Food preferences of wild mountain gorillas.

Determining the nutritional and phenolic basis of food preference is important for understanding the nutritional requirements of animals. Preference is a measure of which foods would be consumed by an animal if there was no variation in availability among food items. From September 2004 to August 2005, we measured the food preferences of four wild mountain gorilla groups that consume foliage and fruit in Bwindi Impenetrable National Park, Uganda, to determine what nutrients and phenols are preferred and/or avoided. To do so, we asked the following questions: (1) Which plant species do the gorillas prefer? (2) Considering the different plant parts consumed of these preferred species, what nutrients and/or phenols characterize them? (3) Do the nutritional and phenolic characteristics of preferred foods differ among gorilla groups? We found that although some species were preferred and others were not, of those species found in common among the different group home ranges, the same ones were generally preferred by all groups. Second, all groups preferred leaves with relatively high protein content and relatively low fiber content. Third, three out of four groups preferred leaves with relatively high sugar amounts. Fourth, all groups preferred pith with relatively high sugar content. Finally, of the two groups tested, we found that the preferred fruits of one group had relatively high condensed tannin and fiber/sugar contents, whereas the other group's preferred fruits were not characterized by any particular nutrient/phenol. Overall, there were no differences among gorilla groups in nutritional and phenolic preferences. Our results indicate that protein and sugar are important in the diets of gorillas, and that the gorillas fulfil these nutritional requirements through a combination of different plant parts, shedding new light on how gorillas balance their diets in a variable environment.