Elsevier

Animal Behaviour

Volume 86, Issue 6, December 2013, Pages 1183-1205
Animal Behaviour

Chimpanzees use long-term spatial memory to monitor large fruit trees and remember feeding experiences across seasons

https://doi.org/10.1016/j.anbehav.2013.09.021Get rights and content

Highlights

  • We studied monitoring behaviour of fruit trees by chimpanzees in rainforest habitat.

  • Chimpanzees fed on and monitored significantly larger trees than other forest trees.

  • Most trees were monitored en route, but 13% were approached in a goal-directed way.

  • Such goal-directed monitoring was guided by a long-term spatial memory of tree size.

  • Information from previous feeding experiences was remembered across seasons.

We studied the nature of information that frugivorous foragers take into account to increase their chances of discovering bountiful fruit crops. We recorded the foraging behaviour of five adult female chimpanzees, Pan troglodytes verus, for continuous periods of 4–8 weeks, totalling 275 full days, throughout multiple fruiting seasons in the Taï National Park, Côte d'Ivoire. We found that chimpanzees fed on individual trees that were significantly larger than other available and reproductively mature trees of the same species, especially if their fruit emitted an obvious smell. Trees that were merely checked for edible fruit, but where monitoring could not have been triggered by olfactory or auditory cues because the tree did not carry fruit, were also significantly larger. Most trees were monitored along the way during travel, but 13% were approached in a goal-directed manner (assessed using a ‘change point test’). These approaches were unlikely to have been initiated by visual cues and occurred more often when females foraged solitarily and when trees were large as opposed to small. Our results suggest that goal-directed monitoring is guided by a long-term ‘what–where’ memory of the location of large potential food sources. These findings were confirmed in a quasiexperiment that tested which of 15 876 potential food trees with different crown sizes were approached in a goal-directed manner. Observations on one female who was followed intensively over 3 consecutive years indicated that monitoring probability was highest for trees with which she had become more familiar through frequent previous visits and that had carried more fruit, suggesting that she was able to remember this information across fruiting seasons. Long-term phenological data on individual trees indicated that the interval between successive fruiting seasons, and hence the ‘memory window’ of chimpanzees required for effective monitoring activities, could be up to 3 years.

Section snippets

Study Subjects and Data Collection

We followed five adult chimpanzee females during fruit-scarce periods, from 16 April 2009 to 30 August 2011, for successive continuous periods ranging from 4 to 8 weeks (total full days = 275). Their territory (South Group; 26.5 km2) was located in the largest remaining tract (5363 km2) of primary lowland rainforest in West Africa: Taï National Park, Côte d'Ivoire (Boesch et al., 2008, Kouakou et al., 2011, N'Goran et al., 2012). A target female was followed from the point of waking until

Did Chimpanzees Use Sensory Cues?

To investigate whether both feeding and closely inspected trees were larger than control trees, we tested the effect of the type of tree (as a within-subject factor) on trunk size. Overall, we found a significant difference between the trunk sizes of trees that were of the same species but different types (control trees, feeding trees and closely inspected trees that had an empty crown; RM-ANOVA: F2,38 = 64.31, P < 0.001; Fig. 3). The trunk sizes of trees in which chimpanzees fed were larger than

Discussion

By analysing the monitoring behaviour of five chimpanzee females, followed on foot for continuous periods of up to 8 weeks, we investigated chimpanzees' abilities to discriminate between small and large rainforest trees and the underlying cognition used to discover large fruit crops. We found that the focal animals preferentially fed on larger trees, compared to alternative conspecific trees of reproductive size encountered on control transects. The difference in trunk size between trees used

Acknowledgments

Financial support for this research was provided by the Max Planck Institute for Evolutionary Anthropology. In Côte d'Ivoire, we thank the Ministère de la Recherches Scientifiques, the Ministère de l'Environnement et des Eaux et Forêts, the Office Ivoirien des Parcs et Réserves, the directorship of the Taï National Park, the Centre Suisse de Recherche Scientifique, L. Wittiger, D. Dowd, A. Diarrassouba, I. Kone and S. Kone for logistic support and permission to conduct our studies. We are

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