Eight seabird species (two of them endemic) of four families breed on Christmas Island. Between them they utilise at least 11 distinct breeding niches. They nest at different seasons and their species-specific breeding cycles differ in several basic ways. The object of this contribution is to analyse these factors, with particular reference to the families Sulidae and Fregatidae. Of the three sulids (Sula abbotti, S, sula and S.leucogaster) the endemic s'. abbotti is particularly important because of its rarity and the fact that so little has hitherto been discovered about its numbers, distribution on Christmas Island and breeding biology. Attention is particularly appropriate in view of the probable future destruction of its habitat. The extremely slow growth and consequent alternate year breeding of S. abbotti, together with its one-egg clutch, would impose severe restraints on the recuperative power of the population (now around 2,000 pairs).

Of the two frigate (fregata andrewi and F. minor) the status of the former is of considerable interest; its biology and prospects will be discussed. The emphasis throughout this contribution will be on the breeding biology of the species concerned, particularly in relation to conservation prospects.