Chimpanzee stone-throwing websites might protect uncommon proof of primate tradition and communication.
In the savanna woodland of Boé National Park in Guinea-Bissau, a scarred tree can inform a wierd story. Around its base, rocks might lie in small piles, whereas its trunk bears the marks of repeated impacts.
The chimpanzees that made them might already be gone, however the scene can reveal proof of considered one of their rarest and most intriguing behaviors: accumulative stone throwing.
This habits has been recorded in wild western chimpanzees, most frequently grownup males. Video footage shows them hurling stones at particular trees, then returning to those same trees again and again to repeat the action.
The shows should not quiet. As they throw, the chimpanzees usually pant-hoot, a loud call that can carry over long distances. Some additionally strike the tree with their hands and toes in a habits often called buttress drumming.
Researchers have simply returned from a discipline web site in Guinea-Bissau, the place they gathered new knowledge to higher perceive the social and ecological setting of accumulative stone throwing. The aim is to find out what, if something, chimpanzees are speaking after they repeatedly throw rocks at the similar timber.
Because chimpanzees are our closest living relatives, this habits may offer clues about the deep evolutionary roots of communication and stone tool use. Understanding why they choose sure timber, why stones accumulate there, and the way the shows match into chimpanzee social life might assist researchers discover how extra complicated signaling and tool-related behaviors emerged over human evolution.
A cultural habits
Pant hooting and buttress drumming are each a part of the male chimpanzee show, suggesting that accumulative stone throwing may signify a modification of this widespread habits. It is likely a cultural behavior because of its restricted distribution, and since the availability of rocks and timber doesn’t assure the presence of an accumulative stone throwing web site.
Previous analysis means that accumulative stone throwing is probably going communicative or might also have a symbolic goal, with websites marking necessary places inside the chimpanzees’ territory.
However, we nonetheless don’t know what cumulative stone-throwing websites may imply to the chimpanzees themselves nor why they do it. While some primates use stone instruments to entry meals, as an example to crack open nuts, accumulative stone throwing is a uncommon instance of stone instrument use in a social context. It has been noticed in solely 4 chimpanzee teams in West Africa up to now.
Setting up camp
We traveled to the distant Boé chimpanzee territory in Guinea-Bissau and based mostly ourselves in Béli, a small village the place, in collaboration with native individuals, the Dutch non-governmental organization Chimbo maintains a compound. Visiting researchers and vacationers can keep right here and use a workspace with solar-generated electrical energy.
From Béli, we cycled and hiked 22 kilometers into the savanna-woodland to ascertain a bush camp with our two discipline assistants, Djei Baldé and Balu Séra, and a grasp’s pupil from the Great Ape Behavior Lab, Taylor Tippett.
The Boé chimpanzees performing the habits are unhabituated; they don’t seem to be used to people, that means that we can’t observe particular person chimpanzees on foot as a result of they’ll run away. Instead, we collected behavioral knowledge utilizing digital camera traps and recording units.
We arrange two video cameras at every accumulative stone throwing web site and positioned the recording units strategically to seize audio knowledge from the areas round these websites.
Our campsite bordered the Fefine, a big river that flows even in the dry season. In a panorama like the savanna-woodland the place water sources are scarce, rivers like the Fefine are necessary for wildlife and people alike. We captured a number of of our neighbors on cameras arrange close to the riverbank.
Chimpanzee nests
On a median day, we awoke round 6:30 a.m. and ate a small breakfast earlier than heading to a set of two to 5 websites. There, we changed the SD playing cards and batteries on the cameras, made certain the units had been working effectively and picked up any extra knowledge wanted, together with measurements of the tree and 3D scans of rocks thrown at the tree for later evaluation.
Along the means, we recorded observations of chimpanzee nests, feeding indicators, vocalizations, and sightings.
The video and audio knowledge we collected will enable us to analyze the social traits of accumulative stone throwing, together with the age and intercourse of the stone thrower and the viewers (different chimpanzees close by who may react to the throw). This info may also help us decide what chimpanzees are attempting to speak.
We discovered that the majority of the websites first recognized by the Pan African Program, and revisited by our group in 2017, had been nonetheless in use throughout our latest journey to the discipline, that means that chimpanzees can use these websites for over a decade.
The menace of bauxite mining
As many primate species face threats from human activities, cultural behaviors and the maintenance of rich cultural repertoires can help them adapt to environmental changes and provide support for conservation.
On top of its potential communicative importance and intrinsic value as a cultural behavior, accumulative stone throwing involves durable primate material culture, the loss of which would constitute the erasure of primate heritage.
Unfortunately, chimpanzee habitat in Guinea-Bissau is threatened by extractive industries, particularly industrial mining. While in the field, we encountered boreholes from bauxite mining exploration.
Bauxite mining represents a significant opportunity for economic growth and development in Guinea-Bissau. It can also cause habitat destruction and pollution with severe detrimental effects for chimpanzees, other wildlife, and the local people — as it already has in neighboring Guinea.
Environmental oversight and regulations are much needed, especially given the added challenges of unstable governance in Guinea-Bissau.
By studying and bringing attention to chimpanzee cultural behaviors like accumulative stone throwing, we hope to support chimpanzee conservation and the maintenance of biodiversity more broadly, as well as the preservation of primate cultural materials for future research and education.
Adapted from an article originally published in The Conversation.
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