Mechanisms of avian population decline and species loss in tropical forest fragments

Even large fragments of tropical forest lose bird species over time. The speed of disappearance and permanence of these losses depend on a variety of factors, but the pattern of species loss appears more universal. We still do not understand the degree to which different mechanisms lead to population declines and local extinction in fragmented tropical landscapes. We review data currently available to evaluate three of the leading hypotheses, which include altered community dynamics producing mesopredator release and indirect effects of elevated herbivore populations; sensitivity of forest birds to altered microclimatic conditions in fragments, and the constraint of poor dispersal ability that reduces connectivity in fragmented landscapes. We find that all three mechanisms require additional study and suggest steps to be taken in future studies.