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The Orange River avifauna: abundance, richness and comparisons

机译：奥兰治河航空动物：丰富，丰富和比较

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Like many other southern African rivers, the avifaunal richness and abundance of the Orange River, southern Africa's longest, remains virtually unknown. Given that the Orange River runs through hyper-arid regions in its lower reaches, its linear oasis effect and its role as a reservoir for Red Data bird species is likely but has not been quantified. Two surveys either side of the border town of Noordoewer, in the rainy and dry seasons of 1996 and 1997 determined that species richness was higher in riverine habitat (71 species) than in the surrounding Nama Karoo (46 species) confirming the linear oasis effect. Surveys revealed five Namibian Red Data species. Peregrine Falcons, Falco peregrinus, and African Fish Eagles, Holiaeetus vocifer, were relatively common while the endangered Cape Eagle Owl, Bubo capensis, occurred sporadically. Among wetland Red Data bird species, Black Storks, Ciconia nigra, occurred in less disturbed areas, and White-backed Night Herons, Gorsachius leuconotus, were an unexpected species at this locality. The overall species richness of 103 birds and a density of riparian birds of 31-34 birds/10 km, makes the lower Orange River avifauna similar to the Cunene River but tenfold less abundant than Namibia's other perennial. rivers. Despite the low diversity, the arid habitats of the lower Orange River support greater diversity than more easterly regions when all current surveys of richness and abundance from Lesotho to the mouth on the Namib coast are combined. This east-west trend may be explained by the slower flow and warmer water of the lower Orange River but natural turbidity and regulation may explain the generally low diversity and abundance indices. Major rivers in southern Africa appear to have been overlooked as wetland habitats, and further avifaunal surveys of all of them are recommended.
机译：像许多其他南部非洲河流一样，南部非洲最长的奥兰治河的航空丰富性和丰度实际上仍然未知。鉴于奥兰治河贯穿下游的高干旱地区，其线性绿洲效应及其作为红色数据鸟类物种的储存库的作用很可能但尚未量化。在1996年和1997年的雨季和干旱季节，在边境小镇Noordoewer两侧进行的两次调查确定，河岸生境（71种）的物种丰富度高于周围的Nama Karoo（46种），证实了线性绿洲效应。调查显示五种纳米比亚红色数据物种。百富勤猎鹰，per游eg和非洲鱼鹰（Holiaeetus vocifer）相对常见，而濒临灭绝的海角鹰Eagle（Bubo capensis）则偶发。在湿地红色数据鸟类物种中，黑鹳，黑鹳（Ciconia nigra）发生在受干扰较少的地区，而白背夜鹭（Gorsachius leuconotus）是该地区出乎意料的物种。共有103只鸟的物种丰富，河岸鸟的密度为31-34只鸟/ 10公里，这使得奥兰治河下游的鸟类类似于库内内河，但比纳米比亚的其他多年生动物少十倍。河流。尽管多样性低，但将当前所有从莱索托到纳米比亚海岸河口的丰富度和丰度调查相结合时，奥兰治河下游的干旱栖息地比东风地区具有更大的多样性。这种东西向的趋势可以用奥兰治河下游的水流较慢和水温较高来解释，但自然的浊度和调节性可以解释总体上较低的多样性和丰度指数。南部非洲的主要河流似乎已被忽视为湿地栖息地，因此建议对它们进行进一步的航空调查。

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