Migration, wintering distribution and habitat use of an endangered tropical seabird, Barau's petrel Pterodroma baraui

Gadfly petrels are strictly oceanic seabirds that range very far from their breeding grounds. Foraging movements outside the breeding season are poorly described. We used global location sensing (GLS) to describe the migration pathways and wintering habitats of Barau’s petrels Pterodroma baraui, an endemic, endangered seabird of Réunion Island (western Indian Ocean). In 2 consecutive years, petrels migrated far eastward, up to 5000 km from their breeding colony, to the central and eastern Indian Ocean. Migration pathways, timing, and wintering areas varied little among individuals, and non-breeding areas were remarkably consistent between years. There was no sexual variation in migration patterns. Barau’s petrels did not occur in the most productive areas of the Indian Ocean (Arabian Gulf and Somalia upwelling region) but instead foraged over warm oligotrophic and mesotrophic waters. Tracked birds consistently occurred in areas with relatively strong and consistent easterly winds, and avoided northern regions with weaker westerly winds. Our results indicate that Barau’s petrels use an expansive wintering area between the western South Equatorial Current and the eastern Equatorial Counter Current, characterised by warm sea surface temperatures (SST) and low productivity. However, wind regimes in the Indian Ocean are strongly influenced by the Asian Monsoon; in this particular area, wind and currents may create a frontal system where prey are aggregated, increasing their accessibility for Barau’s petrels. These results provide important baseline information for conservation, and are useful for the selection of potential marine reserves and the evaluation of effects of pollution or climate change on this highly threatened species.