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VERVOORT R (2019) The Sahel: a paradise for Ruff Calidris pugnax?. LIMOSA 92 (3): 164-174.

Large numbers of Palaearctic waterbirds spend the northern winter in the Sahel. Ruff is the most abundant wintering wader in this narrow zone south of the Sahara. Most Ruffs arrive in August during the local rain season, attracted by thousands of rain-fed pools and small isolated lakes. These small wetlands are threatened, yet their significance for survival of the global Ruff population is not clear. Large rivers with seasonal flow originate in mountains south of the Sahel. Later in the season, they form large inundation zones in the Senegal Delta, Inner Niger Delta and Lake Chad basin. Specific climatologic and hydrologic conditions result in dynamic seasonally productive wetlands which support hundreds of thousands of waterbirds, including Ruffs. Waders follow receding floods, which leave a mosaic of temporary pools.
Ruff densities are highest in open shallow water, where they exploit various food resources. They switch from insects early in the season to natural seeds during flood recession. Ruffs also feed in large flocks on cultivated rice spilt during harvest. Daily time spent foraging can decrease to just 3 hours in cultivated rice fields, but Ruffs largely avoid intensively managed, large-scale irrigated rice cultures. In the central lakes of the Inner Niger Delta, molluscs are an abundant prey at a later stage of flood recession.
Early in February male Ruffs start fattening up for migration, gaining 1% of weight daily. After five weeks they are ready for migration across the Sahara and Mediterranean Sea. Females start fattening up and leave Africa about three weeks later than males. Since Ruffs are highly dependent on water, dry years are challenging, especially to females. Even in a wetland as large as the Inner Niger Delta, Ruffs can get trapped by drought, unable to get ready for migration, a risk exacerbated by the construction of dams.
In the Senegal Delta the flood recedes earlier than in the other floodplains in West-Africa. Furthermore, it is most affected by dams built for hydroelectricity and irrigation, resulting in loss of nearly all natural floodplains. Harvested irrigated rice cultures have been a substitute foraging habitat for Ruffs since the seventies, but only during a part of the season. Nowadays almost no Ruffs winter in the Senegal Delta, whereas in the seventies and eighties hundreds of thousands were counted. In the Lake Chad basin counts of wintering Ruffs have been increasing following the decline in the seventies and eighties, possibly because the size of the flooded area increased after the North and South basin of the lake became separated. The flood flowing through the Hadejia-Nguru and WazaLogone wetlands reaches Lake Chad late in the season, providing suitable habitat over the entire dry season.
It is unlikely that the large number of Ruffs caught for human consumption in the Inner Niger Delta is sustainable. Relatively stable numbers of Ruff counted in this delta may be explained by recruitment of birds from neighboring wetlands: the severe decline in the Senegal Delta could therefore have consequences for the Inner Niger Delta in the near future.
Two biogeographical populations of Ruff have been recognized, differing in wintering area: the West-African and the East-African/Indian populations. Although mixing in the breeding range, the western and eastern populations tend to breed more in the west or in the east of the breeding range, respectively. Also within the West-African population, a west to east preference in spring staging area may reflect wintering origin. Thus, reduced flooding in the Senegal Delta and hunting in the Inner Niger Delta may have contributed to the decline of the north western breeding population, whereas increased flooding in the Lake Chad basin may have contributed to the increase of West-Siberian breeding birds, respectively

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limosa 92.3 2019
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