Prey diversity and selectivity of the African fish eagle: data from a roost in northern Kenya

Abstract

A total of 1872 bones from a fish eagle roost at Lake Turkana, Kenya was identified and analysed to provide data on fish eagle prey and diet. The approach of this study complements field observation studies in that it provides a long‐term analysis and quantification of the diet, rather than short qualitative observations. The study found that, at least where fish is relatively abundant, fish eagles are both selective and opportunistic: selective in taking preferred fish in much greater proportions than natural availability, and also in avoiding unwanted fish regardless of abundance, but opportunistic in taking certain other species in proportion to their availability. They also show considerable selection in size and habitat preferences of prey. Non‐fish prey forms a considerable proportion of the diet, and probably represents both opportunistic hunting, possibly when conditions for fishing are poor, and killing of other predators robbing fish eagle nests.As well as describing and quantifying the fish eagle diet at Lake Turkana, data from this study suggest that further study is needed to quantify the impact of fish eagle predation on Clarias lazera, a rare, but valuable species to the Lake Turkana fishery. The study of bird roost prey remains also provides baseline data for studies of fossil microfaunal accumulations. Scatters of bones under fish eagle roosts are common in eastern Africa, and undoubtedly contribute to many of the fossil bone accumulations recovered. One of us (DM) has noted that the taxonomic and skeletal composition of the Koobi Fora roost bears a great resemblance to some of the clusters she is analysing from Olduvai Gorge. Further similar studies will provide additional data on bird roost accumulations.