After seven long and challenging years, the world’s largest and most ambitious rodent eradication has been declared an international success.
(Main photo credit: Tony Martin)
On 8th May 2018 the UK Overseas Territory of South Georgia (approximately 1300 km east of the Falkland Islands, in the southern Atlantic Ocean) was officially declared free of rodents for the first time since humans arrived on the island over 200 years ago.
At over 1087km2 in size, the area that was cleared of invasive rodents is more than eight times larger than Macquarie Island, previously the largest island to be cleared of rodents.
Two centuries of devastation
South Georgia had been an island rich with marine and native birdlife until the late 18th century. When the island was discovered by Captain Cook in 1775, his reports of the numerous whales and seals reached the ears of British and American industrialists and for 200 years, South Georgia was an active whaling station. As humans arrived by boat, they also brought with them two highly destructive pests: Rattus norvegicus and Mus musculus.
Norway rats devastated the island’s seabird populations. In the absence of natural predators, their presence grew and threatened the existence of two of the islands endemic species, found nowhere else on earth: the South Georgia pipit and South Georgia pintail. Rodents overran the island, forcing the birds to move to smaller offshore, rodent-free islands.
A custom solution
The ambitious Habitat Restoration Project began in 2008, undertaken by the South Georgia Heritage Trust and its USA counterpart the Friends of South Georgia Island. The AUD$18 million project aimed to reverse two centuries of human-induced damage to the island’s wildlife.
The project began with South Georgia Heritage Trust studying the biology and species present on the island in order to determine the best way to target rodents without threatening native wildlife. As is normal with large-scale eradication programs, aerial baiting was the agreed plan of action. The challenge was finding a bait that was durable enough to survive aerial (helicopter) baiting while also being palatable to the rodents, with minimal risk of primary or secondary poisoning to non-target species.
The project team worked with Bell Laboratories to develop a custom bait. The result was the creation of a large, green pellet based on the Australian Ditrac formulation that was tough enough to survive aerial baiting. It was too large for most of the bird species to easily consume yet small enough for rodents to eat. The Brodifacoum Conservation Pellets also featured Bell Laboratories’ Lumitrack, a special additive that causes rodent droppings to brightly glow under UV or black light. This helped the project team trace the bait distribution and track rodent activity.
Five-year baiting schedule
Due to the topography and distribution of wildlife, the project team was able to spread out the aerial bait drops over a five-year period rather than having to attempt a simultaneous treatment. The pilot phase of baiting began in 2011, followed by a second phase in 2013 and a third phase in 2015. Interestingly, the first phase of baiting alone made this project the largest island rodent eradication operation ever undertaken in the world.
The final third phase, which began in January 2015, saw three helicopters and just over 100 tons of bait being shipped to the island. Helicopter pilots flew almost 450 hours in challenging weather conditions to successfully make the very last drop. Over the three seasons, more than 800 bait loads had been dropped, requiring nearly 1,000 helicopter flying hours.
Searching for signs
After the final baiting phase, it was evident that some bird species had quickly begun to recover in number, but a comprehensive survey was needed before the island could officially be declared free of rodents.
For two years, the expedition team – dubbed ‘Team Rat’ – deployed and monitored over 4,600 inert devices, including chewsticks and tracking tunnels across the island, searching for signs of surviving rats. Three highly trained ‘sniffer’ dogs and their two skilled handlers spent many months walking the island, covering a total of 2420km. This distance, equivalent of a trip from Sydney to Cairns, is all the more impressive given the rugged and challenging terrain of South Georgia. Together, the handlers climbed the equivalent ascent of Mount Everest eight times over.
On 8th May 2018, Professor Mike Richardson, chairman of the Habitat Restoration Project Steering Committee announced that the rodents had been successfully eradicated from the island. “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.
“The popular TV series Blue Planet highlighted our shared environmental challenges and raised awareness of South Georgia’s importance to seabirds and nature more widely. We hope the results from this project will continue to inspire others to help protect our natural world.”
Lord Gardiner, Parliamentary under-secretary of the UK’s Department for Environment, Food & Rural Affairs, added, “The last ten years has seen a step-change in how the UK responds to invasive non-native species and 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.”