Abstract:

Human population increases and an expanding agricultural frontier are driving tropical
deforestation. As a result some of the indigenous tree species which serve as primate foods are
likely to become rare or even extinct from the wild. A better understanding of the nutritional
composition of different primate foods and how primate species cope with the changes in diet
quality due to fluctuating food resources is critical for conservation efforts. Previous studies
indicated that Kibale chimpanzees prefer high-quality drupe fruits and the timing of reproductive
events i.e estrous, conceptions and births is often associated with availability of drupes. It has
thus been commonly assumed that consumption of drupe fruits leads to increased energy intake
which favours reproduction in female chimpanzees. Against this background I focused on the
female chimpanzees (Pan troglodytes schweinfurthii) of Kanyawara community in Kibale
National Park, and: 1) examined whether dietary variation relates to macronutrient and energy
intake variation; 2) applied the principles of nutritional geometry to examine the nutritional
strategy of female chimpanzees; and 3) examined whether macronutrient intake variation relates
to the timing of reproductive events in female chimpanzees. Fruit seasonality resulted into
variations in macronutrient intake while energy intake was relatively stable. Female chimpanzees
switched their diet and adjusted their behavior in order to maximize intake of high-quality
nutrients, minimize foraging costs and acquire a nutritionally balanced diet. Similar to
frugivorous spider monkeys (Ateles sp.) and humans, female chimpanzees tightly regulated
protein intake while maximizing carbohydrate intake. The results also indicated that there was no
predictable seasonality in the timing of reproductive events or in macronutrient or energy intake.
While the patterns of timing of reproductive events were not consistent with the patterns in the
intake of high-quality macronutrients, there was a positive relationship between energy intake
and estrous and births. Additionally the findings suggest that minimum temperature has an effect
on the estrous and conceptions. Since increase in minimum temperature negatively affects
fruiting in tropical forests, there is a likelihood that female chimpanzees are using minimum
temperature as a cue for predicting fruit availability. The increased consumption of
carbohydrates and reduction of foraging costs during drupe months might allow female
chimpanzees to reach a positive energy balance thereby resuming cycling when drupes are
abundant. This study, supports the increasing recognition of nutrient balancing as a foraging
strategy used by female chimpanzees and the relevancy of using feeding rates to estimate intake
in wild primates. Furthermore, the study provides insights on the relevancy of the different food
types in chimpanzee habitats and this information can be used to better manage chimpanzee
ecosystems and captive chimpanzee populations.