In the 18th century, sealing and whaling ships accidentally introduced rodents to South Georgia, an island in the southern Atlantic Ocean. The tiny creatures multiplied and soon proved a menace to the bird populations, eating their eggs and chicks.
Now, after the world’s largest rodent extermination effort, scientists have finally declared the island free of rats and mice, Fiona Harvey reports for The Guardian.
The announcement comes after years of work ridding the island of pests. In 2011, the South Georgia Heritage Trust, a Scotland-based charity, began dropping more than 300 tons of poisoned bait across 269,000 acres of the island where rodents were thriving, New Scientist reports.
Costing some $13.5 million, the poisoned bait drop continued for four years. The charity made the official announcement of the island’s rodent-free status last Monday.
“It’s really exciting to have it official that South Georgia is rodent-free,” Clare Stringer, head of international species recovery at the Royal Society for the Protection of Birds and who was not involved in the project, tells Matt Warren for Science. “It’s what we were all hoping for.”
As BBC News’ Jonathan Amos reports, total extermination was possible thanks to the island’s glaciers, which prevented the rats from crossing icefields and divided the territory into “convenient killing zones.”
After the bait drops ended in 2015, the group began the long wait to ensure the rodents wouldn’t return. Even a few critters could lead to repopulation thanks to their fast reproduction rates. And the group didn’t want to claim success too quickly, Warren reports.
This past winter, a survey team, dubbed “Team Rat”, canvassed more than 1,500 sites in search of rodents. The group deployed thousands of peanut butter-coated chew sticks, camera traps and tracking tunnels, according to New Scientist. Three sniffer dogs also walked hundreds of miles to check for rodent activity.
No signs were found, marking the first time in roughly 250 years that the island has been free of mice and rats.
Restoration project director Dickie Hall tells Amos that he’s confident in the team’s findings. "Dogs have an incredible sense of smell," says Hall. "They can detect rodent scent from several meters, or even tens of meters if conditions are right.”
More than 30 different species of birds live on the island, including penguins and albatross. Most of these creatures nest on the ground or in burrows since there are no trees—but this leaves their nests vulnerable to rodent predators, reports Harvey.
According to Amos, two of the hardest-hit species on the island were the South Georgia pipit and the South Georgia Pintail. Neither of these birds live anywhere else on the planet.
But these birds already seem to be bouncing back, Amos reports, and the government of South Georgia and the South Sandwich Islands has high hopes for the island's wildlife. Another eradication plan, this time targeting non-native plant species, will begin in 2020, according to a press release.
“It is hoped that in the wake of the various eradication efforts, South Georgia’s iconic seabird populations will flourish, the endemic South Georgia pipit will be brought back from the brink of extinction and native vegetation communities will flourish,” according to the release.
Additional work will be required to monitor the project’s impact. But scientists are optimistic it could serve as a model for other areas around world that need to eliminate invasive species. As Warren writes, at least one other country is working on a similar project: New Zealand aims to eradicate all major mammalian predators by 2050.