Population Size and Breeding Phenology of Red-Billed Tropicbirds (Phaethon aethereus) on Iles de la Madeleine, Senegal

Abstract

The breeding phenology and nest site distribution of Red-billed Tropicbirds (Phaethon aethereus) was monitored from 6 June 2014 to 18 May 2016 on Parc National des Iles de la Madeleine, Senegal. During this period, this study site was visited every 15 days to record active nests and their contents (eggs or chicks). We found up to 76 nest sites but only 49 were active in 2014-2015 and 45 in 2015-2016. Red-billed Tropicbirds bred throughout the year but numbers of active nests peaked from October to January, which may be related to the seasonality of ocean upwelling. Nests were aggregated in four areas and their distribution and occupancy may be related to the direction of the wind during the seasonal peak of reproduction from October to May. The breeding success was generally high (62.9% in 2014-2015 and 47.3% in 2015-2016) compared to other colonies breeding in less productive waters. Given the singularity and small size of this population, monitoring, management and strict protection is clearly needed to guarantee its viability.