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

A R Martin,M G Richardson

doi:10.1017/s003060531700028x

Abstract

AbstractThe Subantarctic island of South Georgia lost most of its birds to predation by rodents introduced by people over 2 centuries. In 2011 a UK charity began to clear brown ratsRattus norvegicusand house miceMus musculusfrom the 170 km long, 3,500 km2island 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 128 km2Phase 1 trial operation. Work in 2013 (Phase 2) and early 2015 (Phase 3) covered the remaining 940 km2occupied by rodents. By July 2017, 28 months after baiting was concluded, there was no sign of surviving rodents, other than one apparently newly introduced by ship in October 2014. A survey using detection dogs and passive devices will search the Phase 2 and Phase 3 land for rodents in early 2018. Seven (of 30) species of breeding birds suffered losses from poisoning, but all populations appear to have recovered within 5 years. The endemic South Georgia pipitAnthus antarcticuswas 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.

Highlights

Invasive alien species have long been recognized as a major cause of extinctions on islands, with rodents being among the most destructive animals in this regard (Jones et al, )
The only methodology offering any chance of success on an island with the land area and topography of South Georgia was aerial spreading of bait that contained a rodenticide with a proven capacity to eradicate rodents
Phase 3 Fresh signs of live rats stopped within a week of baiting

Summary

Introduction

Invasive alien species have long been recognized as a major cause of extinctions on islands, with rodents being among the most destructive animals in this regard (Jones et al, ). A breakthrough was made in , when the , ha Campbell Island was successfully cleared of brown rats (McClelland & Tyree, ) Was this eradication larger than any of its predecessors, but the island was, like South Georgia, remote and in the Subantarctic. The only methodology offering any chance of success on an island with the land area and topography of South Georgia was aerial (helicopter) spreading of bait that contained a rodenticide with a proven capacity to eradicate rodents. This technique had been successful on Campbell Island and was the standard methodology for islands unsuitable for ground baiting methods (Broome et al, ). Rodents occupied c. % of the land area of the main island of South Georgia, and all of the terrain favoured by native wildlife

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Discussion