SUMMARYAscension Island Frigate Birds (present population 8,000–10,000 breeding adults) were studied on Boatswain Bird Island between November 1957 and April 1959. Eggs were laid throughout the year, but a breeding season of eight to nine months (April to November or December) was apparent in 1958 and there was evidence of a similar season in the previous year. The birds tended to nest in groups, at densities varying from one or two to over 60 per area of 50 square metres; some nested at densities of two or three per square metre. Nesting success was highest among early breeders, out‐of‐season breeders and those breeding in low‐density groups, and was very much lower in the areas of dense nesting; greatest losses were among eggs and young chicks, and a nesting success of 15°‐20° is indicated for the population as a whole. Courtship, nesting and growth of the chicks ar