The New Scientist magazine (February 2022) documents research on captive orangutans, which reveals that orangutans can learn how to use stone tools as hammers and knives. However, they can’t make the tools.
Researchers at the University of Tubingen in Germany have been studying the behaviour of captive orangutans.
Alba Motes Rodrigo and her colleagues studied two male orangutans at the Kristiansand Zoo and Amusement Park in Norway. The Bornean Orangutans (Pongo pygmaeus) are mammals in the Hominidae family of apes.
The orangutans were given a sealed box of fruit (it was sealed with rope), a concrete hammer, and a lump of blunt rock.
The researchers wanted to observe whether they would use the hammer to knock sharp flakes (shards) off the rock to use the shards as stone tools (knives) to cut the rope and open the box. In previous studies with orangutans, the researchers had seen them use rocks for hitting and using sharp objects for cutting, so they wanted to see if the orangutans could combine the skills to make a sharp tool and then use it for cutting.
The researchers found that the orangutans could not do this.
The orangutans being studied had never seen stone tools before, so they could not discover how to make a sharp object. They never learned how to make their own tools from raw stone, even after being shown how to do make them.
Alba Motes Rodrigo said, ‘We didn’t find the orangutans could combine these behaviours.’ The orangutans did hit things with the hammer and with the rock. ‘We found percussion, which is interesting because orangutans in the wild very rarely interact with stones at all.’ They rarely use stones in their natural habitat.
The researchers conducted a follow-up experiment.
The researchers gave the two male orangutans a sharp tool – a flint flake that was sharp, like an axe head.
After trying to open the boxes in different ways, one orangutan did use this sharp stone axe (that Alba Motes Rodrigo made) to cut the rope and open the box and obtain the reward (fruit). ‘They can spontaneously, without any training, recognise that a sharp stone can be used for cutting,’ said Motes Rodrigo.
In a third experiment, the researchers gave the orangutans sharp stones, then rewarded them with grapes if they handed them back to the researchers. This experiment aimed to encourage the orangutans to associate sharp stones with rewards.
The orangutan who had cut the rope in a previous experiment, now took the lump of blunt rock and smashed it until sharp shards broke off. Therefore, it seemed as if he was making a sharp tool. But the researchers said that he did not do anything with the sharp shards – he did not attempt to cut the rope. This suggests that he did not understand what he had just made.
In the last experiment, the researchers showed three other captive orangutans how to make sharp stone tools.
Even with repeated demonstrations, the orangutans never managed to make the tools. One orangutan started to hit the rock with the hammer, but only for a short time. The researchers think they need more than just demonstrations and observations. Alba Motes Rodrigo said, ‘Clearly, just observation wasn’t enough for this. There is something else that is missing here.’
The researchers don’t know yet whether the orangutans can’t understand the spatial relations involved in shaping and making tools or whether they can’t think far enough ahead to complete the sequence of activities – observe, imitate, make, and use.
Journal reference: PLoS One, DOI: 10.1371/journal.pone.0263343
Location of photographs: Paris Zoo, France
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM