PHENOLOGY OF FRUITS CONSUMED BY A SYMPATRIC POPULATION OF GORILLAS AND CHIMPANZEES IN KAHUZIBIEGA NATIONAL PARK, DEMOCRATIC REPUBLIC OF CONGO

Abstract

Monthly fl uctuations in the abundance of fruits eaten by a sympatric population of gorillas (Gorilla beringei gaueri) and chimpanzees (Pan troglodytes schweinfurthii) were estimated by a transect system and a fruit trail system in the montane forest of Kahuzi-Biega National Park, Democratic Republic of Congo. Fruit species eaten by gorillas and chimpanzees and their preferences were defi ned mainly by fecal analysis. Data were collected for 80 months from 1994 to 2002, with a period of forced inactivity due to the civil war in 1997. A belt transect 5, 000 m long and 20 m wide was set up in the study area to pass through most of the vegetation types in which gorillas and chimpanzees range, and 2, 033 trees, including shrubs and strangling fi gs, above 10 cm in diameter at breast height (DBH) of 49 species from 29 families were identifi ed. Of these, fruits of 21 (6) species and 25 (12) species were eaten (preferred) by gorillas and chimpanzees, respectively. The fruit species preferred by gorillas were also preferred by chimpanzees. Monthly fruit index calculated from total basal area per ha and the proportion of the number of trees in fruit for each species shows a larger fl uctuation in the abundance of fruits eaten by chimpanzees than that by gorillas. Unlike the phenology of fruits in the lowland tropical forests, monthly fl uctuation in ripe fruit abundance negatively correlated with rainfall in some years. This tendency was more distinct for fruits preferred by gorillas in the primary forest. Fruit species preferred only by chimpanzees showed a distinct intra-specifi c synchrony in fruiting, while fruit species preferred by gorillas and chimpanzees did not. These differences in fruiting patterns may infl uence the foraging patterns of gorillas and chimpanzees. Gorillas tended to travel widely in a cohesive group and to increase their consumption of fruits in the primary forest during the dry season. By contrast, chimpanzees tended to continuously visit particular fruiting trees individually in a small home range throughout the entire year. Some tree species that have large basal areas and that bear fruits for a long period may be able to support the survival and sympatry of gorillas and chimpanzees.