Abstract
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.
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Acknowledgments
We would like to acknowledge all the wardens, rangers and volunteers who helped collect data during the ringing-tropicbird program. James Cadbury financed the travelling of J.A.R. and D.M. to Aride Island. We thank J.D. Nichols and J. Hines for valuable advice on mark–recapture data analysis and an anonymous referee for valuable comments. T.C. and D.M. were funded by doctoral grants from Fundação para a Ciência e Tecnologia (SFRH/BD/16706/2004) and the Belgian Services Scientifiques, Techniques et Culturels (SSTC, Action II-Contract WI-36-D03), respectively. This research was conducted under permission of the Seychelles Bureau of Standards, Republic of Seychelles.
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Communicated by J. Fjeldså.
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Catry, T., Ramos, J.A., Monticelli, D. et al. Demography and conservation of the White-tailed Tropicbird Phaethon lepturus on Aride Island, Western Indian Ocean. J Ornithol 150, 661–669 (2009). https://doi.org/10.1007/s10336-009-0389-z
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DOI: https://doi.org/10.1007/s10336-009-0389-z