Foraging Ecology of Three Sympatric Turacos in a Montane Forest in Rwanda

Abstract

-We studied the foraging ecology of three sympatric turacos (Great Blue Turaco [Corythaeola cristata], Ruwenzori Turaco [Musophaga johnstoni], and Black-billed Turaco [Tauraco schuettii]) in a tropical montane forest in Rwanda between November 1991 and December 1992. All three species fed primarily on fruit. Whereas Black-billed Turacos were strictly frugivorous, Great Blue and Ruwenzori turacos were partially folivorous; leaves constituted 25% and 6.3% of their overall diets, respectively. The overall dietary diversity was highest for Great Blue Turacos and lowest for Black-billed Turacos. Most fruits eaten by turacos came from trees. Although most leaves eaten by Great Blue Turacos also came from trees, leaves eaten by Ruwenzori Turacos mainly came from lianas and epiphytes. For the Ruwenzori and Black-billed turacos, the two territorial species, monthly dietary diversity increased with increasing fruit abundance in the environment, but this relationship did not hold for Great Blue Turacos. During periods of fruit scarcity, all three species depended more heavily on their most frequently used foods; this trend was particularly evident in the two territorial species. Like most frugivores, these turacos probably were generalists that exploited a great variety of fruit sources. Received 24 June 1996, accepted 24 January 1997. TURACOS (FAMILY MUSOPHAGIDAE) are large birds endemic to woodland and forested habitats of sub-Saharan Africa and are considered to be principally frugivorous (Brosset and Fry 1988). Given their large body size and potentially frugivorous habits, forest turacos may be important seed dispersers in African tropical forests. However, the ecology of most turacos is poorly known (Dowsett-Lemaire 1983, 1990; Candy 1984; Brosset and Erard 1986; Brosset and Fry 1988). Here, we examine the foraging ecology of three sympatric turacos in a tropical montane forest in Rwanda. Three species of turacos occur in the Nyungwe Forest Reserve, Rwanda. The Great Blue Turaco (Corythaeola cristata) exists throughout the entire elevational range of the forest (1,760 to 2,950 m; Dowsett-Lemaire 1990). The Ruwenzori Turaco (Musophaga johnstoni) is common between 2,000 and 2,920 m and may descend to 1,800 m in some wetter areas (J.-P. Vande Weghe pers. comm., C. Sun pers. obs.). The Black-billed Turaco (Tauraco schuettii) is found up to 2,500 m but is more abundant at lower elevations and reaches the lowest limit of the forest (Dowsett-Lemaire 1990, C. Sun pers. obs.). In this paper we compare the foraging I Present address: Department of Plant Pathology, University of Wisconsin, Madison, Wisconsin 53706, USA. E-mail: csun@macc.wisc.edu ecology of these turacos between 2,000 and 2,500 m, where they coexist. Specifically, we address the following: (1) What is the diet composition for each species of turaco? (2) What is the dietary response of each species to temporal changes in resource abundance in the environment?