After more than 200 years, the British Overseas Territory of South Georgia is rodent-free. The focus of the world's largest rodent eradication project taking 10 years and costing £10 million (US$13.5 million), the almost uninhabited South Atlantic island has officially been declared free of all rats and mice by Scottish-based charity the South Georgia Heritage Trust (SGHT).
Invasive species are among the biggest environmental headaches. The deliberate or accidental introduction of foreign flora and fauna, no matter how seemingly innocuous, can have devastating results. The effects can range from one species displacing another to whole regions being ravaged by out-of-control invaders that strip the land bare of vegetation.
One particularly successful group of invaders are rodents – especially rats and mice. These omnivorous pests are excellently adapted to live alongside humans and they have followed our species wherever we have gone, with the exception (for now) of space.
A tragic example of this migration is South Georgia. Discovered and named by Captain James Cook in 1775 on one of his epic voyages of exploration, it's regarded as one of the world's last great wilderness areas. It's the home of 98 percent of the world's Antarctic fur seals and half the world's elephant seals. In addition, it's host to colonies of four species of penguins – including 450,000 breeding pairs of King penguins – albatrosses, prions, skua, terns, sheathbills, petrels, and the endemic South Georgia Pipit and South Georgia Pintail.
Unfortunately, it was, until now, also home to a thriving horde of rats and mice, which were brought ashore by sealers in the 18th century and by the whalers who set up a station in the 19th that remained operational until 1966. These rodents had a terrible impact on the local birds, which nest on bare ground or in burrows and had never had to face predators before. Within decades, the rodents had fed on so many eggs and chicks that many bird species were confined to tiny offshore islands that the rats couldn't reach.
To combat this, the SGHT and its US-based counterpart, the Friends of South Georgia Island (FOSGI), instituted the Habitat Restoration Project in 2008. By that time, the whaling stations were abandoned and salvaged and the only temporary inhabitants were about 20 scientists and occasional visitors from the Royal Navy's local guard ship, so eradication of the rodents finally became feasible.
The task of the project was to cover 1,087 km² (419 mi²) – an area eight times larger than any previous rodent eradication effort that included some of the harshest, most mountainous terrain imaginable. A pilot phase of baiting began in 2011, followed by a second phase in 2013/14 and a third phase in 2015/16. During this time, over 300 tonnes of poisoned bait was distributed by helicopter and by hand.
This was followed two years later when an extensive six-month survey of the island was made using chewsticks, survey tunnels, and three detector dogs with two handlers who covered a walking distance of 2,420 km (1,500 mi) and 1,608 km (1,000 mi), respectively.
According to the Trust, there are no signs of any rodents going back two years after the baiting work and the native bird population is already recovering in some areas.
"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," says Professor Mike Richardson, Chairman of the SGHT Habitat Restoration Project Steering Committee. "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."
SGHT will now work to help the Government of South Georgia & the South Sandwich Islands to prevent the return of the rodents to South Georgia.
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