Wild bonobo (Pan paniscus) leaf umbrellas

If Neanderthals were still alive today, would we see ourselves differently? Has being the only surviving human species shaped our worldview? It’s a question that’s been around as long as we’ve known about our extinct hominin cousins: in 1921 H.G. Wells wrote ‘The Grisly Folk’ about them, as did William Golding in 1955’s The Inheritors (although if you want a more up to date Neanderthal picture, I suggest Rebecca Wragg Sykes’ superb Kindred from 2020).

For our closest living relatives, however, this question isn’t one of fiction or archaeology. Humans are equally related to two great ape species in Africa, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). The former have drawn more attention over the years—they’re the ones Jane Goodall befriended, they lead on the Planet of the Apes, and they are the non-human masters of tool-use. It wasn’t until 1933 that the bonobo was even recognised as a separate species, instead of a smaller or ‘pygmy’ version of a chimpanzee. It’s fair to say bonobos have often lived in the shadow of their famous primate sisters.

Here’s one now, posing for the Leakey Foundation cameras:

The two apes diverged around 2 million years ago, several million years after our own hominin line had split off. The bonobos were isolated to the south of the newly forming Congo River, with that barrier preventing most (but not all) subsequent genetic contact with chimpanzees. Unlike us and Neanderthals, though, both great ape species survived into the 21st century, giving us a chance to directly compare their behaviour. So let’s do that. Today we’re looking at a particular type of tool use rarely seen for wild chimpanzees, but favoured by the bonobo: leaf umbrellas.

Tooling in the rain

The basis for this post is a 2022 study led by Liran Samuni of Harvard University, with colleagues from the Kokolopori Bonobo Research Project in the Democratic Republic of the Congo (DRC). The Kokolopori Bonobo Reserve was established by the Congolese government in 2009, and three wild bonobo groups in the reserve have been habituated to human presence. Habituation takes time, slowly and carefully getting the animals used to having humans observing and following them at a distance. Once habituated, the bonobos pay little attention to the research team, acting in natural ways, and in return this familiarity allows the researchers to identify individual animals and track their social relationships.

This map from the Project’s site shows how the three habituated groups, and another bonobo group (Bekako) have both separate and overlapping parts to their territories:

The Kokolopori scientists started looking at tool use specifically in 2016, and the leaf umbrella observations were made in late 2019 and early 2020. Wild bonobo tool use is much less studied in general than that of chimpanzees, and at the time of this work early attempts were being made at compiling a list of behaviour across research sites.

For example, a 2015 report led by Takeshi Furuichi of Kyoto University found 13 different types of tool use at the Wamba and Lamako bonobo sites (also both in the DRC). These all involved using plant parts or moss, such as swatting insects with a leafy twig, cleaning oneself with leaves, and using branches and leaves for a variety of social signals. Bonobo leaf umbrellas were known from the Wamba site, but not seen at Lamako. Interestingly, only one type of foraging tool—a moss sponge for drinking water—has ever been found at a bonobo site, in contrast to the wide variety of pounding, probing and sponging tools known to be used for feeding by wild chimpanzees. Overall, the number of tools used by a given bonobo community seems to fall within, but towards the lower end of, the range seen for chimpanzee groups.

At this point it’s probably best if we take a look at a short video of a bonobo using a leaf umbrella, so you can picture exactly what we’re talking about. In the video below, taken by primate gesture expert Kirsty Graham, an adult male bonobo named Turkey starts with a leafy branch that he’s detached. The branch has side twigs that he needs to gather together, creating a sufficiently dense mat of leaves to protect him from the rain dripping through the forest canopy. It takes him a few attempts to be satisfied:

Not all leaf umbrellas need to have this size or complexity, for example they might just involve a single branch. One thing to note is that Turkey has created an umbrella in precisely the opposite way to how our human ones normally function, by bundling the leaves together rather than fanning them out. Without any fabric between the spreading twigs, like we have covering the thin ribs of our umbrellas, that’s the best way to form a protective mat. In some cases the bonobo holds onto the finished product overhead, while in others they might let go of it and let it rest on their head and back, in which case it becomes more of a rain hat than an umbrella.

As usual with wild animals (even habituated ones), the Kokolopori researchers faced obstacles in recording this behaviour. As their report notes:

The observation conditions of leaf‐umbrella usage were particularly challenging due to heavy rainfalls, a decrease in light intensity, and because the bonobos typically climbed high in the canopy during these events.

In other words, among the worst possible conditions for trying to precisely track wild animal behaviour. Nevertheless, Samuni and her team persevered and were able to spot 44 umbrella uses during 21 rain storms. Female bonobos made and used umbrellas more than twice as often as males, and all three habituated communities at Kokolopori had at least some examples.

There was individual variation too. The equivalent of those people who are always ready for wet weather were an adult male and female bonobo from the Ekalakala group named Noir and Violette. Between them they accounted for 12 of the 44 umbrellas that the soaked scientists observed. Another three times a bonobo just pulled over a nearby branch to act as a shelter, without breaking it off from the tree. It’s debatable whether we should also consider this tool use (what do you think?), but as we’ve seen elsewhere in this blog, the nice divisions we like to place between tool use and other kinds of natural object use aren’t usually foremost in the minds of the animals we’re watching.

From the paper, here’s alpha male Noir, hunched over with his umbrella/hat placed over his neck and upper back:

Oh, and you know that thing where you shake the gathered water off your umbrella and then go on using it? Bonobos do that too. Sometimes they even gave the leaves a bit of a squeeze to dry them off. One time Simone, another adult female, kept her umbrella while moving from one tree to another so she could re-use it, but most of the time the tools were left behind and forgotten as the bonobos moved off after the storm. Again, I can relate.

Sister act

What can we learn by comparing bonobo umbrella use with tools made by their sister species, the chimpanzees? For one, it seems notable that even chimpanzees that live in rainy environments (not all do) haven’t developed this kind of technology. Only at one chimpanzee site, Goualougo in central Africa, have these apes been seen making and using what the researchers there—Crickette Sanz and Dave Morgan—termed a ‘rain cover’. This tool involved chimpanzees detaching leafy twigs, just like the bonobos do, but they were placed on the body rather than held overhead, similar to the rain hat idea. Rain isn’t just an annoyance, it can seep away body heat, so it is the kind of behaviour we might expect to see more of among the inventive chimpanzees.

In their report, Samuni and her colleagues consider a range of options for this discrepancy. One idea at this point is that there could be a difference between the apes in the necessity or process for managing heat and comfort. It may also be that the forest canopy provides different levels of cover for the two ape species, or chimpanzees use strategies that make sheltering under existing branches an easier option than tool manufacture. There may even be a cultural element involved, in which some communities (e.g., Wamba and Kokolopori bonobos) have invented and embedded umbrella use as being ‘the done thing’ in their social groups, while in others (e.g., Lomako bonobos, most chimpanzees) the idea either hasn’t caught on or hasn’t been popular during the time that scientists have been watching out for it.

And I should emphasise that watching wild bonobos is still quite a niche activity compared to the coverage given to chimpanzees over the past six decades. It involves not just unhabituated animals, but a lot of often inaccessible territory. For context, here’s a photo of the field camp for the Kokolopori Bonobo Research Project (via their website), which should give you an idea of both how much territory there is to cover, as well as how dedicated and resourceful people like Liran Samuni and her local experts are to get any results at all. I think it’s fair to say we’ll be learning a lot more about our overlooked bonobo cousins and their tools as work progresses:

Sources: Coolidge, H. (1933) Pan paniscus. Pigmy chimpanzee from south of the Congo river. American Journal of Physical Anthropology 18:1-59. || Haslam, M. (2014) On the tool use behavior of the bonobo-chimpanzee last common ancestor, and the origins of hominine stone tool use. American Journal of Primatology 76:910-918. || Samuni, L. et al. (2022) Tool use behavior in three wild bonobo communities at Kokolopori. American Journal of Primatology 84:e23342. || Furuichi, T. (2015) Why do wild bonobos not use tools like chimpanzees do? Behaviour 152:425–460. || Kokolopori Bonobo Research Project; https://projects.iq.harvard.edu/kokolopori/KBRP. || Sanz, C. & D. Morgan (2007) Chimpanzee tool technology in the Goualougo Triangle, Republic of Congo. Journal of Human Evolution 52: 420-433.

Main image credit: Ley Uwera for NPR; https://www.npr.org/sections/goatsandsoda/2021/03/20/978868116/some-generous-apes-may-help-explain-the-evolution-of-human-kindness?t=1643707445736 || Second image credit: Leakey Foundation; https://leakeyfoundation.org/wp-content/uploads/2015/07/PRF-homepage-slider-1500x670.jpg. || Third image credit: Kokolopori Bonobo Research Project; https://projects.iq.harvard.edu/kokolopori/KBRP. || Video credit: Kirsty Graham; https://www.youtube.com/watch?v=ZabtQxFWNew || Fourth image credit: Samuni et al. (2022) || Fifth image credit: Kokolopori Bonobo Research Project; https://projects.iq.harvard.edu/kokolopori/KBRP.