The effects of fruit availability and habitat disturbance on an assemblage of Sumatran hornbills

Abstract

We examined the influence of fruit availability and habitat disturbance, including past and recent forest fires, on an assemblage of hornbills over a four-month period in the Bukit Barisan Selatan National Park, Sumatra. The assemblage is dominated by Wreathed Hornbills Aceros undulatus (7.5 birds/km2), followed by Bushy-crested Hornbills Anorrhinus galeritus (3.05 birds/km2), Rhinoceros Hornbills Buceros rhinoceros (2.6 birds/km2), and Helmeted Hornbills Buceros vigil (1.9 birds/km2). Overall densities for each species were consistent with estimates from other South-East Asian sites but densities varied temporally and spatially, even for territorial species. We speculate that Rhinoceros and Helmeted Hornbills may exhibit facultative territoriality or they may not be territorial at this site. We found a positive relationship between temporal variability in hornbill numbers and the availability of ripe fruits. All hornbills, especially Rhinoceros and Bushy-crested Hornbills, tended to avoid highly disturbed areas; these areas had a lower than expected number of fruiting trees in five important hornbill diet families. Densities of Bushy-Crested, Rhinoceros, and Helmeted Hornbills declined from 28 to 63% in the post-burn surveys. Wreathed Hornbills, however, increased slightly in the post-burn surveys, possibly because they were nesting there at the time. Movement of hornbills between disturbed and primary forest habitat may enhance regeneration of disturbed areas if hornbills are transporting viable seeds.