Sophisticated Euclidean maps in forest chimpanzees

Abstract

We examined the spatial orientation abilities of wild chimpanzees, Pan troglodytes verus, in Taï National Park, Côte d'Ivoire. Predictions resulting from the hypothesized use of topological maps and Euclidean maps in a tropical forest were tested using quantified measurements of travel direction, distance travelled and routes based on landmarks. The results strongly suggest that the chimpanzees knew precisely where they were going, travelled in a straight line to reach food resources, and were aware of the distance they were going to walk. They also returned to a food resource from many different directions rather than repeatedly using the same paths. Furthermore, the initial direction taken to reach a food source corresponded exactly to the general direction needed to reach that resource suggesting that they did not navigate by landmarks to reach the goal. To control for the possibility that chimpanzees may remember numerous landmarks allowing them to navigate as precisely as if with a Euclidean map but in reality only using a topological one, we compared movement patterns in the core and peripheral areas of the territory, as they used the latter 75% less frequently. We found no variation in the linearity of movement, but a reduction in the distance travelled at the periphery, which corresponds to the possibility that the chimpanzees used a Euclidean map to navigate between resources. All these results provide additional support for the use of a Euclidian map in chimpanzees and we discuss how particular ecological conditions could favour the development of such sophisticated spatial orientation abilities in primates.