The chimpanzees in the Taï Forest in Côte d’Ivoire use a hammer and anvil to crack five different types of nuts. Stones or wooden sticks act as hammers and the anvils are provided by blocks of stone or hard tree roots. Although suitable materials are rarely available in the rain forest, the chimpanzees are very fussy when choosing them. They are always on the lookout for the best possible tools, even if they have to be transported over long distances.
The material and size of the hammers used vary not only according to the hardness of the nuts, but also between neighbouring chimpanzee groups. Therefore, selection is a culturally learned behaviour which is passed on from one generation to the next within a group. The chimpanzees always get together in the same places to crack nuts. A Research Group led by Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology in Leipzig came across a nut-cracking “workshop” of this kind, which is probably over 100 years old. They excavated over 40 kilograms of nut shells and 4 kilograms of stone at this “Panda 100” site. The stones exhibited the typical flaking produced by the shattering of nuts.
At another location Christophe Boesch and his colleagues discovered a much older nut-cracking station: the tools from the Noulo site are 4,300 years old and, expressed on a human timescale, originate from the Late Stone Age. The scientists were even able to identify the type of nuts used at the site based on different starch granules on the rocks. The findings prove that West African chimpanzees have been cracking nuts using stone tools for thousands of years.
The chimpanzees learn to use the tools with great skill from a young age. It takes several years for them to master the technique completely. Animals as young as three make their first attempts at cracking nuts using their mothers’ hammers. The mothers not only share nuts with their children over the years, they also show them how to crack the nuts and help them if they have difficulty mastering the technique.
As the scientists discovered, when it comes to nut cracking, the adult females are more successful than the males. This applies to both the number of blows they require to open the nuts and the volumes they process. The females also regularly use the most difficult nut-cracking techniques. For example, they are skilled at cracking extremely hard Panda nuts and they can climb up Coula nut trees with their tools so that they can crack the nuts at lofty heights immediately after harvesting them.
Christophe Boesch and his colleagues observed a particularly complex form of tool use in Loango National Park in Gabon. The chimpanzees living there use three to five different tools in succession to extract honey. For bee nests located in trees that are not directly accessible, they use thick blunt sticks to break open the entrance to the nest, and thinner sticks to access the chambers inside the bee nest. They then dip a small stick with a frayed end in the honey or scoop the honey out using a broad piece of tree bark similar to using a spoon. They even use multifunctional tools with one smooth and one frayed end. The chimpanzees can also access the nests of bees that live underground. To do this, they poke the area near an entrance tunnel at ground level with a long straight stick until they reach the nested chambers. Complex intellectual skills are needed to exploit these concealed sources of honey. This kind of sequential tool use is comparable to some techniques used by humans in the Early and Middle Stone Age.
The chimpanzees also use tools to catch the five species of driver ants (Dorylus spp.) they feed on: they break off a small branch, trim it to the correct length and plunge it directly into the anthill. Some of the soldier ants bite the stick and are then transported directly into the mouths of the Taï chimpanzees. The animals use different techniques depending on the aggressivity of the ant species involved: when fishing for fast and combative ants, the chimpanzees in the Taï-Forest use longer sticks to protect themselves against painful ant bites. In the case of the less aggressive species, they remove the larvae and eggs directly from the anthill by hand. Cultural differences exist between different populations in relation to the ways in which chimpanzees fish for ants. Chimpanzees in Côte d’Ivoire and their counterparts in neighbouring Guinea catch and consume the same ant species in different ways. Their techniques vary, for example, in relation to the length of the sticks used.
Schimpansen machen auch die Nester unterirdisch lebender Bienen ausfindig. Dazu stochern sie neben einer an der Oberfläche mündenden Eingangsröhre mit einem langen, geraden Stock im Boden, bis sie auf die verschachtelten Kammern stoßen. Um die nicht sichtbare Honigquelle zu nutzen, sind komplexe geistige Fähigkeiten notwendig. Diese Form von sequentiellem Werkzeuggebrauch ist mit einigen Techniken der Menschen in der frühen und mittleren Steinzeit vergleichbar.
How chimpanzees hunt together