Re-colonisation and successful breeding of Masked Boobies Sula dactylatra on mainland St Helena, South Atlantic, in the presence of Feral Cats Felis catus

Masked Boobies Sula dactylatra were apparently extremely abundant on St Helena in the early sixteenth century, when the island was discovered. It is probable that the breeding population was severely depleted by man and introduced mammalian predators following human settlement of the island in 1659. The species had certainly become very scarce by the nineteenth and twentieth centuries, restricted to a few small offshore stacks that remained predator-free. The first fully documented breeding, on Shore Island a small predator-free stack, was as recent as 1988. Since that time, the population has increased substantially, and here we report the first instance of breeding on the St Helena mainland, despite the presence of Feral Cats Felis catus, Brown Rats Rattus norvegicus and Black Rats R. rattus. In July 2009, along 4 km of coastline in the southwest of the island, one pair was discovered with a large downy chick, four pairs were confirmed to be incubating eggs, and a further 25 pairs were apparently incubating eggs. Subsequent monitoring of 28 breeding attempts up to July 2010 revealed moderate levels of breeding success (0.461 young fledged per attempt), which were substantially higher than those of Masked Boobies that have re-colonised Ascension Island in recent years following cat eradication. The ability of Masked Boobies to nest successfully, on occasion, on islands where cats and rats are present, highlights their potential resilience to these introduced mammalian predators, and the circumstances and long-term viability of successful co-existence with such non-native predators warrant further investigation.