Audubon's Shearwaters Puffinus Iherminieri on Réunion Island, Indian Ocean: behaviour, census, distribution, biometrics and breeding biology

Abstract

Audubon's Shearwater Puffinus Iherminieri is a little known species of petrel. The recent descriptions of a possibly new species (P. atrodorsalis) and a new subspecies (P. l. colstoni) have suggested that the population breeding on Réunion Island, P. l. bailloni, may represent a key taxon for understanding the phylogeography of this group in the Indian Ocean. We provide the first detailed information on distribution, abundance, habitat characteristics and breeding biology of the species on Réunion, and assess relationships between the Indian Ocean taxa based on biometrics, coloration characters and patterns of breeding phenology. We also studied the behaviour of the birds on Réunion, paying particular attention to vocalizations. Analysing the parameters that affect calling rate, such as moonlight, season and time, we show that calling activity can be used to estimate colony size. Using this method, we sampled more than half of Réunion Island habitats suitable for Audubon's Shearwater, and estimate that the breeding population there is between 3000 and 5000 pairs in at least 235 colonies. Compared to other Indian Ocean populations (n= 136 specimens), the analysis of biometrics and coloration characters suggests that three main populations exist (Comoro, Réunion and Seychelles), with birds of Maldives and Amirantes being biometrically inseparable from those of Seychelles, and birds from Aldabra being intermediate between Seychelles and Réunion. The proposed new species, atrodorsalis, also falls in the overlap between Seychelles and Réunion birds, which argues against a full species taxonomic status.