Summary.The birds seen on the Berlengas, the Desertas, Baixo Island, and the Salvages in June and July 1939 are listed and field notes are given on certain species.InPuffinis kuhlii borealisincubation was by both sexes. Where it is unmolested by man, as at Grande Salvage, this bird is partly diurnal in visiting the land; where molested, as on the Berlingas' and Desertas, it is nocturnal.InBulweria bulweriiincubation is by both sexes, probably in shifts of two or more days.At Grande Salvage there appears to be a division of the year into specific breeding seasons by which the maximum use is made of the ground–burrows by two if not three species of petrels. This probable breeding competition is discussed, and other examples suggested from the literature of petrels breeding on small tropical and sub–tropical isla