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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