Ships of sealers and whalers arriving on South Georgia brought with them rats and mice that spread over much of the island, eating eggs and chicks of the native birds.

To counter the problem of invasive rats, the South Georgia Heritage Trust launched a $13.5 million rodent eradication operation in 2011, using helicopters to drop poisoned bait in every part of the island that could be infested with rodents.

In the final phase of monitoring that concluded in April this year — a six-month survey that included three trained sniffer dogs — the SGHT team found no signs of rats or mice.

The remote island of South Georgia in the southern Atlantic Ocean has finally been declared free of invasive rats and mice in the world’s largest-ever rodent eradication effort.

A monitoring survey last month, which included three trained sniffer dogs, found no trace of any rats or mice on the island, making the island officially “rodent-free” for the first time in over 200 years, the U.K.-based charity South Georgia Heritage Trust (SGHT) announced at a press conference in London on May 8.

“South Georgia Heritage Trust is delighted to declare that its Habitat Restoration Project is complete and that invasive rodents have been successfully eradicated from the island,” Mike Richardson, chairman of the SGHT Habitat Restoration Project Steering Committee, said in a press release. “It has been a privilege to work on this conservation project, the largest of its kind anywhere in the world, and I am immensely proud of what the small charity has achieved — it has been a huge team effort.”

Covered in glaciers, ice caps and snowfields, South Georgia is an important breeding site for Antarctic fur seals (Arctocephalus gazella) and southern elephant seals (Mirounga leonina).

It is also home to the Macaroni penguin (Eudyptes chrysolophus), Gentoo penguin (Pygoscelis papua), chinstrap penguin (Pygoscelis antarcticus), and around 450,000 breeding pairs of the King penguin (Aptenodytes patagonicus). Moreover, the island is a critical nesting site for millions of birds, including two species found only on the island: the South Georgia pipit (Anthus antarcticus) and South Georgia pintail (Anas georgica georgica).

British explorer Captain James Cook first discovered the sub-Antarctic island of South Georgia in 1775. Soon, sealers and whalers arrived on the island, a U.K. overseas territory, to exploit the bounty of seals and whales for skin and oil. Thousands of people aside, the ships also brought rats and mice that spread over much of the island, eating eggs and chicks of the native birds, especially the endemic ones.

To counter the problem of invasive rats, the SGHT launched a £10 million ($13.5 million) rodent eradication operation in 2011, using helicopters to drop poisoned bait across every part of the island that could be infested with rodents.

Over three phases of baiting, the SGHT covered an area of 1,087 square kilometers (420 square miles), which the team says is “more than eight times larger than any other rodent eradication area ever tackled anywhere in the world.” The last bait was dropped in 2016, but the team wanted to comprehensively survey the island before officially declaring it rodent-free.

In the final phase of monitoring, which concluded in April this year, three detection dogs — Wai, Will and Ahu — especially trained to detect rodents, joined a 16-member expedition team dubbed “Team Rat” to survey the island for signs of rats and mice. After six months of intensive searching, which included the three terriers covering an impressive 2,420 kilometers (1,500 miles), the expedition team found no trace of rodents on the island.

“Thanks to the outstanding work of the passionate and committed members of Team Rat and the Board of Trustees, the birds of South Georgia are free from the threat of rodents,” Richardson said.

Lord Gardiner, the U.K. parliamentary undersecretary at the Department for Environment, Food and Rural Affairs, added: “The rodent eradication work completed by the South Georgia Heritage Trust is undoubtedly among the most remarkable of recent island conservation efforts. This successful project gives confidence and offers hope for invasive alien species management around the globe.”

However, climate change could pose a challenge to the management of invasive species in the future.

The glaciers on South Georgia have subdivided the island into discrete areas of habitats suitable for rats, a 2010 study noted, with the glaciers acting as barriers for the rodents and preventing them from colonizing the entire island. But the retreat of glaciers on the island due to climate change could make tackling future invasions difficult.