SUMMARYThree colonies of Brown Noddies on stacks north of Georgetown, Ascension Island, were visited 24 times between November 1957 and April 1959. During this period there were two main breeding seasons, about a year apart, but in each season there was both an early and a late peak of laying: rollers washing over the stacks may have been partly responsible for this. The moult cycle of the Brown Noddies was probably an annual one, but on Ascension there appeared to be no tendency for moult to stop during breeding: this situation contrasts with that found in other populations of the species. A small number of food samples were obtained, which showed that the diet of the noddies included a variety of fish and some squid. Young Brown Noddies in many parts of the world show a polymorphism in down colour which is still very poorly known; on Ascension most chicks are almost white, about a sixth more or less dark. Diagrams showing the growth of young noddies are given. The age and state of development at which young Brown and Black Noddies and Fairy Terns first fly are considered, and the reasons for the differences between different species and populations are briefly discussed.