Wild chimpanzees plan their breakfast time, type, and location

Abstract

Not all tropical fruits are equally desired by rainforest foragers and some fruit trees get depleted more quickly and carry fruit for shorter periods than others. We investigated whether a ripe-fruit specialist, the chimpanzee (Pan troglodytes verus), arrived earlier at breakfast sites with very ephemeral and highly sought-after fruit, like figs, than sites with less ephemeral fruit that can be more predictably obtained throughout the entire day. We recorded when and where five adult female chimpanzees spent the night and acquired food for a total of 275 full days during three fruit-scarce periods in a West African tropical rainforest. We found that chimpanzees left their sleeping nests earlier (often before sunrise when the forest is still dark) when breakfasting on very ephemeral fruits, especially when they were farther away. Moreover, the females positioned their sleeping nests more in the direction of the next day's breakfast sites with ephemeral fruit compared with breakfast sites with other fruit. By analyzing departure times and nest positioning as a function of fruit type and location, while controlling for more parsimonious explanations, such as temperature, we found evidence that wild chimpanzees flexibly plan their breakfast time, type, and location after weighing multiple disparate pieces of information. Our study reveals a cognitive mechanism by which largebrained primates can buffer the effects of seasonal declines in food availability and increased interspecific competition to facilitate first access to nutritious food. We discuss the implications for theories on hominoid brain-size evolution.prospective cognition | flexible planning | ecological intelligence | interspecific competition | foraging strategies T hree decades ago, Katharine Milton hypothesized that the diversity of food and the manner in which it is distributed in space and time have been major selective forces in the development of advanced cerebral complexity (the ecological intelligence hypothesis) (1, 2). Positive associations between a variety of brain size measures and levels of frugivory (i.e., the dietary proportion of patchily distributed and ephemeral food) were found in primates (3, 4), bats, and rodents (5). However, the idea that body size evolves more rapidly than brain size, meaning the small relative brain size of folivores could be a nonequilibrial situation, kept scientists from interpreting these associations as clear support for Milton's hypothesis (6; but see also ref. 7). The ecological intelligence hypothesis was, however, retained as one of the four components of the technical intelligence hypothesis, developed to find evolutionary explanations of great apes' representational skills (6). It was renamed the "cognitive map hypothesis," which unintentionally focused attention solely on the complexity of the spatial mapping of food and largely ignored the potential difficulty of anticipating the time and duration that food is present.With recent comparative studies on brain size evolution, the role of the tempora...

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