“Very Small” Bird Populations in Amazonia

Abstract

In view of the vast, limitless expanse of the Amazonian rainforest region, the title of this chapter may appear as a contradiction in itself. However, there are a number of Amazonian habitat types with a conspicuously patchy distribution, where several ecological specialist bird species, as well as other animals, form fairly small and widely separated populations. On the other hand, most rainforest birds of the Amazon basin indeed form large and more or less continuously distributed populations which occupy large areas, although population densities are very low. This has been known in general terms for a long time, but quantitative data of population densities have been obtained only in recent years (Terborgh 1986; Bierregaard and Lovejoy 1989, Terborgh et al. 1990). Among a total of 215 and 145 forest birds studied at two rainforest sites in upper and central Amazonia, respectively, most species were rare, only few species were common and conspicuous. In the upper Amazonian bird community, median abundance was 2.5 pairs per km², 84 species had population densities of ≤ 1 pair per km² (Terborgh et al. 1990).