Chimpanzees use botanical skills to discover fruit

To investigate if chimpanzees know that if a tree is carrying fruit, then other trees of the same species are likely to carry fruit as well, the researchers conducted observations of their inspections, i.e. the visual checking of fruit availability in tree crowns. They focused their analyses on recordings in which they saw chimpanzees inspect empty trees, when they made "mistakes."

By analysing these "mistakes," the researchers were able to exclude that sensory cues of fruit had triggered the inspection and were the first to learn that chimpanzees had expectations of finding fruit days before feeding on it. They, in addition, significantly increased their expectations of finding fruit after tasting the first fruit in season. "They did not simply develop a 'taste' for specific fruit on which they had fed frequently," says Karline Janmaat. "Instead, inspection probability was predicted by a particular botanical feature -- the level of synchrony in fruit production of the species of encountered trees."

The researchers conclude that chimpanzees know that trees of certain species produce fruit simultaneously and use this information during their daily search for fruit. They base their expectations of finding fruit on a combination of botanical knowledge founded on the success rates of fruit discovery and an ability to categorize fruits into distinct species. "Our results provide new insights into the variety of food-finding strategies employed by our close relatives, the chimpanzees, and may well elucidate the evolutionary origins of categorization abilities and abstract thinking in humans," says Christophe Boesch, director of the Max Planck Institute for Evolutionary Anthropology's Department of Primatology.