Quantitative approach to the conservation of a tropical seabird population in the western Indian Ocean

The roseate tern (Sterna dougalli) is an oceanic seabird species showing mainly a tropical distribution, with a relatively fragile status worldwide. It was still recently considered as a "near-threatened" (IUCN red list) due to the strong decline in population trends over the last decades. For instance, the annual breeding population found on Aride Island, western Indian Ocean, has fluctuated between a high of 4,000 in the 1970's to a low of 60-1200 pairs from 2000 onwards. As a result, an intensive monitoring program was conducted on Aride between 1998 and 2006 in order to understand how environmental factors may affects this breeding population. This included the estimation of annual productivity (no of chicks fledged per pair), demographic parameters such as survival rate and recruitment (age-specific breeding probabilities), and their affecting co-factors (e.g. food availability, tick parasitism,...). We suggest that these three parameters (productivity, survival, recruitment) constitute the necessary basis to model the life-cycle of this population, and, ultimately, to provide local managers with conservations measures.