Taï chimpanzees change their travel direction for rare feeding trees providing fatty fruits

Abstract

The production of edible rainforest fruits is characterized by fluctuating and seasonal patterns that require frugivores to flexibly adjust their ranging behaviour. We investigated whether significant changes in a forager's travel direction can inform us about the importance of the nutritional and energetic aspects of different food sources for a wild animal's diet. We recorded the ranging patterns of five adult female chimpanzees, Pan troglodytes verus, for a total of 275 full days in the Tai National Park in Cote d’Ivoire and designed two models that predicted their directional changes at, and on the way to, fruit-bearing feeding trees. In both models, directional change was significantly influenced by the density of the feeding tree species and the crude fat content of that species' fruit. Female chimpanzees were more likely to change their travel direction for rarer trees, at which they fed on fruits that contained higher amounts of fat. In addition, directional changes tended to be positively influenced by the content of nonstructural (‘easy energy’) and structural carbohydrates (NDF) in that species' fruit. We did not detect any effect of sensory cues or social factors on the directional changes, in either model. The amount of fruit available and the time since the start of the fruiting season positively influenced directional change in the second model, which suggests that chimpanzees were updating their knowledge of the fruit availability in individual trees over time. Our results indicate that the nutrient content of fruit and its abundance exerted a significant impact on the shape of chimpanzee female travel paths, which opens up a new avenue for investigation of food preferences in wild animals through analyses of their ranging patterns.