We studied spatial and temporal variation in a population of Sulawesi
Red-knobbed Hornbills (Aceros cassidix) in relation to availability of
fruit resources over a two-year period in the Tangkoko DuaSudara Natu
re Reserve, North Sulawesi, Indonesia. Fruit production did not show a
ny discernable patterns over 22 months of study, in spite of the stron
g seasonality of rainfall. Figs were available in all months of the ye
ar, and fig biomass exceeded ripe nonfig-fruit biomass in 10 of 22 mon
ths. Hornbill densities fluctuated dramatically over time ((x) over ba
r = 51 birds . km(-2), range 9.3-82.7) and among habitats. Spatial and
temporal variation in hornbill numbers was best explained by habitat
selection and the abundance and distribution of figs. Hornbill numbers
were higher in those areas with greater densities of fig trees, and m
onthly hornbill densities and mean nock size increased with increasing
fig biomass. Because Sulawesi Red-knobbed Hornbills appear to track f
ig production over potentially large distances, and include a mix of o
ther rainforest tree species in their diet, we hypothesize that they m
ay play an important role as agents of rainforest regeneration.