WYMENGA E, KLOP E & ZWARTS L (2019) The Sahel as a wintering area for migratory birds. LIMOSA 92 (3): 108-124.

One of the most dominant ecological features of West-Africa is the steep rainfall gradient when going from north to south. This is reflected in a wide variety of ecosystems and land use patterns. Over a distance of less than 1000 km, ecosystems change from arid deserts in the north to wet rainforests in the far south, with a broad savanna zone in between. Along this gradient the species richness of Palearctic migratory birds declines with increasing rainfall, and the highest number of these species is found in the Sahel, a semiarid zone that marks the transition from the desert to the savanna zones. Over 130 species of Palearctic migratory birds spend the northern winter in the Sahel, far more than in any of the other bioclimatic zones in the region. Roughly half of these species are dependent on wetland habitats, and major wetlands like the Inner Niger Delta, the Senegal Delta and the Waza-Logone area provide important habitat to many species of waterfowl, herons, waders and passerines.
Birds in the Sahel have to cope with major annual fluctuations in rainfall, which affects the availability of water and food and hence, the quality of their wintering grounds. This is clearly shown by e.g. the annual fluctuations in inundated area of the Inner Niger Delta in central Mali. Two other important factors that affect the quality of the wintering grounds for migratory birds, as well as the habitat of many other species, are the high growth rate of the human population and the concomitant changes in land use. Since the 1950s the human population has shown a fivefold increase from 73 to 370 million people and there is a high demand for land, water and energy. Agricultural development and the realization of dams for hydropower have locally resulted in major declines in the availability of water and floodplain habitat, whereas wood cutting, burning and high grazing pressure have shown their impact on tree cover. These changes can have manifold impact on migratory bird populations, including displacement and changes in survival rates, as is described in this and other papers in this special Limosa-edition.

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