In an attempt to save the seabird species Henderson Petrel from extinction on its native South Pacific island, one conservation group is embarking on a mission to eradicate a group of non-native rats that prey on the endangered birds.
Henderson Island is an uplifted coral island that is a part of the United Kingdom's Pitcairn Islands. A World Heritage Site, the island is remote and uninhabited, with a unique array of wildlife, including large numbers of breeding seabirds and land birds.
But although the island is mostly untouched by humans, the presence of rats is threatening the survival of many of the island's native species.
Unique, endangered wildlife
On Henderson Island, there are four bird species and nine plants found nowhere else on Earth. There are dozens of invertebrates, including eight Henderson snails, which exist nowhere else on the planet. It is a critical nesting site for 12 different seabird species — including four types of petrel — as well as for marine turtles.
"Henderson Island, in the central Pacific, is one of the most remote places on Earth. But its wildlife are not immune from problems," said Tim Stowe, the international director of the Royal Society for the Protection of Birds (RSPB). "Non-native Pacific rats, which were introduced by Polynesian settlers, have been ravaging the island’s wildlife."
The introduced Polynesian rats (Rattus exulans) are eating an estimated 25,000 petrel chicks every year — about 95 percent of chicks are eaten within a week of hatching — and compete with the native birds for food. At least four species of land bird and four of seabird have vanished from Henderson Island since the rats' arrival.
The RSPB is undertaking a project to stem the tide of bird loss.
"Once the rats are removed, we expect to be able to stand back and watch the Henderson petrel population recover from 16,000 pairs today back up to 1.7 million pairs within 70 years," said Jonathan Hall, a project officer with the RSPB.
Removing the rats
The operation will begin in August 2011. A team of contractors and their equipment, including two helicopters, will be brought in by ship.
The RSPB will be following a method pioneered in New Zealand to clear the large islands of bird-eating rats.
"This involves using helicopters to methodically drop poison bait pellets across the island using GPS-guidance," Hall told OurAmazingPlanet. "This is the only way to have a high level of confidence of success — it would not be possible to reach all the rats via a ground-based operation on this 14.3 square-mile (37 square-kilometer) island."
"After one complete drop, there will be a pause of 10 days, and then the process will be repeated as a second insurance drop to ensure that all the rats are removed," Hall added. "Over 300 islands have been successfully cleared this way, and we have undertaken rigorous planning for the last three years, so we are confident of success."
There are no other mammals on Henderson Island, so there is no danger of the pellets harming anything other than the intended target. In addition, certain bird species on the island will be taken as a captive population for the duration of the operation so they will not be harmed and 'scarer' measures will be put in place on the beaches to deter shorebirds.
The RSPB will be monitoring the island again in 2013 to determine if the project was successful. The group must wait at least two years until any remaining rats increase to a number where they become detectable.
"Massive long-term benefits will be achieved from this short intervention, the whole ecosystem will benefit — the endemic land birds, invertebrates, flora and even nesting green turtles," said Hall. "Once the seabird population recovers, this will re-establish the marine nutrient cycle."
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