One of the world’s most important atolls cleared of rats

Henderson Island with view of project vessel MV Aquila in background, Henderson Island. Photo credit Richard Cuthbert.

December 2011. A ground-breaking £1.5million RSPB project to eliminate introduced rats from an uninhabited island in the central Pacific has attempted to remove the fingerprints of man from an otherwise idyllic tropical paradise. As a bonus, the project has also increased the known size of the UK's overseas territories by six square kilometres.

Henderson Island
Henderson Island, one of the UK's most remote territories and a World Heritage Site, has been ravaged by Pacific rats, introduced by the Polynesians eight centuries ago. The rats were destroying the island's habitats, driving the endangered Henderson petrel - a rare seabird confined to the island - to extinction, and significantly damaging the populations of four other bird species, rare plants, insects and snails all found nowhere else on earth.

Millions of sea-birds - Almost all gone
There were millions of ground-nesting seabirds on Henderson before rats were introduced to the island, but their numbers have been reduced to just 40,000 pairs today. Early results indicate that the seabird population will boom if the rats have been successfully removed.

The mission - a partnership with the Pitcairn Islands Government - was one of the most complicated the RSPB has ever undertaken, and involved a voyage of 27,000 kilometres in a purpose-built aircraft carrier, capable of handling two helicopters from its temporary flight deck. The Society hopes to have removed introduced rats from Henderson Island by dropping poison rat pellets from giant hoppers suspended beneath the choppers with sufficient accuracy to land a few feet apart across the entire island, which is 32 times larger than Hyde Park.

Henry Bellingham, Minister for the Overseas Territories, said: "I am extremely encouraged by the initial indications that this programme has had a significant impact on protecting the Henderson petrel and the invaluable biodiversity of Henderson Island. I was pleased that the UK Government was able to work so closely with the RSPB, the Pitcairn Government and others on this important and pioneering project."

Environment Minister Richard Benyon said: "The rats on Henderson Island pose a serious threat to native wildlife. The RSPB have been working hard to remove them before treasured wild birds, particularly the Henderson petrel, are lost forever. Defra contributed £200,000 towards this important project, helping the RSPB to halt the decline of these endangered birds before it is too late."

Dr Richard Cuthbert is an RSPB scientist who has been involved with the project and spent three months on the island during the operation along with a project team from the UK, New Zealand and Pitcairn Island. Commenting on the threats posed by rats, he said: "Without action to remove the rats, the rodents would have eventually driven the unique Henderson petrel to extinction as the rats eat this seabird's chicks alive. The RSPB wasn't prepared to stand by and let this happen, especially as the island is a responsibility of the UK.

"The rats were eating an estimated 25,000 seabird chicks each year and over time had reduced the seabird population from millions of breeding pairs to just 40,000 today- a number that is still declining. Having completed the operation we now have to wait for two years to be certain whether all the rats have gone. But there are encouraging signs that the island is returning to a natural state.

Murphy's petrel
"Before the eradication attempt, almost no Murphy's petrel chicks escaped rat predation. The latest surveys suggest that since the drop, over 85 per cent of Murphy's petrel chicks have gone on to fledge- a truly astonishing result which shows the devastating impact of the rats. The Henderson reed-warbler has also responded extremely quickly, with counts revealing a five-fold increase since the bait drop. Very few conservation projects have the potential to show such dramatic results.

Jonathan Hall, the RSPB's project coordinator commented: "The UN World Heritage Committee had urged the UK to restore the island by eradicating the rats, but we knew that the project would be among the most challenging conservation projects ever undertaken as every single rat needed to be removed.

Island's moved and grew during the survey!
"Henderson Island is so remote and so little surveyed that during the operation we discovered that we had increased the known size of the island by six square kilometres and moved its position by over a kilometre. The project's helicopters flying with GPS equipment found that the island was 15% larger than anyone realised and in a different position to the marine charts. It's not every day that you get to increase the size of the UK's territories!"

Covering 43 square kilometres, Henderson Island is over 3,000 miles from the nearest mainland in South America. It is the world's only forested atoll with its ecology virtually intact, and the largest tropical or sub-tropical island ever subject to a rat eradication attempt. Although the results won't be known until 2013 - when rat surveyors visit the island - the RSPB remains extremely hopeful that the project has eradicated rats from the island, as no previous aerial operation to remove Pacific rats has failed.

Non-native species, such as rats, have been one of the greatest drivers of extinction of birds, especially on remote islands where the native wildlife has evolved in isolation away from predatory mammals. Although it's too late for some now-extinct species, the RSPB hopes that the project has thrown Henderson Island's unique wildlife a lifeline, including four species of landbird found nowhere else on earth: a fruit-dove; a lorikeet; a reed-warbler and a rail: a relative of moorhens and coots.

Dr Tim Stowe is the RSPB's International Director. Commenting on the operation, he said: "This is a chance to wipe the fingerprints of man from such a large island. We are hopeful that within several years the island will be completely transformed as the forest recovers, seabirds return, insects boom and turtles hatchling will be able to crawl to the sea without fear of rats. No-one alive has seen the island in this state, and the Pitcairn community and our scientists will be among the first to see this ecological time capsule."

The RSPB's sincere thanks go to our project partners, the Pitcairn Islanders, as well as the UK Government, the David and Lucile Packard Foundation, the Critical Ecosystems Partnership Fund, BBC Wildlife Fund and the Royal Zoological Society of Scotland. We've raised almost £1.5million to cover the cost of this operation and allow us to proceed, something which we could simply not have achieved without the support of Sir David Attenborough, seabird expert Peter Harrison, and all our generous donors.

The 27,000-mile voyage across the Pacific also included rat eradication projects on Palmyra Atoll and in the Phoenix Islands conducted by other organisations. This project was the first multi-island, multi-nation, multi-agency rat eradication voyage ever attempted.