Contribution of River-Created Habitats to Bird Species Richness in Amazonia

Abstract

A substantial portion (15%) of the non-aquatic avifauna of the Amazon Basin is restricted to habitats created by rivers. These habitats are divided into six categories: beaches and sandbars, sandbar scrub, river edge forest, varzea forest, transitional forest, and water-edge. Lists of species restricted to these habitats are presented; for many of these species, this is the first published information on habitat preferences. As many as 169 bird species in the lowland neotropics may have evolved in Amazonian rivercreated habitats, with 99 of these spreading secondarily to man-made second-growth or to regions outside the Amazon Basin. Neither the Congo or Mississippi basin avifaunas show such a high percent of species restricted to river-created habitats; this difference is almost certainly due to the greater amplitude of seasonal water level fluctuations of the Amazon River and its tributaries and consequent greater extent of riverine habitats. Alteration of seasonal water flow patterns that would destroy these habitats could potentially exterminate 64 species of Amazonian river-created habitat specialists. The use of mist nets to sample bird community composition is discussed. NOWHERE IN THE WORLD IS BIRD SPECIES RICHNESS greater than in the Amazon River basin, both in terms of species inhabiting the region as a whole (Amadon 1973) and coexisting at any given point (Pearson 1977). In comparison with temperate regions, year-round availability of fruit and flowers (Orians 1969, Karr 1971) and very large insects (Schoener and Janzen 1968, Schoener 1971) account for much of the high alpha-diversity in the tropics, with smaller contributions from resources such as army ants (Willis and Oniki 1978), bamboo thickets (Parker and Remsen, ms.), and special foraging substrates (Orians 1969, Terborgh 1980). The large number of Pleistocene refugia within and adjacent to the Amazon Basin (Haffer 1969, 1974; Terborgh 1980) may also contribute to the high regional diversity. The purpose of this paper is to point out the contribution of river-created habitats, developed to a much greater extent in Amazonia than anywhere in the world, to regional diversity of Amazonian