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Gorillas and Tools - Part I

Marina Vančatová  18.08.2008
Moja uses crates for different purposes - Autor:Khalil Baalbaki
Moja uses crates for different purposes
Autor:   Khalil Baalbaki  

Our observations at the Prague Zoo showed that gorillas in captivity use tools quite often, depending on the situation. Over the past twelve months, I have observed more than 1500 instances of tool use. 

The cases can be categorised as follows:

1. Spontaneous use of crates as stools
In December 2005, we observed spontaneous use of crates for transporting vegetables that the gorillas were free to use indoors. Upon her arrival in the Prague Zoo from Dvur Kralove, Kamba was placed in separated quarters of the pavilion. All members of the original troop were able to watch Kamba through a glass window, which all the adults did. Kijivu and Shinda spent a lot of time watching Kamba, standing at the window on their hind legs (bipedal posture). However, the height of the window is suited for humans. Female gorillas are shorter, so they had to stand really upright to see Kamba at all. After some time, both females fetched the crates and stood on them (quadrupedal posture) to have a better view of Kamba. They also put the crates on the short edge to to reach higher. They sat on the crates and watched Kamba through the window. Shinda then brought another crate and put it on the other to make a pyramid. Then she climbed up the pyramid and continued watching Kamba. Both females, Kijivu and Shinda, commonly use crates as stools or steps to reach higher. For instance, Shinda often steps on the crate and then tries to reach higher places in the pavilion by climbing up the walls using various projections and recesses. They use wicker baskets and balls for the same purpose.

Where shall I put it? - Autor:Khalil Baalbaki
Where shall I put it?
Autor:   Khalil Baalbaki  

2. Spontaneous use of crates as stools
We subsequently conducted an experiment. We hang carrots in the enclosure so high that the gorillas could not reach them. Shinda and Kijivu used crates as stools to reach the carrots: they fetched them from another part of the enclosure, stood under the carrots, stepped up on them and picked the carrots. Similar behaviour was observed in chimpanzees (Kohler, 1927, Firsov, 1977). In our experiment, we were only interested whether gorillas can use tools in the given situation and whether they would use them in the same way as chimpanzees.

3. Spontaneous use of crates as a table or tray
Adult male gorillas Richard used a crate as a table or a tray on which he carried a birthday cake. He walk on the hind legs (bipedal walk). He held the crate with the cake in his hands. He had to cross a large trunk and continued walking on two.

Kamba in action - Autor:Khalil Baalbaki
Kamba in action
Autor:   Khalil Baalbaki  

4. Spontaneous use of crates or other objects as weapons
Another spontaneous use of crates was observed in violent conflicts, when the crates served as weapons. This behaviour manifested strongly in the first days after Kamba joined the troop, when fights were relatively frequent. The gorillas would throw the crates against the opponent. We observed similar behaviour at the Prague Zoo in 1988. Male Assumbo used to remove bits of bark from tree stumps in the outer enclosure and throw them at the visitors.
In 1999 at the Apeldoorn Zoo in the Netherlands, we saw a juvenile male use wooden sticks as a weapon against his peers.

5. Creation and use of a tool in experimental situation
In order to bring variety into feeding patterns in the troop, keepers place food in different parts of the enclosure, into various openings, etc. Adult male Richard obtains a chunk of wood with holes from the keepers. The holes are filled with raisins. Richard first makes a thin stick by biting off a piece of a branch and then uses the stick to dig out the raisins.

Branches are versatile tools - Autor:Khalil Baalbaki
Branches are versatile tools
Autor:   Khalil Baalbaki  

6. Spontaneous use of a branch to reach food
A keeper left a bowl with fruit on the floor outside the gorillas' reach and left. Richard could see the bowl through the bars. He picked a branch in the enclosure and tried to reach for the bowl with it to get it closer to the bars. Shinda uses a branch to reach for plants growing below the ceiling. Moja has learned similar skills by imitating Shinda.

7. Spontaneous use of parts of a tree trunk as a ladder
We observed spontaneous use of tools by an adult female in summer 1999 at the Apeldoorn Zoo in the Netherlands. The situation was as follows: there are large live trees in the outer enclosure. They are protected by concrete barriers up to approximately 3 metres of height to prevent animals from climbing the trees. One of the adult females brought a large wooden log to one of the trees, leaned it against the concrete barrier and climbed up on it like on a ladder to reach the upper edge of the barrier and on to the tree. She then sat in the crown of the tree munching leaves and twigs.

8. Spontaneous use of crates as drums
Female gorillas at the Prague Zoo often drum on the crates. This type of drumming is different from agonistic chest-beating and is part of the gorillas' game-like behaviour.

9. Spontaneous use of crates as drums in agonistic behaviour
In this case, the drumming was not a game but a manifestation of agonistic behaviour. Gorillas held the crates against their chests and beat it the same way as males beat their chests in aggression. The drumming was followed by an attack against another member of the troop at which the crates were hurled. We have not observed this type of behaviour or hints of it anywhere else but the Prague Zoo.

Wood wool is an excellent material - Autor:Khalil Baalbaki
Wood wool is an excellent material
Autor:   Khalil Baalbaki  

10. Spontaneous use of bedding as a cushion
Adult females at the Prague Zoo often collect the bedding (wood wool), pile it up and use as a pillow when they sit on hard surfaces (rugged washable floor).

11. Spontaneous use of various objects to build a nest
Gorillas at the Prague Zoo use many different objects in the enclosure to build nests on the ground, such as bedding (wood wool), bits of fabric, paper, dismantled cardboard boxes, branches, etc. The gorillas put those objects around themselves when sitting on the floor. They often lie down in such nests (Zdansky, Vancatova, 2002).

12. Spontaneous use of wood wool as primitive shoes
In winter, we observed female Kijivu to use chunks of wood wool as "slippers" when walking on the snow. She held them in place with her toes. We observed similar behaviour a year later when the floor in the enclosure was wet after cleaning. Kijivu used chunks of the wood wool as primitive footwear to cross a wet section of the floor.

This article by primatologist Marina Vancatova about the use of tools by gorillas is to be continued in the coming days.


 

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