Breeding habitat and conservation priorities in Pterodroma baraui, an endangered gadfly petrel of the Mascarene archipelago

The endemic Barau's petrel (Pterodroma baraui) is restricted to the island of La Reunion in the Mascarene archipelago where it breeds on the upper slopes of the highest mountains in areas that are virtually inaccessible to humans. Although the species is considered to be critically endangered, little is known about its biology and the actual threats for Barau's petrel on its breeding grounds have never been investigated. In this paper we report data that were collected during the first ever visit of a Barau's petrel colony. The species breeds underground in upland elfin forests between 2400 and 2700 m above sea level. A thick, undisturbed, humus layer appears to be a prerequisite to burrow establishment, which implies that the species may be especially susceptible to trampling by humans or other large vertebrates. We found evidence of past exploitation of Barau's petrel by humans. In addition, the colony is inhabited by three, possibly four, species of introduced commensals, including Rattus sp., which imposes predation on eggs and chicks and may affect the breeding success. We stress the need to establish control campaigns to eradicate potential predators from the nesting colonies and long-term monitoring projects for the Barau's petrel before it undergoes irreversible population decline.