Rodent eradication scaled up: clearing rats and mice from South Georgia

The Subantarctic island of South Georgia lost most of its birds to predation by rodents introduced by people over  centuries. In  a UK charity began to clear brown rats Rattus norvegicus and house miceMus musculus from the  km long, , km island using helicopters to spread bait containing Brodifacoum as the active ingredient. South Georgia’s larger glaciers were barriers to rodent movement, resulting in numerous independent sub-island populations. The eradication could therefore be spread over multiple seasons, giving time to evaluate results before recommencing, and also reducing the impact of non-target mortality across the island as a whole. Eradication success was achieved in the  km Phase  trial operation. Work in  (Phase ) and early  (Phase ) covered the remaining  km occupied by rodents. By July ,  months after baiting was concluded, there was no sign of surviving rodents, other than one apparently newly introduced by ship in October . A survey using detection dogs and passive devices will search the Phase  and Phase  land for rodents in early . Seven (of ) species of breeding birds suffered losses from poisoning, but all populations appear to have recovered within  years. The endemic South Georgia pipit Anthus antarcticus was the first bird to breed in newly rat-free areas, but there were also signs that cavity-nesting seabirds were exploring scree habitat denied them for generations. Enhanced biosecurity measures on South Georgia are needed urgently to prevent rodents being reintroduced.