War on feral cats triggers even worse disaster for Antarctic island

PUBLISHED : Wednesday, 10 January, 2007, 12:00am
UPDATED : Wednesday, 10 January, 2007, 12:00am

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.

The rabbits' relentless nibbling of tussock grass has led to soil erosion and the collapse of entire cliff-tops into the sea, destroying sea bird nests.

'Rabbits are destroying Macquarie Island's fragile vegetation, causing erosion and exposure, which threatens its seabirds,' warns a report released this week by the conservation group Birds Australia.

Jenny Scott, from the University of Tasmania's school of geography, has condemned the state of the island as 'an international disgrace'. The rabbit plague and extensive erosion had shocked the small number of eco-tourists who brave the 1,500km journey to the island from Hobart, she said.

Environmentalists are calling for urgent action to eradicate the rabbits and rats, which prey on seabird chicks and are threatening to wipe out six species of petrel, as well as rare species of albatross.

An aerial baiting programme has been proposed for the coming winter, when the birds will be at sea.

But wrangling over funding for the A$15 million (HK$91.2 million) eradication scheme has caused critical delays.

While Macquarie comes under the jurisdiction of Tasmania's state government, it is also a federal responsibility because it is a World Heritage site.

'The last supply boat of this season leaves Hobart in early April, so the two sides need to come to a cost-sharing arrangement and get their people and equipment on that boat,' said Julie Kirkwood of environmental group WWF.