Loess and Bee-Eaters II: The 'loess' of North Africa and the nesting behaviour of the Northern Carmine Bee-Eater (Merops nubicus Gmelin 1788)
Abstrakt
The Northern Carmine Bee-Eater (Merops nubicus) lives and breeds in a well demarcated region stretching across Africa close to the 15 degrees N line of latitude. The Bee-Eater zone appears to be associated with a band of loess, defined by Scheidig on his 1934 map as second-order loess.
Bee-eaters are known to favour loess for nesting tunnels and it appears that the 15 degrees N material is sufficiently loess-like. Obvious sources for particulate materials for the 15 degrees N band are the Fonta-Djalon highlands which supply sedimentary material to the River Niger; the Bodele Depression, the deepest part of Lake Megachad, source of dust for the World; the Ethiopian highlands at the eastern end of 15 degrees N which supply silt to the Nile system and particulates to the 15 degrees N region.
In soil moisture terms the region is ustic, which is possibly a necessary condition for bee-eater nests. The clastic material requires an ustic environment.
The River Niger can be seen as a loess river; in some senses a mirror-image of a major loess river like the Danube; but where a restricted range of particle inputs leads to a restricted range of loess deposit outputs. Nevertheless loess river considerations can be applied.
The Niger delivers second-order loess and an important loessic admixture to the landscape. Enough loess for selective nesters like the Carmine Bee-Eaters to build their nest tunnels in it.
It seems likely that climate change will cause a change in bee-eater distribution; it seems unlikely that they will abandon their nesting regions, the living and wintering zones may shift.