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.

中文翻译：

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里约布兰科的鸟类区系，一个处于危险中的亚马逊进化和生态热点

总结 Rio Branco 是一条具有独特的生物地理和生态特征的河流，受到巴西政府计划在其沿线建造大型水电大坝和相关水道的威胁。这条河穿过亚马逊流域最大的降雨梯度之一和沿着以本奎勒急流为标志的稀树草原/森林交错带的主要地貌边界。在急流之上，Rio Branco 上游穿过 Boa Vista 沉积地层，穿过圭亚那地盾的结晶岩，其边缘两侧是画廊森林。在下游，它穿过一个低洼的沉积盆地，其边缘有亚马逊河漫滩森林。在这里，我们展示了对布兰科河及其主要支流进行了 15 年的鸟类学研究的结果，提供基线数据并评估对河流鸟类的潜在威胁。我们的调查包括在 16 个系统分布的地点沿河流全长进行机会性观察和标准化调查。我们对 439 种鸟类进行了编目，其中 87% 有物证（标本、录音、照片）记录。46% 仅限于单一栖息地，表明栖息地高度专业化。三分之一的物种广泛分布在河流沿岸，而 45% 的物种仅限于 Rio Branco 上游或下游，分别包括 40 和 30 个指示物种。25 个物种在全球或国家层面受到威胁，包括 2 个“极度濒危”、9 个“易危”和 14 个“近危”。我们列出了 50 种候选鸟类进行监测研究。大坝建设对鸟类的威胁包括大坝上方的永久性洪水，消除了廊道森林、河岛和沙滩，以及沿河的洪水脉冲中断，影响河岛和洪泛区森林专家，其中许多受到全球威胁随着灭绝。如果建成，Bem Querer 大坝将消灭生态交错带地区，并显着影响河流的鸟类动物群。