original publications

1.
Normand, E., Ban, S.D., Boesch, C.
Sophisticated Euclidean maps in forest chimpanzees.
2.
Normand, E., Boesch, C.
Forest chimpanzees (Pan troglodytes verus) remember the location of numerous fruit trees.

Orientation

Mental map

The tropical rain forest in the Taï National Park in Côte d’Ivoire is a veritable jungle of brush, lianas and fallen trees. It is generally impossible to see further than 20 metres ahead. In this almost impenetrable environment, the chimpanzees must find their bearings, identify sources of food and drink, and mark out the boundaries of their territories. The search for food is particularly difficult as the trees, on which the chimpanzees feed, are widely dispersed. Moreover, their fruits ripen at different times of the year.

Emmanuelle Normand and her colleagues from the Max Planck Institute for Evolutionary Anthropology in Leipzig have discovered that the Taï chimpanzees have an excellent spatial memory and can pinpoint the locations of their favourite food trees without difficulty. The researchers created computer simulations of different possible search strategies and compared them with the animals’ actual migratory and feeding behaviour.  

The results of their analyses show that the chimpanzees visit certain rare tree species far more frequently than could be expected on a purely coincidental basis. Moreover, the animals are willing to cover long distances to reach their favourite heavily-laden fruit trees. The scientists see this as a clear indication that, thanks to their detailed spatial memory, the chimpanzees of the tropical rain forest can remember the locations of many food sources and use this knowledge to select the most attractive food sources.

But how exactly do the chimpanzees find their way in the dense undergrowth of the jungle? The Max Planck researchers studied the Taï chimpanzee’s sense of direction with a view to answering this question and have discovered that the animals know precisely where they are going. They move in a straight line to the next feeding place and are aware of the distance involved. Moreover, rather than always following the same route to reach the feeding places, they can approach them from different directions.

The research findings suggest that the chimpanzees use a mental map to move from one point to another. When the animals combine the distance they have travelled and the location of the food sources in their heads, the information is used to compile a kind of Euclidean map. Therefore, they do more than use known orientation points for their migrations like many other animal species. We humans also create Euclidean maps of our environment, but not until we reach the age of six or seven.

Harald Rösch

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How chimpanzees use tools

Image: Sonja Metzger

 
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