Every day, our precious native species are ravaged by predators such as possums, stoats and rats. Getting rid of these pests may sound far-fetched, but as Jamie Morton reports, so did the idea of conquering Mt Everest.

In our forests, islands, farms and wetlands, the country is at war.

Hundreds of millions of taxpayer dollars are being poured into the never-ending struggle, waged against non-native pests that kill 26 million native birds every year.

And if there was any doubt our pest management effort is a war, consider the militaristic phrases used by officials, academics and conservationists taking on the fight: rolling fronts, re-invasions, beachheads.

In recent years, the question of final victory has gained increasing attention.


"It's crazy, it's ambitious, but I think it might be worth a shot," Sir Paul Callaghan declared last year, at a public lecture that would be the physicist's last.

The Prime Minister's chief science adviser, Sir Peter Gluckman, couldn't disagree. "Of course it's conceptually possible," he told the Herald. "But is it practically possible for the whole of New Zealand? It's a matter of how much you are prepared to put into something."

Flashback to 1960, when, using a 5 grant from the Department of Internal Affairs and working in collaboration with a young ranger named Don Merton, Forest and Bird completed the world's first recorded successful rat eradication, on the 1ha Maria Island in the Hauraki Gulf.

Now the country is running out of offshore islands to liberate from pests.

In the past decade, the Department of Conservation cleared rats from Campbell Island (11,000ha) and Secretary and Resolution Islands (23,000ha combined).

Today, most of the 31 species of exotic mammals, except for a few exotic species including birds and others, have been wiped out on these smaller islands.

The species specifically targeted - mice, rats, rabbits, hedgehogs, cats and possums at Rangitoto/Motutapu, pigs at Kapiti and goats on Great Barrier Island - are no more.

The obvious next steps are D'Urville (16,782ha) Great Barrier (28,510ha) Chatham (90,650ha) and Stewart (173,500ha).


The ultimate dream: a predator-free mainland, all 26 million hectares of it. If the present trajectory continues, there is the exciting possibility this could happen by 2050.

Campaigning economist Gareth Morgan, who is leading a charge to liberate Stewart Island of predators, has even set a deadline: Waitangi Day 2040.

Facing this lofty ambition are the obvious practical hurdles: scale, cost, technology, and social and political will.

A recent edition of Landcare Research publication Kararehe Kino described scale as a key problem, not just in regard to target populations of pests, but topographic complexities, habitats and natural foods, and the challenges of the so-called "rolling front" strategy that would likely be adopted where large areas of land were concerned.

Re-invasion of cleared areas would call for constant efforts to consolidate gains.

Despite some views that the weapons to win the war already exist, Landcare Research's research portfolio leader for weeds, pests and diseases, Dr Andrea Byrom, believes achieving pest-free status cannot be done with our present capability.

Methods such as aerial baiting with an anti-coagulant could put all rodents at risk in one event, but there is no tool to kill all other species of pests in a single application.

Possums, cats, rabbits and stoats could survive each offensive and would have to be killed to the last animal.

The cost of national eradication would be gradual, but likely, ultimately staggering. Cleaning out Rangitoto/Motutapu, even after possums and wallabies had been dealt with, cost $3.5 million, and by extrapolation the sum for the rest of the country has been put at $24.6 billion.

Dr Byrom and other experts have taken a stab at putting a price tag on the great goal, but she acknowledged this failed to account for the variable of advances in technology, which could mean cheaper and more effective solutions.

"And I think putting a dollar figure on it isn't actually the point, anyway."

The real goal is to get Kiwis behind the cause.

"A lot of thinking will have to be done around how we socialise this idea with the public," Dr Byrom said.

"The bottom line is there is a huge problem in this country with the threat from pests to our native biodiversity, and I think the best value this Predator Free New Zealand movement can have is making the public aware of that problem.

"That cannot possibly do any harm - these animals are out there killing native wildlife in our forests and wherever else, every day and every night, 365 days a year."

The Department of Conservation isn't looking at the idea half-heartedly either.

"It's something that certainly is a big stretch for us now, but it wasn't that long ago that we couldn't eradicate pests off the offshore islands, and now we've managed to pull that off on increasingly large islands," said Alastair Bramley, technical development manager of DoC's science and capability group.

A rolling front campaign could begin on an exposed beachhead and gradually work inland, with improvements and adoptions of new methods made along the way.

"It's very unlikely we are going to target all pests everywhere, because that's just ridiculous. Where do you stop?"

Like Dr Byrom, he saw the biggest battle in working with communities.

"Because most of DoC's historical pest elimination has been done where people don't live, how do we make it work for the communities which live in and around those pests?"

The lessons learned from the Stewart Island effort, which the department is working closely on, could eventually be applied to the mainland when the time comes.

If New Zealand could free itself of predators such as stoats, rats and possums, he had no doubt there would be an explosion of wildlife across the country.

When Captain Cook and his crew first arrived off our shores in 1769, the dawn chorus of birdlife was described as deafening.

But Mr Bramley said the country would never be that way again - and roughly a third of our native bird species have perished since that day.

The conservation win would however still be huge for New Zealand - and not just for the birds.

"We would end up with a lot more things for tourists to see when they arrive here, but secondly, it's the whole clean, green image thing."

Research was under way by Lincoln University to quantify the benefits, which University of Auckland ecologist Dr James Russell could only describe as "unimaginable".

To the agriculture sector, which undertook most possum control to prevent the spread of bovine tuberculosis, a disease which reaped $2.5 billion in damage to the sector, the gains would be huge.

Kevin Hackwell, Forest and Bird's advocacy manager, was just as optimistic.

"Decade after decade, successful improvements that we have been able to achieve have been based on better understanding of predator ecology, and refining our methods of delivering the baits to the pests," he said.

"Already there are new refinements that are being developed that will drive the next step of this initiative.

"We realise that a key challenge to achieving a predator-free status for the whole country will be carrying out effective eradication in populated areas of farmland and then the cities - something we have little experience of. However, some other countries already have carried out successful rat eradications in populated areas and we will be able to learn from their experiences."

The UK was beginning to realise the worth of driving rats from islands, while on the vast South Georgia Island, near Antarctica, rats and mice were being cleared one glaciated valley at a time, using similar methods to those that would have to be employed over such large areas as the North and South Island.

Dr Russell looked at the dream as being one akin to the first flight, or the conquest of Mt Everest, both feats regarded as impossible, and both which Kiwis could claim an association with.

"I believe it would give us all a sense of pride that we could do something great, as a nation, together, rallying us once again as Sir Edmund Hillary did in 1953," he said. "That everyone is talking about the concept, even if they don't know how it would be done, is the most encouraging sign overall - that we want to do it, even if we don't yet know how we will."