Strategy to remove cats backfires on tiny island

BANGKOK, Thailand — It seemed like a good idea at the time: Remove all the feral cats from a famous Australian island to save the native seabirds.

But the decision to eradicate the felines from Macquarie Island allowed the rabbit population to explode and, in turn, destroy much of its fragile vegetation that birds depend on for cover, researchers have reported.

Removing the cats from Macquarie "caused environmental devastation" that will cost authorities $16.2 million to remedy, Dana Bergstrom of the Australian Antarctic Division and her colleagues wrote in the British Ecological Society's Journal of Applied Ecology.

"Our study shows that between 2000 and 2007, there has been widespread ecosystem devastation and decades of conservation effort compromised," Bergstrom said in a statement.

Two attempts to reverse a man-made environmental catastrophe on a sub-Antarctic island have backfired, requiring the expensive rescue plan and providing a warning for scientists attempting to remove invasive species in other regions.

Macquarie Island is a 50-square-mile dot in the Southern Ocean about halfway between Australia and Antarctica.

It is a World Heritage Site because it is the only place where rocks from the Earth's mantle are being actively exposed above sea level.

Soon after the island was discovered in 1810, seafarers arrived to slaughter fur seals, elephant seals and penguins for their fur and blubber.

When the sailors docked, rats and mice abandoned the ships and took up residence, attacking food stores on land. To counter them, the sailors started bringing cats to the island about 1818.

As was tradition, sailors also introduced rabbits to the island about 60 years later to provide a food source for stranded seamen.

Cats and rabbits proliferated, with the rabbit population reaching about 130,000 in the 1970s.

The cats fed on both the rabbits and native birds, and two species, a flightless rail and a parakeet, were exterminated. The rabbits were stripping the island's vegetation bare.

In 1968, in an effort to control the situation, scientists introduced the Myxomatosis virus, which is lethal to rabbits, and the European rabbit flea, which spreads it.

By the early 1980s, the rabbit population had fallen to about 20,000. But the cats were hungry, and they began feeding on burrowing seabirds, threatening their existence.

Again, researchers intervened and began shooting the cats. By 2000, there were none left.

But to the researchers' surprise, the rabbits began proliferating again despite the presence of the virus. The animals have stripped as much as 40 percent of the island bare of vegetation.

The critters were even blamed for a 2006 landslide that wiped out part of an important penguin colony.

The next stage, Bergstrom said, could be an "ecosystem meltdown," in which the entire island's ecology is disrupted.

To prevent that, the scientists' only course is to eradicate the rabbits, mice and rats on the island, a process that could cost at least $16 million and take years.