| INTRODUC TI ONOne of Amazonia's most striking features is the diversity of "colors" of its many rivers. The distinction between white-, black-, and clearwater rivers was recognized by early naturalists in the Amazon basin (e.g., Wallace, 1853; Holdridge, 1933) and long before them in the very names of the rivers, such as "Rio Negro" and "Rio Branco." River "color" (i.e., river type; hereafter used interchangeably) classification is based on the color and other physical and chemical parameters of the water, which in turn are related to the geomorphology of the river's catchment region (Sioli, 1968;Janzen, 1974). Turbid and nutrient-rich whitewater rivers (e.g., Rio Madeira) mostly drain the Abstract Despite the importance of rivers in Amazonian biogeography, avian distribution patterns in river-created habitats (i.e., floodplain forests) have been sparsely addressed.Here, we explore geographic variation in floodplain forest avifaunas, specifically regarding one of the most striking aspects of the Amazon: the diversity of river "colors" (i.e., types, based on the color of the water). We sampled the avifauna at 30 sites, located in 17 different rivers (nine black-and eight whitewater), in the Rio Negro basin, northwestern Brazil. Our sampling comprised ten 15-min point-counts per site, distributed every 500-1000 m along the river. We recorded a total of 352 bird species, many of which occurred in both river types. Although bird species richness was similar among rivers, we found significant differences in species composition. Nearly 14 percent of the species were significantly associated with one or the other river type. Most floodplain forest specialists occurred predominantly in whitewater rivers, whereas species that are typically associated with white-sand habitats occurred in blackwater. Despite significant distinctions between river types, occurrence patterns and levels of habitat association differed among indicator species and may vary in the same species throughout its global distribution. There were also "intermediate" avifauna in some of our sites, suggesting that continuous parameters characterizing river types structure species turnover. The water color-based classification of Amazonian rivers represents a simple and powerful predictor of the floodplain forest avifauna, offering a stimulating starting point for understanding patterns of floodplain bird distributions and for prioritizing conservation efforts in these overlooked habitats.Abstract in Portuguese is available with online material. K E Y

SummaryThe Rio Branco is a river with unique biogeographic and ecological features, threatened by the Brazilian Government’s plan to build a major hydroelectric dam and associated hydroway along its course. The river crosses one of Amazonia’s largest rainfall gradients and a major geomorphological boundary along a savanna/forest ecotone, marked by the Bem Querer rapids. Above the rapids, the upper Rio Branco runs through the Boa Vista sedimentary formation and crosses the crystalline rocks of the Guiana Shield, and its margins are flanked by gallery forests. Downriver, it runs through a low-lying sedimentary basin, with Amazonian floodplain forests along its margins. Here, we present the results of ∼ 15 years of ornithological research on the Branco and its major tributaries, providing baseline data and evaluating potential threats to the riverine avifauna. Our surveys included opportunistic observations and standardized surveys along the entire length of the river in 16 systematically distributed localities. We catalogued 439 bird species, 87% of which are documented by physical evidence (specimens, recordings, photographs). Forty-six percent are restricted to single habitats, suggesting a high degree of habitat specialisation. A third of the species are widely distributed along the river, whereas 45% are restricted to either the upper or the lower Rio Branco, including 40 and 30 Indicator Species, respectively. Twenty-five species are threatened at global or national levels, including two ‘Critically Endangered’, nine ‘Vulnerable’, and 14 ‘Near Threatened’. We present a list of 50 bird species that are candidates for monitoring studies. Threats to the avifauna from dam construction include permanent flooding above the dam, eliminating gallery forests, river islands, and sandy beaches, and the disruption of the flood pulse along the river, affecting river island and floodplain forest specialists, many of which are globally threatened with extinction. If built, the Bem Querer dam will wipe out the ecotone region and affect dramatically the river’s avifauna.

Aim Although ‘river color’ or water type is an important determinant of Amazonian floodplain biodiversity, the relevance of mixing distinct water types at river confluences to the distribution of terrestrial floodplain fauna has been largely overlooked. We investigated how the influx of a sediment‐rich whitewater tributary affects the floodplain forest avifauna along the world's largest blackwater river. Location Northwestern Brazilian Amazon. Taxon Birds. Methods We sampled floodplain avifauna and retrieved estimates of sediment concentration in the water (the main parameter in river‐water classification) at 52 sites, along the Negro (blackwater) and Branco (whitewater) rivers, above and below their confluence. We compared species richness and composition using analyses of variance, ordinations, generalized linear models and indicator species analyses. Results Bird species composition on the lower Rio Negro (below the confluence) was distinct from both the upper Negro (above the confluence) and the Branco, and species richness on the Negro increased below the confluence. Typical whitewater bird species occurring on the Branco were found exclusively or predominantly along the left side of the lower Rio Negro, where the Branco's muddy waters seem to be channelled. Overall avian compositional variation among sites was correlated with sediment concentration in the water, a determinant of floodplain forest structure. Main conclusions The influx of the muddy waters of the Rio Branco into the Rio Negro promotes the co‐occurrence of bird species that are segregated by river type upstream, increasing species richness at the landscape scale. Rather than just representing a potential blackwater barrier between whitewater systems, the lower Rio Negro comprises a unique biogeographical transition zone, with a mixed avifauna occurring in a mosaic of varied floodplain forest types. Our results suggest that confluences of large rivers of distinct water types represent a significant factor determining species distributional boundaries and geographic patterns of Amazonian floodplain biodiversity.

In the Brazilian Amazon, two monospecific genera, the Harpy Eagle and Crested Eagle have low densities and are classified by IUCN as Near Threatened due to habitat loss, deforestation, habitat degradation and hunting. In this study, we evaluate occurrence of these large raptors using the environmental surveys database from Belo Monte Hydroelectric Power Plant. Integrating the dataset from two methods, we plotted a distribution map along the Xingu River, including records over a 276-km stretch of river. Terrestrial surveys (RAPELD method) were more efficient for detecting large raptors than standardized aquatic surveys, although the latter were complementary in areas without modules. About 53% of the records were obtained during activities of wildlife rescue/flushing, vegetation suppression or in transit. Between 2012 and 2014, four Harpy Eagles were removed from the wild; two shooting victims, one injured by collision with power lines and one hit by a vehicle. Also, seven nests were mapped. The mean distance between Harpy Eagle records was 15 km along the river channel, with a mean of 20 km between nests near the channel, which allowed us to estimate 20 possible pairs using the alluvial forest, riverine forest and forest fragments. Territories of another ten pairs will probably be affected by inundation of the Volta Grande channel, which is far from the main river. The average distance between Crested Eagle records was 16 km along the river channel. The only nest found was 1.3 km away from a Harpy Eagle nest. The remnant forests are under threat of being replaced by cattle pastures, so we recommend that permanently protected riparian vegetation borders (APP) be guaranteed, and that forest fragments within 5 km of the river be conserved to maintain eagle populations.Keywords: neotropical raptors, Amazon, hydroelectric power plant, environmental impact, Accipitridae. Abundância de Gavião-real e Gavião-real falso numa área sob impacto de reservatório no Baixo e Médio rio XinguResumo Na Amazônia brasileira dois gêneros mono-específicos, Harpia e Morphnus, caracterizam-se por baixa densidade e estão classificados pelo IUCN como Quase Ameaçados, porém ocorrem sobre grande parte do território nacional, suas principais ameaças são a fragmentação florestal, a degradação de hábitat e a caça. Neste estudo avaliamos a abundância destas duas grandes aves de rapina utilizando a base de dados dos programas ambientais da UHE BeloBraz.

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Aim: To investigate the influence of bioclimatic, productivity and topographic variables on avian diversity patterns in riparian habitats along a savanna/humid forest environmental gradient. We investigate how this gradient affects patterns of taxonomic and phylogenetic alpha and beta diversities, and whether the changes observed along the river are the result of taxonomic (and phylogenetic) replacement or nestednessresultant dissimilarities. We also explore a potential ecological mechanism to account for differences in species richness along the gradient. Location: Basin of the Rio Branco, northern Amazonia, Brazil. Taxa: An avian community of 325 bird species. Methods: We sampled avian communities using standardized avian point counts at 16 localities, systematically distributed along the Rio Branco and two of its major tributaries. We compared patterns of species richness using rarefied numbers of species detected, and patterns of phylogenetic diversity with a community-wide consensus tree. In addition, we partitioned beta diversity in species replacement and nestedness-resultant dissimilarities. We reduced predictor variables using a principal components analysis, correlating locality scores with changes in diversity. We tested the effect of climatic variables on beta diversity with a distance-based redundancy analysis (dbRDA). Results: Patterns of avian composition and species richness were highly correlated with climatic and productivity variables. We found more bird species in less arid localities with higher annual precipitation, and in areas with lower annual temperatures, lower evapotranspiration and less temperature variation throughout the year. Despite differences in species richness, the number of individuals remained relatively similar along the gradient. However, species-rich localities presented lower average species frequency and median avian biomass. Patterns of taxonomic and phylogenetic beta diversity were correlated with the climatic gradient and were due to species replacements. Main conclusions: Climate represents a major player in structuring avian communities along the Rio Branco, affecting distinct levels of avian diversity organization. We found evidence of species packing, a mechanism to fit more species in the communities. Patterns of species replacement highlight the importance of transitional zones | 2329 NAKA et Al.

Aim Amazonian floodplains include distinct types of seasonally flooded habitats, determined by the flooding regime and sedimentation dynamics. Some bird species prefer specific habitat types within the floodplains. To investigate whether distinct habitats are differentially affected by geologic and climatic history, we compare population history in a sympatric and closely related pair of ovenbird species with different habitat associations. Location Amazonian floodplains. Taxa Synallaxis albigularis and Mazaria propinqua (Aves; Furnariidae). Methods Occurrence records were obtained from museums and public databases. Genomic data included nuclear loci (UCE) and the mitogenome for 49 samples. SNPs from UCE data were used to infer population genetic structure and effective migration. Mitogenomes were used to build phylogenetic trees and chronograms. Both datasets were used to infer historical demographic changes and test demographic scenarios. Results S. albigularis includes geographically structured mtDNA clades with a crown age of 250 ka, whereas M. propinqua includes a single clade with a crown age of 38 ka. Effective migration is lower at the base of the Andes for S. albigularis and at the lower Negro River for M. propinqua. Population expansion is detected for both species during the Quaternary, but was steeper and more recent in M. propinqua. Main conclusions The differences in population histories relate to distinct habitat associations along Amazonian floodplains. Preference of M. propinqua for more ephemeral island habitats may favour local extinctions, leading to demographic change, low genetic variability, no population structure and smaller effective population size. In contrast, more resilient habitats along the floodplains inhabited by S. albigularis may sustain local populations, generating and maintaining local diversity. Our results suggest that climatic variations of the late Pleistocene and Holocene caused changes in distribution and connectivity of the different types of habitats along the Amazonian floodplains, affecting gene flow and population sizes of associated bird populations.

The annual flooding in the Amazon basin transforms the understory of floodplain forests into an aquatic environment. However, a great number of non-aquatic bird species occupy the understory and midstory of these forests. In general, these birds are thought to be sedentary and territorial, but the way they adapt to this dramatic seasonal transformation has never been described in detail. In this study, we describe avifaunal strategies to cope with seasonal flooding in the lower Purus region, central Amazonia, Brazil. We conducted focal observations of five insectivorous species occupying the lowest forest strata in two types of floodplain forest (black- and whitewater) during the low- and high-water seasons. For each observation, the height of the bird above the substrate (ground or water), its vertical position in the forest, and vegetation density around the bird were noted. All species remained present in the floodplain forests during the two seasons and were not recorded in adjacent unflooded (terra firme) forest. In general, birds migrated vertically to higher forest strata and most species (three of the five) occupied similar vegetation densities independent of water level. Despite the tendency of all species to rise in relative vertical position at high water, there was a reduction in height above substrate for four of the five species, suggesting that their position relative to water was not an important microhabitat element for them. Responses were similar in the two floodplain forest types. It is likely that the decrease in available space during the flood, combined with similar vertical displacement in arthropods, leads to increased prey density for understory insectivorous birds and permits year-round territoriality without major habitat shifts.