Abstract
In the shade of the dense foliage of the central African rainforest, a western gorilla (Gorilla gorilla) spends almost a third of its daytime feeding. Each day, it needs more than 5 000 kcal and travels several kilometres to find enough food. On the efficiency of its search may depend its fitness. If natural selection could have influenced the capacities that facilitate digestion and perception of resources, or locomotion, it could also have influenced the ability of this great ape to process, memorise and reuse long-term knowledge that allows it to when, where, and what resources can be found. This dissertation aims to better understand the involvement of cognition in foraging in western gorillas, and more broadly in primates. We first fill a theoretical gap and illustrate through agent-based simulations how temporal memory can improve foraging efficiency in a variable but predictable environment, such as the seasonal tropical forest where western gorillas live. We rely afterwards on long-term monitoring of five groups of western gorillas in central Africa, habituated to human presence, as well as on a botanical and phenological inventory of their food resources, to show the existence of a spatio-temporal memory in this great ape species. To do so, we focus on two behaviours: the restriction of movement within a home range, and feeding choices. We then highlight some of the spatial cognitive mechanisms underlying movement by focusing on gorillas' use of widely dispersed but resource-specific swamps and of a network of forest elephant trails. These studies highlight the existence of accurate spatial memory at large scale, with topological encoding of information. We then show how spatio-temporal knowledge is used insensitively to resource spatio-temporal variations by analysing movement patterns and recursions to feeding sites. Finally, we extend our horizon through several multi-species studies that focus on (a) an experimental approach, in order to link cognitive foraging strategies and degree of frugivory in primates; (b) an opinion paper proposing a standardised methodology to compare cognition related to movement in wild primates; (c) a phylogenetic approach, in order to understand the influence of sympatry between frugivorous primates on the evolutionary history of their cognition and their diversification. This dissertation thus contributes to unveil the proximal and ultimate mechanisms shaping foraging strategies and cognition in primates.