To help fill the gap in detailed knowledge of avian community structure in tropical forests, we undertook a census of a 97 -ha plot of floodplain forest in Amazonian Peru. The plot was censused over a 3-mo period spanning the 1982 breeding season. The cooperative venture entailed ::::::12 person-months of effort. Conventional spot-mapping was the principal method used, but several additional methods were required to estimate the numbers of non-territorial and group-living species: direct counts of the members of mixed flocks, saturation mist-netting of the entire plot, opportunistic visual registrations at fruiting trees, determination of the average size of parrot flocks, color banding of colonial icterids, etc.Two hundred forty-five resident species were found to hold territories on the plot, or to occupy all or part of it. Seventy-four additional species were detected as occasional-tofrequent visitors, wanderers from other habitats, or as migrants from both hemispheres. By superimposing territory maps or the areas of occupancy of individual species, we determined that point (alpha) diversities exceeded 160 species in portions of the plot. About 1910 individual birds nested in 100 ha of this floodplain forest, making up a biomass conservatively estimated at 190 kglkm 2 • The total number ofbreeding birds was equivalent to that in many temperate forests, but the biomass was about five times as great. Predominantly terrestrial granivores contributed the largest component of the biomass (39%), followed by largely arboreal frugivores (22%). Considering only insectivores, the biomass (34 kg!km 2 ) is somewhat less than that in the forest at Hubbard Brook, New Hampshire (40 kg!km 2 ), although it is greater (55 kglkm 2 ) if one includes omnivores. The number of insectivores was considerably less than at Hubbard Brook, due to their 60% larger average body size (32 vs. 20 g).Even though a large majority of the species were patchily distributed, the 97 -ha plot was found to include 99% of the bird species that regularly occupy mature floodplain forest at Cocha Cashu. The most abundant species occupied territories of 4-5 ha, and 84 species (26%) had population densities of :o; 1 pair per square kilometre. Of these, 33 (10% of the total community) were judged to be constitutively rare (i.e., having low population densities everywhere), rather than being merely locally rare. Many of these are predicted to be vulnerable to forest fragmentation and disturbance. Comparison of these results with those from other tropical forests proved difficult due to a lack of standardized methodology.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The Association for Tropical Biology and Conservation is collaborating with JSTOR to digitize, preserve and extend access to Biotropica. 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.

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At least 11 species of birds in northern Bolivia and southern Peru are dead-leaf-searching "specialists": more than 7 5% of our foraging observations of these species have been of individuals searching for insects in dead, curled leaves suspended above ground in the vegetation. All known specialists of this kind belong to the families Furnariidae and Formicariidae. An additional six species, here called "regular users," exhibit dead-leaf-searching behavior in 25% to 75% of our foraging records. The number of specialists and regular users decreases with rising elevation in the Andes. Specialists disappear from the gradient between 2,000 m and 2,575 m, but regular users occur as high as 3,300 m, near timberline. As many as eight species of dead-leaf-searching specialists coexist in western Amazonia.