Norway rats ( Rattus norvegicus) on Frégate Island, Seychelles: the invasion; subsequent eradication attempts and implications for the island's fauna

Abstract

In July 1995 Frégate Island in the Seychelles was colonised by Norway rats ( Rattus norvegicus). Prior to this date, Frégate was the largest rat-free island in the inner, granitic, group of the Seychelles archipelago. An eradication attempt was made in June 1996 to protect the unique fauna of the island, including the critically endangered Seychelles magpie-robin ( Copsychus sechellarum). This was the first time an attempt had been made to eradicate a newly arrived and rapidly expanding rat population. The attempt was abandoned after several Seychelles magpie-robins died through secondary rodenticide poisoning. Possible biological consequences of continued rat presence on Frégate Island are discussed and recommendations made that are relevant to other invasions of islands by rats. This is the first time that a rat invasion of a biologically important conservation island has been documented in any depth.