In October and November 1991, more than 14,500 Cape Cormorants (Phalacrocorax capensis) in adult plumage died at eight islands off western South Africa. The overall observed mortality was 8% of the breeding population at these islands. At Dassen Island, where the highest mortality occurred, it was 16% of the breeding population. Mortality resulted from avian cholera (Pasteurella multocida), which also killed smaller numbers of African Penguins (Spheniscus demersus), Kelp Gulls (Larus dominicanus), Sacred Ibis (Threskiornis aethiopicus) and probably other waterbirds.