The habits, feeding and plumage variations of the Black-fronted Tern (Sterna albostriata) were studied during their April to August wintering period in the Bay of Plenty, from 1977 to 1981. Their migration to and from, and occurrence in, the North Island is discussed. The possibility of numbers visiting the Bay of Plenty being on the decline is raised. The study of the plumage variations led to the conclusion that two age-groups are present and readily recognisabIe during their entire stay in the Bay of Plenty and a third is recognisable for at least 3 months of the wintering period. The extent of time over which the autumn-winter moult of the adult takes place is discussed.