War on feral cats triggers even worse disaster for Antarctic island

A plan to clear a remote Australian island of feral cats to save rare seabirds has unleashed an ecological domino effect that has dismayed conservationists.

Scientists have branded the environmental degradation of Macquarie Island, a sub-Antarctic territory at the bottom of the world, an international embarrassment.

Cats were introduced to the island by whalers in about 1820 and have had a devastating impact on its seabird colonies.

Until recently, nearly 2,500 cats were marauding the island, halfway between Tasmania and Antarctica, killing an estimated 60,000 seabirds a year. Specially trained dogs were used to hunt down the predators, with the last feral feline humanely destroyed in June 2000.

Seabird numbers began to increase, to the delight of conservationists. In 2004, the endangered grey petrel bred on the island for the first time since the 1960s, raising hopes that other rare species, such as the blue petrel, might also bounce back.

But in a chain of events that demonstrates the complexity of restoring nature's balance, the removal of the cats had an unforeseen consequence - an explosion in the number of rats and rabbits on the island.

The rabbit population on the 87,000-hectare island has increased from 10,000 in the mid-1980s to a staggering 100,000.