Population fluctuations and their causes in the African Fish Eagle, (Haliaeetus vocifer (Daudin)) at Lake Naivasha, Kenya.

The population of (Haliaeetus vocifer (Daudin)) at Lake Naivasha, Kenya, was censused over a 13-year period (1987-99). During this time it declined by over half, to alow of 70 birds, by 1996. Breeding effectively ceased, with no courtship or nesting observed for most of the 1990s. The reason seemed to be a food shortage, which provided enough to stay alive but not enough to breed. Declines in the main prey items - fish species and red knobbed coot (Fulica cristata), occurred during the early 1990s and feeding conditions were worsened by a combination of increased turbidity in the lake, floating mats of exotic vegetation and the loss of shallow lagoons behind fringing Cyperus papyrus. This explanation was confirmed when heavy rains, following the strong ENSO event in 1997-98, caused a rapid lake level rise of 3 m vertically, flooding new lagoons behind formerly stranded C. papyrus. Breeding re-commenced, leading to 17-24 fledged juveniles in a population exceeding 100, by 1999. This population of H. vocifer is a valuable index of both the health of the lake and of its littoral ecotone. [ABSTRACT FROM AUTHOR]