Life-history characteristics buffer seabird populations from variations in their food supply on time scales of several years or less. There are longer-term changes in food availability caused by decadal-scale regimes of prey populations and century-scale trends in the utilisation of forage resources by man and other predators. Responses during the 20th century of three southern African seabirds to such low-frequency variability are described. The three seabirds, African Penguin Spheniscus demersus, Cape Gannet Morus capensis and Cape Cormorant Phalacrocorax capensis are all endemic to the region and subsist to a large extent on sardine Sardinops sagax and anchovy Engraulis capensis. Sardine collapsed off South Africa in the 1960s and off Namibia in the 1970s, with anchovies being the dominant species off South Africa. Collapse of the sardine was followed by massive decreases in penguin colonies between Lüderitz and Table Bay, but increases in colonies north of Lüderitz and southeast of Table Bay. There were large decreases in Namibian gannet colonies, whereas those in South Africa increased. Populations of Cape Cormorants increased in both countries. In the 1980s, there was a resurgence of sardine off South Africa, where anchovy started to decrease with fluctuations. There was a large decrease in penguins at Dyer Island, southeast of Table Bay, whereas colonies between Lüderitz and Table Bay stabilised. Three new penguin colonies were established in the vicinity of Table Bay and grew rapidly. South African colonies of Cape Gannets remained stable or continued to increase, but there was poor breeding by Cape Cormorants when anchovy was scarce. The overall populations of penguins and gannets were buffered to an extent against decadal-scale changes in the food base by the ability of first-time breeders to move to colonies where food was plentiful at the time. Additionally, both species were able to switch their diet between anchovy and sardine. Cape Cormorants have not utilised sardine as effectively as anchovy, but are able to move to areas where anchovy is abundant and have potential to increase more rapidly than penguins and gannets.