THE MADEIRAN STORM PETRELOCEANODROMA CASTRO

SUMMARY The Medeiran Storm Petrel breeds annually on Boastwain Bird Island and probably has a 12-month sexual cycle. The birds first arrive in July and most of the eggs are laid in November. During 1958–59 when the British Ornithologists' Union Centenary Expedition was on Ascension Island, the population of petrels was calculated to be 3,000 birds. There were signs of overcrowding in the colony, which reduced the breeding success. The behaviour of the colony suggested that there was a fertility gradient through the population. That this gradient might change in response to population fluctuation is discussed. A detailed description is given of the growth and development of normal and retarded chicks together with recordes of egg losses and injuries to adults and chicks.