Abstract
the trophic ecology of the Bridled tern Onychoprion anaethetus is poorly understood despite its great abundance in tropical and subtropical regions. Important breeding colonies are located in the Caribbean, where significant human disturbances occur and where coverage by marine protected areas is still largely insufficient. Bridled tern populations are likely to experience considerable variation in trophic niche throughout their annual cycle, especially between the non-breeding and breeding phases as they change their feeding areas. In this study, we assessed the year-round variability of the Bridled tern isotopic niche (δ15N and δ13C) from two breeding areas in North Central Cuba, as a proxy of its trophic niche. Feathers, down and blood samples were taken from adults and chicks, representing four life cycle phases of this species (non-breeding, pre-laying, incubation and chick-rearing). Overall, Bridled terns occupied a narrow and relatively plastic isotopic niche, along the studied life cycle phases. the largest variability occurred between the non-breeding and the pre-laying phases, showing a marked reduction of the niche breadth. Patterns of niche variability differed among breeding areas only during the incubation phase. Considering that adult females of Bridled tern rely on few prey species during the pre-laying, this life cycle phase is a period of high vulnerability for the Cuban colonies.