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

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 Black-billed 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.