Ascension Island: No place like home

Imported cats led to the decline of the booby on Ascension Island. Michael Brooke reports on an ambitious plan to cull the alien species

For the first time in living memory, young boobies, tropical gannet-like sea birds, are due to fledge from Ascension Island in the tropical Atlantic. The first flight, due this month, is good news for the global campaign to undo the damage caused when alien species are introduced to remote regions of the world where they do not naturally belong.

For the first time in living memory, young boobies, tropical gannet-like sea birds, are due to fledge from Ascension Island in the tropical Atlantic. The first flight, due this month, is good news for the global campaign to undo the damage caused when alien species are introduced to remote regions of the world where they do not naturally belong.

Worldwide the problem posed by alien species is huge, both economically and in terms of damage to native wildlife. It is estimated that it costs $100bn each year for the United States to deal with direct and indirect damage caused by the estimated 50,000 alien species introduced to the North American continent.

Ascension, a barren 97sq km (37sq miles) speck of land that forms a vital staging post on the flight from the UK to the Falklands, was once home to immense sea-bird colonies. The legacy is evident today in the guano of yesteryear, which still extends over about 15sq km because it has never been washed away in the island's arid climate. Unfortunately, in 1815, cats were introduced by the British garrison to control rats – which were another introduced species. Having failed to read the script, the cats not only lunched on rats but supped on sea birds, and soon the vast colonies disappeared. Boobies and other sea birds were banished to small precipitous rocks off Ascension.

Following 40 years of campaigning by conservationists, the British Government announced in 2001 that £500,000 would be allocated for ecological restoration on Ascension, which is a British Overseas Territory. The main part of the restoration programme was eradication of feral cats from the island. In supporting the programme, the Government is honouring a commitment under the international Convention on Biological Diversity to "control or eradicate those alien species that threaten ecosystems, habitats or species".

New Zealanders are acknowledged world leaders in the business of putting islands to ecological rights. A team of eight under the leadership of Mike Bell of Wildlife Management International arrived on Ascension in early February. "It was important that the island's 1,000-strong population, a mix of St Helenans, expats, and service personnel, supported the programme. So we held public meetings to explain what was going on. This was a vital pre-cursor to neutering all domestic cats and implanting them with electronic tags to ensure that nobody's pet cat got caught up in the cull. We also consulted with welfare organisations to ensure that our methods were as humane as practicable," says Bell.

Since January around 500 feral cats have been killed using a mix of shooting, poisoning and trapping. Now Bell thinks only a handful of feral cats remains. To flush out this wily few, special baits have been brought to the island – day-old chicks from South Africa. All the domestic cats are wearing reflective collars to ensure that marksmen target only uncollared cats.

"It is really exciting that birds are now nesting, even before complete eradication of the cats," says Jim Stevenson, the International Officer of the Royal Society for the Protection of Birds, who has managed the project on behalf of the UK Foreign Office. "We will monitor the situation over the coming months and years to ensure no young cats emerge."

Once feral cats are gone from Ascension, it will become the second largest island in the world where introduced cats have been eradicated. (The largest island is the 300-sq km Marion Island in the Roaring Forties where a five-year shooting campaign supported by the South African Government eliminated cats in the early Nineties.)

Conservationists hope the Ascension rats can be eliminated next. The £1.5m project will require satellite-guided helicopters to distribute poisoned bait across the island. "We will only go ahead with this project once we can be confident that Ascension can remain rat-free forever. But the benefits to people, to smaller sea birds, to the island's unique creepy crawlies and, perhaps, to plants could be huge. Most importantly, it is a way we can hand over a world richer in wildlife to the next generation," says Stevenson.