Nutritional Determinants of Diet in Three Turacos in a Tropical Montane Forest

Abstract

We studied nutritional characteristics of plants in the diets of three closely related, highly frugivorous turacos that inhabit a tropical montane forest in Rwanda: the Great Blue Turaco (Corythaeola cristata), the Ruwenzori Turaco (Musophaga johnstoni), and the Blackbilled Turaco (Tauraco schuettii). The first two species also consume leaves. We compared the physical properties and nutrient contents of fruits and leaves eaten by turacos with those of common but uneaten plant species. Concentrations of hexose sugars were higher in fruits eaten by turacos than in those not eaten. In contrast, concentrations of nitrogen and fatty acids were lower in fruits eaten by turacos than in those not eaten. Leaves of plant species eaten by turacos did not differ significantly in either nitrogen or fiber content from those uneaten. Factors other than nitrogen and fiber, perhaps including secondary defensive compounds, are likely to affect leaf choice by turacos. The Great Blue Turaco ate aquatic plants containing high levels of sodium. We hypothesize that the Great Blue Turaco (which is the most folivorous of the three species) eats aquatic plants with high levels of sodium to help detoxify plant secondary compounds.

Seed Dispersal, Seed Predation, and Seedling Recruitment of a Neotropical Montane Tree

“…The Lauraceae is an important family in Neotropical forests in terms of species richness, a food resource for birds, and economic value (Wheelwright 1983, 1985a, Burger and van der Werff 1990, Gentry 1990, Martínez-Ramos and Soto-Castro 1993, Guindon 1996. Members of the Lauraceae are also important dietary components for frugivorous birds in Africa, Southeast Asia, and Australia (Crome 1975, Snow 1981, Sun et al 1997. Ocotea endresiana Mez (listed as O. austinii in Wheelwright et al [1984], Wheelwright [1985aWheelwright [ , 1986) is a common canopy tree in montane forests in central and northwestern Costa Rica at 1100-2300 m elevation (Burger and van der Werff 1990).…”

Contrasting digestive strategies of fruit‐eating birds

“…Bird‐dispersed fruits typically contain either simple sugars (primarily glucose and fructose; Widdowson & McCance 1935) or lipids (Herrera 1987; White 1989; Eriksson & Ehrlén 1991; Witmer 1996a), and fruit‐eating birds vary in the proportions of sugary and lipid‐rich fruits in their natural diets (e.g. Bosque & Parra 1992; Fuentes 1994; Witmer 1996a; Sun, Moermond & Givnish 1997). Bird‐dispersed fruits have also been considered nutritionally limited in energy because of dilution of nutrients with indigestible seed bulk (Levey & Grajal 1991; but see Witmer 1998a), as well as protein because of the typically low nitrogen content of fruit pulp (Moermond & Denslow 1985).…”

Influence saisonnière des ressources alimentaires sur la distribution des touracos (Musophagidae) dans quelques milieux naturels du Centre et du Sud-est de la Côte d’Ivoire

“…Ainsi, la variation de l'abondance des touracos serait-elle liée aux différentes périodes de fructification des espèces végétales qu'ils exploitent. Les touracos consomment principalement des fruits, ce sont donc des espèces frugivores (Sun et al, 1997). Cependant, ils consomment d'autres organes végétaux tels que les feuilles et les bourgeons.…”

“…La distribution des touracos n'est pas liée à une essence végétale. Les touracos sont des espèces généralistes qui exploitent une large gamme d'espèces végétales (Sun et Moermond (1997). Cependant, les touracos sont fortement associés à certaines espèces végétales dont ils apprécient les fruits.…”

“…Divers facteurs notamment les ressources alimentaires conditionnent la présence d'une espèce dans un milieu (Keitt et al, 2002). Les touracos (Musophagidae) sont des espèces arboricoles et frugivores qui sont importantes pour la biodiversité, du fait de leur rôle dans la dispersion des graines (Sun et Moermond, 1997). Malgré cette importance, l'écologie alimentaire des touracos dans les milieux naturels est peu documentée (Borghesio, 1997).…”