Differences in Foraging Ecology between Generalized and Specialized Frugivorous Birds in the Fushan Experimental Forest, Northeastern Taiwan

Abstract

In order to distinguish differences in foraging between generalized and specialized frugivores, we studied the foraging ecology of 3 commonly seen fruit-eating birds (Gray-cheeked Fulvetta Al-cippe morrisonia morrisonia, Black Bulbul Hypsipetes madagascariensis nigerrimus, and Blackbrowed Barbet Megalaima oorti nuchalis) in Fushan Experimental Forest, northeastern Taiwan. From June 1997 to May 1998, the foraging behaviors, species of fruit eaten, and habitat characteristics of these 3 species were recorded monthly. Habitat variables included vegetation level, vegetation density, foraging height, plant height, and diameter at breast height (dbh) of the fruiting plant. In terms of foraging behavior, gleaning and reaching were used frequently by all 3 species to obtain fruit; however, the Black-browed Barbet used much more reaching than gleaning. On the other hand, the Black Bulbul also used sallying to snatch fruit, and the Gray-cheeked Fulvetta was seen to hang at times. The Black-browed Barbet and Black Bulbul predominantly foraged high in the canopy (＞ 70% of the time) for drupes and berries, while the Gray-cheeked Fulvetta spent more time foraging in the understory (52.3%) and consumed a greater diversity of fruit types than the other 2 species. In addition, the Black-browed Barbet and Black Bulbul concentrated their foraging in large fruiting trees, whereas the Gray-cheeked Fulvetta took fruit mainly from smaller and thinner trees or bushes. As a result, the Gray-cheeked Fulvetta, a generalized frugivore, not only exhibited greater niche breadth in terms of fruit type and vegetation level, but also expressed a wider variation in foraging habitat use than did the specialized frugivores, the Black Bulbul and Blackbrowed Barbet. This study showed that specialized frugivores use a far more select set of fruits, fruiting plants, and habitats than do generalized frugivores.