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ABSTR• ½T.--Numerous studies of predatory birds worldwide report dietary proportions based on analyses of large numbers of pellets or prey remains. Such analyses are often severely biased, hence strictly unquantifiable, because some prey remains are more conspicuous or persistent than others. We investigated this bias for the bird-and micromammal-eating African Marsh Harrier (Circus ranivorus), using an essentially independent measure of diet, observed prey deliveries to the nest. Comparisons of the frequency of occurrence showed that bird prey, particularly large wetland species, were over-represented almost threefold among remains. Micromammals were under-represented about 1.5-fold, while fish, frogs and eggs were marginally over-represented. Analyses using pellets were also biased but in the opposite direction to that of remains. We show that by combining pellets and prey remains (collected with equal effort), accurate estimates of overall diet can be achieved. This was verified using month by month comparisons of micromammals, in which proportions derived from pellets and remains never differed by more than

10% from those established from direct observations.