Ecologists become hunters to rid island of every rat

South Georgia is home to about 30 million birds, which scientists want to protect through an ambitious rat-eradication plan. Photo / AP

The world's biggest rat-hunt is being mounted to rid a South Atlantic island of the rodents eating their way through millions of endangered seabirds.

The first phase of the eradication programme will start next February on South Georgia in the hope of returning the island to its previous state as a globally important breeding site for seabirds. Over the centuries, the rats arrived on South Georgia off whaling ships and sealers. Since then, their population has grown to several million, feeding on the eggs and live chicks of the ground-nesting birds that breed on the island, nearly 1500km east of the Falklands.

Invasive rodents have been successfully removed from more than 300 islands worldwide but the South Georgia operation is by far the biggest and most ambitious, involving spreading poisoned bait over every square metre of ice-free land on the 170km-long island. But the hunters have to make sure every rat is killed. They reproduce so swiftly that leaving one pair alive means 15,500 more within a year.

"It's easily the largest rat-eradication effort in the world, at least seven times bigger than anything anyone has tackled before," said Tony Martin, professor of animal conservation at the University of Dundee who is in charge of the multi-million dollar project.

South Georgia is home to about 30 million birds. Some 31 species breed on the island, including grey-headed albatrosses, northern giant petrels, white-chinned petrels, Antarctic prions, half of the world's entire population of macaroni penguins and the South Georgia blue-eyed shag. A further 50 species are known to visit the island.

The South Georgia pipit is close to extinction. Ground-nesting birds have no natural mammalian predators and so their chicks and eggs are defenceless against the brown rat.

The only barriers to the rat on South Georgia are the ice tongues of the glaciers which protrude out to sea and isolate some bird colonies from the rats. But these glaciers are retreating rapidly inland and as soon as they shrink away from a beach rats are able to find new bird colonies to attack, Martin said.

Pellets of a cereal bait loaded with an anti-coagulant poison will be spread across all rat-infested parts of the island by helicopter. A key advantage of the bait is that it can be detected by rats up to 300m away because they are so attracted by its smell.

The poison, which quickly degrades and does not dissolve in water, gets into the liver and causes internal bleeding. It does not kill immediately and makes the rats sensitive to light so it is hoped they will retreat to their burrows to die rather than dying out in the open so that their poisoned corpses are eaten by the seabirds.

"I'm not going to pretend that it's a nice way to die but it's the way rats are killed worldwide and if you leave them the seabird chicks will suffer an even nastier death of being eaten alive," Professor Martin said.

The first phase of the project will begin in autumn next year when many migratory birds have left the island and the rats have stopped breeding. After a year, the scientists hope to have completed the eradication.

Once the rats have gone, it is hoped that seabird numbers will increase to their previous levels. "This is perhaps the most exciting project of my career because the legacy of this will last for millennia," Martin added.

- INDEPENDENT