that data to tools found around the nests. She proved that tools could be grouped into sets that were used on different days at the same site.

The damage to the tools even allowed Bessa and her team to classify them into three main groups based on their role in honey-gathering:

The first are exploratory probes, where very little modification is present. On some occasions (as confirmed by camera trap footage) chimpanzees simply procure a small twig, remove some side branches with leaves, and use it in a delicate motion to test if there is any honey present in the hive to collect. The second are pounding tools, where one or both tool ends present blunt or mashed ends, suggesting a pounding motion, possibly to break or separate the hard wax in the hive. Finally, the third type represent extraction tools—these have brush ends that are either a by-product of use or a deliberate modification.

Chimpanzees in central Africa have been found using different tools one after the other to forage for insects, so it is possible that the same pattern of behaviour is happening at Cantanhez. However, this is one behavioural reconstruction where direct observations of the wary, unhabituated animals would greatly reduce the amount of guesswork involved.

In case you were wondering, people living in the same area also gather honey, but they do so using machetes to enlarge the access hole and cut twigs for probing. They therefore leave distinct damage that cannot be confused with that caused by chimpanzees. Just as happened in Europe when Homo sapiens and Neanderthals hunted alongside each other, the forests of Cantanhez have two large primates going after the same resource using similar technology, albeit with archaeologically detectable differences in their tools.

Habitual habitats

It may seem like scientists working with unhabituated animals are making their lives more difficult than they need to. I know this firsthand: my own work with unhabituated wild monkeys has often left me with the barest of glimpses of the animals before they beat a hasty retreat to a safe distance into the forest or up an inaccessible mountain. But the fact is that habituation is the exception to the rule for many species. Bessa et al. make this point clearly in their study:

In West Africa, for example, only five chimpanzee communities are fully habituated to researchers…representing a total of approximately 200 individuals out of an estimated 52,811 chimpanzees in the region.

Let that sink in. Every close, long-term study of west African chimpanzees—the only communities known to use stone tools, by the way—comes from only a fraction of a percent of the animals that live in the area. Against this backdrop, studies like Bessa’s are vitally important for understanding not just how wild chimpanzees actually live their lives, but for correcting our own biases that may come from relying too heavily on the actions of a small minority of our close cousins.

This is cumbersome but critical work, with implications for protecting the animals themselves, as well the environments and cultures that sustain them. The Cantanhez chimpanzees, across multiple communities, know and practice honey-gathering in a complex social and physical environment that can never be replicated in a zoo, or a cage. As we increasingly threaten to tear down their natural worlds, we owe it to them to give them space not only to live, but to continue their unique ways of life.

Sources: Bessa, J. et al. (2021) First evidence of chimpanzee extractive tool use in Cantanhez, Guinea-Bissau: cross-community variation in honey dipping. Frontiers in Ecology and Evolution 9:625303. || O’Malley, R. et al. (2012) The Appearance and Spread of Ant Fishing among the Kasekela Chimpanzees of Gombe. A Possible Case of Intercommunity Cultural Transmission. Current Anthropology 53:650-663.

Main image credit: University of Oxford (Joana Bessa) || Second image credit: Vanne Goodall, National Geographic || Third image credit: Bessa et al. (2021) || Video credit: Bessa et al. (2021)