Aspects of diet choice and digestion in the Dark-capped Bulbul Pycnonotus barbatus

Abstract

Most avian frugivores are not specialised and feed on a variety of fruit that are generally nutrient dilute. Little is known about avian frugivores that supplement their diets with insects as a nutrient source. Although considered a frugivore, the Darkcapped Bulbul Pycnonotus barbatus feeds on insects opportunistically. Consequently food preference, intake rates and digestive efficiencies were compared on a nutrient-dilute fruit diet (apple) versus an insect diet (mealworm) and a combination of these. Transit times were also determined. Birds maintained body mass on the apple-only treatment but gained body mass on the mealworm and combination treatments. The apparent energy-assimilation coefficient varied significantly between treatments, being highest on the mealworm diet. Energy intake rates were higher on the mealworm diet. When offered a combination, birds chose mealworms in preference to apple and ate little apple. The results suggest that these frugivorous birds obtain adequate nutrients for maintenance from nutrient-dilute fruit but supplement their diet with insects or nutrient-dense fruit to obtain nutrients required for activities additional to maintenance.

Ostrich 2008, 79(1): 73–78