Usage of tools by gorillas was long outside the focus of scientific research. It was commonly thought that gorillas do not use tools very much, unlike chimpanzees and orang-utans who use tools commonly in the wild as well as in captivity. Whenever usage of tools was observed in captive gorillas, it was attributed to imitation of human behaviour.
Three years ago, research showed use of tools by wild gorillas. The Revealed project has enabled us to monitor behaviour of a gorilla troop in captivity on a daily basis. Over the past year, we have observed more than 1500 instances of tool use by gorillas at the Prague Zoo. This cannot be interpreted as acquired, human-affected behaviour. Many a time we have witnessed spontaneous use of tools in the absence of humans. That is why we analysed this type of behaviour more closely.
First of all, we had to classify objects that can serve as tools. The classification is as follows:
1 - paper
2 - stick - stick, branch, piece of wood and similar objects
3 - box - box, crate, basket and similar objects
4 - substrate - bedding and other filling materials
5 - fabric - cloth, strips, bags, etc.
6 - rope - strings, ropes, nets
7 - food - any type of food
8 - animal - animals that apes encounter and use them as a tool (live ladder, steps, etc. - Tatu climbs on adults or Moja to reach higher)
Use of tools in the context of the activity
Adult gorillas, with one exception, used plastic crates and baskets for various purposes. There is a marked difference between males and females as to use of tools. Females tend to use tools more often for a wider range of goals. Males use tools primarily as weapons, whereas females are very creative and have been observed to use the plastic crates as weapons, nests, steps, and drums. Many activities are quite unusual, e.g. drumming, which substitutes chest-beating. The crates are used as steps in many different situations.
Use of hands for manipulation with tools
Adult gorillas, like orang-utans, often use both hands to manipulate with objects. When they use one hand only, they tend to be right-handed.
Use of hands in the context of the activity
Adult gorillas hold weapons either in their right hand or in both. Females are most often double-handed, whether in manipulation with the tool or its use, with one exception: they hold a weapon almost exclusively in their right hand.
Working a tool into required shape
Gorillas work their tools only rarely. We need to realise, though, that plastic crates can hardly be adapted in some sophisticated way. The gorillas are aware that they do not need to improve or disintegrate the crates in any way. They found that simple manipulation with the boxes is much more effective and use them as building blocks, which is an advanced use of tools in a way. Shinda does not adapt the branch she uses to reach plants very much (she does not break off little twigs and leaves). Nevertheless, we should note that for gorillas, unlike for other apes, a branch is not just a tool but also common fodder. Sometimes, we can observe adaptation of tools - for instance, Richard is well known for his ability to make a tiny pick from a branch.
Behaviour and context of tool usage
Males use plastic crates or sticks as weapons in agonistic behaviour. Females use plastic crates in a wide range of behaviours, most often in play, feeding, and nesting, as well as in agonistic and social behaviour. A plastic crate is a versatile tool. It remains to be seen how tool use develops further in the Prague Zoo gorillas, because a plastic crate is not a natural tool for them. Tool use is clearly innovative from the point of view of both the context and type of behaviour.
Plastic crates and baskets have become versatile tools for the Prague Zoo gorillas, similar to a stick for chimpanzees. It might be a looming tradition in the case of the gorillas but a tradition that has no analogy in the wild. On the other hand, use of the plastic crates has become part of rituals, e.g. in agonistic behaviour, when they are used to discharge aggression or to amplify drumming.
Generally, we can say that gorillas are quite advanced in their use of tools in captivity. The variety of this type of behaviour depends largely on the objects available to them. Due to security reasons, there are no stones in the enclosure. That does not mean that gorillas would not be able to use them as tools. There is a report from a gorilla rescue centre in Africa where gorillas had access to stones. I hope the gorillas at the Prague Zoo will continue to surprise us with their inventiveness and creativity.
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