Over a ten-year period, each December the same observer counted waterbirds on the same stretch of the Kariega River in the Eastern Cape, South Africa. The site surveyed is dominated by waders, with variable numbers of other feeding guilds. Piscivorous birds in particular are poorly represented. Differences in the numbers of birds and species recorded, both within a single month and between years, are only partly explicable by environmental conditions on this permanently open estuary. From our comparison with nearby sites, we conclude local movements between rivers and pans in the region must occur regularly over short time intervals.

中文翻译：

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数度假中的水鸟：东开普河口的快照

在十年的时间里，每年的12月，同一位观察员在南非东开普省Kariega河的同一条河段上数出水鸟。所调查的地点以涉水为主，其他行会的数量也不尽相同。食肉鸟的代表性很差。在这个永久开放的河口上，环境条件只能部分解释一个月内以及几年之间记录的鸟类和物种数量的差异。通过与附近站点的比较，我们得出结论，该区域河流和平底锅之间的局部运动必须在短时间内定期发生。