Demography and conservation of the White-tailed Tropicbird Phaethon lepturus on Aride Island, Western Indian Ocean
Résumé
The White-tailed Tropicbird Phaethon lepturus breeding population of Aride Island, Seychelles, has experienced a strong decline in the recent past. To predict the future trends of the White-tailed Tropicbird population on Aride Island and understand the urgency of applying management procedures, we developed a population matrix model. We estimated White-tailed Tropicbird adult survival rate over a 12-year period and investigated whether oceanographic conditions (El Niño Southern Oscillation, ENSO, and inter-annual climate variability in the Indian Ocean, Indian Ocean Dipole, IOD) or local factors ( Pisonia grandis fruiting events) potentially affect adult survival. Annual adult survival could not be linked to inter-annual variability in oceanographic conditions, but may be more influenced by Pisonia fruiting events, which, overall, accounts for 23.2% of the adult mortality. The growth rate of the population, primarily influenced by annual adult survival, was estimated to be 0.946, which indicates an annual population decline of 5.4%. At the current rate, the probability of extinction of this population would be 99% in 170 years. Management scenarios studied through Monte Carlo simulations, assuming small increments in adult survival and/or breeding success, dramatically reduce the risk of extinction of White-tailed Tropicbirds. Habitat management, in order to maintain an open canopy and little understorey vegetation, appears to be crucial for the conservation of White-tailed Tropicbirds on Aride Island, as has already been shown for other ground-nesting tropical seabirds nesting on forested islands.