Ecologists hail victory over Galapagos invader

Like a jewel set in the azure expanse of the Pacific Ocean, the Galapagos Islands have epitomised the splendid yet delicately-balanced beauty of nature. For more than two centuries their rare and unique wildlife – once the inspiration of Charles Darwin – has been under threat from alien species brought there by man. Now the archipelago has won a rare victory against the relentless forces of extinction.

Conservationists have declared one of the biggest islands of the Galapagos free of the destructive feral pig, which was introduced by mariners more than 130 years ago. Until now, thousands of feral pigs had been eating their way through the eggs of the endangered giant tortoises, seabirds, lizards and turtles.

This weekend, a campaign to eradicate the feral pig from the uninhabited island of Santiago was officially declared a success, marking a turning point in the global initiative to preserve the native species of this World Heritage Site.

It also marks a critical reversal in Santiago's misfortune. When Darwin stayed on the island for two weeks in 1835 he saw no pigs. But a British mariner called Commander Cookson reported huge numbers of them 40 years later.

The feral pig is just one of many alien species humans have introduced to the islands, but it is one of the most destructive. A single pair of pigs can destroy more than 20 tortoise nests in one month and, with no natural predators, the only limit to the pig population was the availability of food.

Scientists calculated that the survival chances of young tortoises on Santiago were, in effect, nil because of predation by pigs, which also raided the nests of ground-dwelling seabirds and turtles.

The situation was so bad that in 1970 scientists from the Galapagos National Park and the Charles Darwin Foundation set up a captive breeding programme for giant tortoises. Thirty years later, nearly 500 young tortoises had been repatriated to Santiago.

Meanwhile, in 1973 the pig-eradication campaign began. By 1996, teams of hunters armed with guns and specially trained dogs had tracked and shot nearly 19,000 pigs. In the last few years their efforts were redoubled with the help of satellite navigation and computerised maps to cover every square metre of the island.

The last pig to be captured on Santiago was in November 2000, more than a year after the hunters had made an extensive search of the island without finding their quarry. For the past 18 months scientists have monitored baited traps on Santiago for further evidence of pigs and are now convinced that none exists.

"The plan to eradicate the feral pig has been executed. There are no more pigs on Santiago," Dr Felipe Cruz, the technical director of the project at the Charles Darwin Research Station, said, speaking on a satellite phone from the remote archipelago.

"Now we have proved that we can eradicate feral animals from an island the size of Santiago. It is the largest island in the world to be cleared of feral pigs," he said.

Already, the scientists are beginning to see a reversal in the fortunes of the archipelago's many endemic species, such as the rare Galapagos snake and larva lizard. For the first time in many years, the Galapagos rail and dark-rumped petrel, two ground-nesting birds, have increased their breeding populations.

Leonar Stjepic, the director of the Galapagos Conservation Trust, a charity based in London, said the success with feral pigs will be an inspiration for the other campaigns aimed at eradicating alien species from the islands.

"A landmark has been reached in Galapagos and its success is testament to what can be achieved through well-spent resources and commitment," Ms Stjepic said.

"With continued funding the same can be achieved on Isabela Island where goats are destroying the habitat and endangering wildlife," she said.

The goat problem on Isabela, the largest of the islands, is every bit as important as the eradication of feral pigs on Santiago. About 80 per cent of all the Galapagos' giant tortoises alive today live on the northern part of Isabela, which had never seen a goat until they were introduced to the islands by whalers and other mariners who wanted a supply of fresh meat. They have since spread rapidly, leading to severe overgrazing. On Isabela alone, an island about 95 miles long and 16 miles wide, scientists estimate there could be up to 100,000 goats competing with the giant tortoises for the increasingly sparse vegetation.

Ridding Isabela of its goats poses a far bigger problem than the elimination of pigs from the smaller island of Santiago, Dr Cruz said.

Each hunting dog used on Isabela is trained not to attack the animals but to drive them towards the guns. The Isabela hunters are now using techniques developed on Santiago against pigs. "In the past, hunters would split up and work different parts of the island, but hunters are now all hunting the same block of land in a line formation around 100 metres apart," Dr Cruz said.

If nothing is done about the goat population, scientists estimate they will increase to a maximum population of about 500,000 individuals and will quickly convert ancient forests, which are rich in birdlife, to relatively barren grasslands. The loss of forests will cause greater erosion on the steep volcanic slopes, leading to the permanent loss of soil that has taken hundreds of thousands of years to form.

Despite this being the most ambitious eradication of an alien species yet undertaken on such a large island, the conservationists are convinced it can be done, providing there is a stable financial commitment from the funding bodies.

Nearly 200 years after Darwin spent a part of his formative years exploring the Galapagos, the archipelago is entering perhaps the most decisive phase in its one-million year history.

Island pests

Doves: Brought to the islands on ships, they are known to spread diseases to other birds, including the Darwin's finches.

Rats: Have been carried to the four corners of the globe as stowaways. They eat birds' eggs, tortoise hatchlings and just about anything else.

Feral cats: On several of the islands, escaped cats have become a particular problem, given the ease with which they can catch birds, lava lizards and marine iguanas.

Smooth-billed ani: Belonging to the cuckoo family, the ani was brought to the Galapagos in the hope that it would eradicate ticks on cattle. In fact it eats ticks everywhere it lives except in the Galapagos.

Fire ants: Brought to the islands with imported vegetation, fire ants have proved a resilient pest and highly destructive to endemic birds and other insects.

Quinine tree: Famous for its anti-malarial properties, the tree has formed lush forest cover at the expense of many native plants.

Dogs, donkeys and cattle: Many domestic species that have escaped have wreaked havoc on the delicate Galapagos ecology. Dogs eat wildlife, donkeys and cattle trample on plants.