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Previous observations on Pycroft’s petrel (Pterodroma pycrofti) are summarized and distribution of the species is discussed. There are no records north of New Zealand, nor any to the south of the breeding-grounds. The nesting habitat is described, especially with reference to the apparent preference of Pycroft’s petrel for pohutukawa (Metrosideros excelsa) forest. Eggs are laid during the last week of November and the first week of December, with a peak on 26 November. Incubation is commenced by the male. Repeated desertion is discussed, with shortage of food reserves as a possible cause. Incubating birds lose 3–4 gm. per day. The mean weight for the species is 159 gm. On the breeding grounds eighty-one per cent of the population are unemployed birds. The proportion of unemployed birds in other petrel populations is discussed. The activity of breeding birds is compared to that of unemployed birds. Unemployed birds are responsible for calls heard over the colony in the air, most breeding birds arriving inconspicuously. The unemployed population may exert a social stimulus on the breeding birds. In the Appendix, individual burrows are described. Frequent reference has been made to the literature on petrel behaviour and ecology, and work on some important aspects is reviewed.