Books: eradicating uninvited pests

In William Stolzenburg’s Rat Island, Clive Cookson finds an uplifting tale of the struggle to restore pristine habitats that have been overrun by non-indigenous animal predators. Remarkable results have been achieved.

Rat Island: Predators in Paradise and the World’s Greatest Wildlife Rescue
William Stolzenburg
Bloomsbury, 2011

Ecologists are warning with growing urgency that Earth has entered its sixth mass extinction of living species. While the first five were caused by asteroid impact or volcanism on a vast scale, human activity is responsible for this one.

The current extinction is taking place at an uneven pace across the world and, as the American wildlife writer William Stolzenburg shows in his gripping new book, islands are suffering most. Islands have produced 20% of Earth’s animal species on 5% of its landmass, but two-thirds of the birds and reptiles lost over the past 3,000 years have been insular species. Today they harbour almost half of the world’s critically endangered species.

Though there are all too many examples of animals wiped out directly by people slaughtering them for food, most of the damage has been an indirect result of human settlement. Deliberately or otherwise, explorers and settlers introduced all manner of animals to pristine islands. Rats, mice, cats, foxes, ferrets, weasels, pigs and goats have all feasted on native flora and fauna such as flightless birds, which had evolved no defence against alien predators.

But Rat Island is less a tragedy of paradise lost than an uplifting tale about the heroic struggle to regain indigenous habitats by exterminating the unwanted predators. The campaign, which began sporadically in the mid-20th century, is gathering pace and showing some remarkable results. It turns out that the ragged remains of native fauna and flora often regenerate rapidly when the pests are out of the way.

Rat poisoners, fox shooters, cat trappers and others have rid islands across the globe of alien predators, from the sub-Antarctic seas south of New Zealand, through the tropical Pacific west of Mexico, up to the Bering Sea between Alaska and Siberia.

Stolzenburg describes vividly the bravery and dedication required to exterminate pests from rocky storm-lashed islands in the far northern and far southern oceans. Take Campbell Island, a “44-square-mile [113-square-kilometre], starkly beautiful, foul-weather paradise” bounded by 300-metre cliffs and lying about 800 kilometres below New Zealand’s South Island.

In 2001 a battle flotilla — Rat Island is full of military language — of five helicopters and two ships loaded with 132 tonnes of the rat poison brodifacoum reached Campbell Island. Peter McClelland, the mission’s director, had planned the invasion for five years.

“It would be a blitzkrieg without compromise,” Stolzenburg writes. “If one pregnant rat were left in one little cranny of Campbell’s rugged enormity, future eradications, careers and $2 million of taxpayers’ money would be lost. Failure was not to be discussed.”

In the event, every one of the estimated 200,000 Campbell rats — descendants of animals introduced unwittingly by seal hunters 200 years earlier — died. McClelland found it hard to believe his success: “I looked at those cliffs and the size of that island and I said, ‘No, there’s no way we did that. It was too big, too rugged to get rats off that island.’ ” The eradication of rats has led to an avian renaissance. Seabirds are returning and landbirds such as Campbell Island’s native duck and snipe appear to have been rescued from the brink of extinction.

But Rat Island is not a wholly triumphant tale. Some animal-welfare groups have opposed the extermination of alien species on the grounds of cruelty — and some ecologists are concerned about the collateral damage from mass poisoning. Thousands of dead and dying rodents are tempting, but toxic, meals for other species, which might then die in turn.

Stolzenburg got the title of his book from Rat Island in the Aleutians, where 46 tonnes of poison were dropped in 2008. Collateral damage there included 420 poisoned birds, among them more than 40 bald eagles — the avian emblem of the United States. Although the overall ecology of the island is likely to benefit enormously in the long run, the dead eagles are a weapon for those arguing against similar action elsewhere. But most readers of this powerful book are likely to agree that the campaign should continue to rid islands of introduced pests that threaten native wildlife.

Clive Cookson is the Financial Times science editor.

© Copyright The Financial Times Limited 2012