Disturbed habitats may continue to lose species long
after disturbance through a process of “extinction debt (Tilman et al. 2002). It is unclear whether the avifauna
of the islands we studied has reached relaxation (i.e., already
lost all sensitive species). The precise chronology
of forest loss on the islands is unknown. Because avifaunas
in fragmented forests may take up to 100 years to
relax (Brooks et al. 1999b), it is probable that more extinctions
may occur on these islands even without any
further forest disturbance. Because we did not estimate
the population sizes of birds on the islands, we cannot
predict with our data which of the remaining species are
most threatened due to small population size.
Our results suggest that deforestation poses a threat
to the persistence of forest birds in Southeast Asia (see
also Brooks et al. 1997, 1999a), although the relation
between percent deforestation and species loss was not
statistically strong because our historical sampling data
were limited. Yet some forest species (on Bintan, e.g.,
Black-naped Monarch [Hypothymis azurea]) persisted
on the islands despite deforestation, although it is unclear
how viable their populations are. On some of the
islands, hunting is a formidable threat (e.g., Bintan) and
may extirpate even the most resilient forest species. Due
to lack of data, however, we are not sure whether hunting
affected extinctions on the islands