Rivers are fundamental features in the Amazonian biogeography. Despite that, specialization by birds in river-created habitats seems to have been under-appraised in most of biogeographical studies and synthesis. River-created habitats comprise a complex mosaic of forests and other vegetation types at distinct stages of succession, with variations related to river color or type. Extending almost linearly along rivers and covering more than 15% of the Amazon basin, these habitats shelter a rich avifauna, with more than 100 specialized or exclusive species. In this thesis, we investigated how Amazonian floodplain birds are distributed. In the first chapter, we set out to test the power of the “color” of rivers in predicting differences in the avifauna among sites in the Rio Negro basin. Based in bird standardized surveys at distinct tributaries, we showed species compositions were significantly distinct between black- and whitewater rivers. Several indicators species supported distinctions and the water type of the rivers arose as a first factor to understand general range patterns for floodplain specialized birds. On the other hand, “intermediary” avifaunas were found at some sites; and in the second chapter, we investigated if and how the confluence with Rio Branco, affects the avifauna along Rio Negro itself, which is the world’s largest blackwater river. We sampled islands and riverbanks along the middle and the lower Rio Negro, above and below, respectively the confluence with the Rio Branco, and compared with sampling from the Rio Branco itself. These surveys indicated a combination of avifaunas, with higher richness below the confluence. Moreover, overall variation in species composition along the confluence was correlated with distinct levels of sediment concentration in the water (a proxy for water type), supporting the importance of this factor to the occurrence of birds in the floodplains. This phenomenon, involving waters and avifaunas, expressed the potential multiple roles (isolating, connecting and maintaining habitats) of the several confluences between large Amazonian rivers of distinct water types on the distribution of floodplain biodiversity. Finally, in the third chapter, we reviewed and analyzed geographic distributions of floodplain specialized bird species. Occurrence data on an updated list of specialized taxa supported at least eleven potential specific areas of endemism, essentially distinct from large interfluvial areas that are valid for terra firme birds. A parallel subdivision of Amazonia with at least nine regions, based solely on the distributions of floodplain specialized birds emerged as an alternative background for evolutionary studies and conservation of the floodplains biodiversity. From a conservation perspective, the dependency of the avifauna on micro-habitats that are geographically restrict implies high vulnerability for floodplain specialists. Although large tracts of river-created habitats are covered by protected areas, populations of floodplain specialized birds are vulnerable given the plans of damming several Amazonian rivers, which might alter the formation and availability of these micro-habitats. In synthesis, this thesis expresses the biogeographic specificities for Amazonian floodplains. Range patterns for specialized birds reflect broadly the ecological distinctiveness and the complex history of rivers draining different regions. River-created habitats offer interesting opportunities to a better understanding of the richness and evolution of the Amazonian avifauna and total biodiversity.
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