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We’re aiming high with our Predator Free 2050 ambition. It’s a big goal, and a unique one. But everything we know about eradicating pests on the mainland, we learned on islands.

This is the seventh blog in Brent’s PF2050 series.

By Brent Beaven, Programme Manager Predator Free 2050

Image of Brent Beaven releasing tīeke/saddleback
📷: Peta Carey

Everything we know about eradicating pests on the mainland, we learned on islands.

In 1959, a small boatload of Forest & Bird volunteers bumped ashore on Maria/Ruapuke Island in the Hauraki Gulf and placed rat baits, the first tentative step on a journey that today sees Aotearoa as an acknowledged world leader in island pest eradications.

Ruapuke is tiny — just a couple of hectares — but it’s a landmark in conservation history as the site of the world’s first successful rat eradication.

It also inspired wildlife managers to much greater things. By applying lessons learned from smaller islands, they’ve been able to scale up their efforts and ambitions: in the 70 years since Ruapuke, pests of all kinds have been removed from more than 110 islands all around our coast, each one bigger than the last, culminating in subantarctic Motu Ihupuku/Campbell Island, at 12,000 hectares.

Pleurophyllum speciosum, great emporer daisy on Motu Ihupuku/Campbell Island
📷: John Barkla DOC

Rats, stoats and possums have driven many native creatures from the mainland altogether, so that pest-free islands are now the arks of Aotearoa. Without them, some species would have nowhere left to live.

They also make ideal testing grounds for new eradication methods, which makes them a key objective in the Predator Free 2050 Strategy.

On the mainland, a study site can be re-invaded by pests from surrounding countryside, making results difficult to measure. But there are no such difficulties on a remote island, giving researchers a much clearer picture of what works and what doesn’t.

To visit an island free of pests is to glimpse how Aotearoa looked and sounded before mammalian predators turned up. If you’re lucky enough to wake up at anchor off Manawatāwhi — the Three Kings Islands — hundreds of korimako/bellbirds will treat you to one of the best dawn choruses anywhere.

Korimako in the sun on Rangitoto Island
📷: Shellie Evans

Take a stroll at dusk on Hauturu-o-toi/Little Barrier and you’ll see the flitting figures of pekapeka-tou-roa, or long-tailed bats, against the fading light. Wētāpunga — giant weta — will be emerging from their hiding holes, and geckos will be climbing into the canopy to feast on nectar. The place comes alive.

On Takapourewa, or Stephens Island, in Cook Strait, dusk is when hundreds of thousands of seabirds return to their burrows, just as tuatara are emerging to hunt.

Tuatara in a log on Takapourewa/Stephens Island
📷: Sabine Bernert

Some Nature Reserves, like Kāpiti Island off the Horowhenua coast, are open to the public, and you can see native wildlife now rare or lost altogether from the mainland. On Kapiti, expect to be mobbed by kākā, see takahe leading their gawky chicks through the tussocks. The leaf litter twitches with the scurry of lizards. On Tiritiri Matangi, hear the chattering challenge of tīeke, or the gorgeous notes of the kōkako.

On a pest-free island, you realise how Aotearoa once rang with birdsong, and how the fragrance of blossom would have wafted everywhere on the air.

You can see how birds like kākāriki, kererū and kōkako once spent much of their day feeding on the ground, in complete safety. You can start to appreciate how diverse, intact ecosystems might once have worked.

In that sense, they offer us a glimpse of the future, too: of what we can expect the mainland to look and sound like once again, if we strive for a Predator Free 2050.

Male hihi on Kāpiti Island
📷: DOC

One of PF2050’s interim goals is to rid New Zealand’s remaining uninhabited offshore islands of mammalian predators by 2025, but there’s a hurdle in the way, called Maukahuka.

Part of the subantarctic Auckland Islands group, Maukahuka lies astride the Furious Fifties, 465 kilometres from Bluff. It stands in the path of some of the harshest weather and hugest seas Nature can muster — 46,000 hectares of desperate travel through dwarf forest, scrub and peat bogs. But as the fifth-largest island in Aotearoa, it’s biologically one of the richest in the subantarctic. The lower slopes are draped in southern rātā, stunted by the cold and the wind, but no less glorious in summer bloom.

The island’s open country should be rampant with megaherbs, but the ground is bare, ransacked by wild pigs. Released here in 1807 as sustenance for sealing gangs, pigs have had a devastating impact, eating the eggs and chicks of seabirds that would once have numbered in their tens of thousands. Between them, the mice and the cats, they’ve extirpated 32 bird species from Maukahuka, and wrecked an intricate nutrient cycle powered by seabirds.

Southern royal albatross on Motu Ihupuku/Campbell Island
📷: Danica Stent, DOC

The New Zealand subantarctics are a World Heritage site, recognised for their unique biodiversity. Maukahuka is the last of them to harbour pests, and if they were removed, it would add another 420 per cent of safe habitat for native biodiversity in the group — particularly the four species of albatross mostly confined to other pest-free islands in the group.

And while Maukahuka presents perhaps the toughest eradication challenge of all, field studies have confirmed it can be done. The pigs can be cleared using traps, aerial hunting and ground hunting with dogs. The mice will need a departure from standard practice, with aerial baits sown at half the usual rate, in summer rather than winter to exploit the short weather windows.

Cats can be dealt with by a species-specific toxic bait and ground hunting. All up, it’s expected to take ten years, and that’s why the 2025 islands target is the least likely of the PF2050 interim goals to be met.

Historically, island eradications have been ad hoc, assembling the necessary expertise, funding and equipment practically from scratch, and each successive project had to duplicate the process. It all took time and repeated investment. This year, all that changed with the establishment in DOC of a dedicated team of specialists.

The National Eradication Team (NET) will guide the clearance of our remaining islands with ecological and technical advice. Through feasibility studies, it’ll prioritise each island according to scale and its “defendability” — the likelihood of keeping predators off it once it’s been cleared. The NET brings a continuity of skills, and the co-ordination of resources to mount eradications more efficiently, with less duplication.

A predator-free Rakiura, or Stewart Island, is one of the most exciting prospects. Rakiura has always banked on its natural capital, and the gazettal of a national park there in 2002 put it on the itinerary of between 36,000 and 40,000 nature fans each year.

Rakiura Tokoeka, Brown Kiwi, Tin Range
📷: Mike Douglass

That’s because it holds a trump card: mustelids — weasels, stoats, ferrets — never reached there, which is one reason kiwi can wander about in broad daylight. On Ulva Island, in Paterson Inlet, people can see tīeke, mōhua, kākāriki and tītipounamu all in the space of a morning.

But the island’s forest is browsed by possums and deer, and rats and wild cats take a heavy toll on wildlife, leading in 2019 to the signing of a Memorandum of Understanding between the four Papatipu Rūnanga of Murihiku, us at DOC, Southland councils, Real Journeys and the New Zealand Deerstalkers’ Association to pursue a predator-free Rakiura. It would be the country’s biggest sanctuary, protecting highly endangered species such as kiwi, the tūtiriwhatu/New Zealand dotterel, and the tawaki, or Fiordland crested penguin. It would also allow for the return of species long since lost from the island, like kākāpo and kōkako.

In 2020, the project got a multi-year funding boost, which allowed eradication planning and design to begin.

Meanwhile, Predator Free 2050 Ltd has funded a feasibility study to inform Tū Mai Toanga, a proposed eradication project on Aotea Great Barrier Island, in the outer Hauraki Gulf, along with three staff. Tū Mai Taonga is also supported by the us at DOC, Auckland Council, sanctuaries and conservation groups.

So while the interim goal of having all eradications completed on offshore islands by 2025 may go unmet, an exciting new chapter in the story of island eradications in Aotearoa is opening: the fight against introduced predators has moved to those isles that people call home, too. That boatload of volunteers would never have dreamt, all those years ago as they set out for Ruapuke Island, that they were writing the open pages of such an inspiring tale.


To hear Brent talk about our Predator Free 2050 goal, have a listen to the DOC Sounds of Science Podcast, which is available wherever you get your podcasts.

#21 Banding banter DOC Sounds of Science Podcast

  1. #21 Banding banter
  2. DOC Sounds of Science bonus episode, the trailer

For more about the PF2050 strategy, including a run through of the tools that are going to get us there, visit https://www.doc.govt.nz/moving-towards-pf2050

New Zealand’s Predator Free 2050 goal — to eradicate rats, stoats and possums from the entire country by mid-century — is globally unique and unattempted. There’s no manual to guide us, no precedent to follow. How, then, do we make sure we get this right?

This is the sixth blog in Brent’s PF2050 series.

By Brent Beaven, Programme Manager Predator Free 2050

Brent Beaven, standing in front of trees
📸: Capital Kiwi

If we consider that PF2050 is a solution to a problem, then our first step is to try to understand the nature of that problem. People broadly recognise three kinds of problem: simple, complicated, and complex.

A breakdown

A simple problem is one that somebody’s solved before, so that they’ve already worked out the solution for you.

Clearly, PF2050 isn’t one of those…

A complicated problem is one you don’t know how to fix yourself. You may not even know what the problem is; you just know it’s in there somewhere. Let’s say your car’s engine is making a weird noise.

There are an awful lot of moving parts in an engine, and the problem could be any one of them, but the main thing about complicated problems is that there are experts out there who know how to fix them, even if you personally don’t.

Complex problems are more nebulous, because even experts can’t know all the forces at work in them. It follows then, that we can’t know the solutions, either. The vexing thing about complex problems is that trying to fix them often changes the nature of the problem itself — and our history in Aotearoa is full of these, more below.

So the only way to approach complex problems is to try something, and see what happens.

Maybe that will be something completely unexpected, but the trick is to learn from it before trying something else. The fancy name for this is “adaptive management” or “developmental evaluation”, but it’s really just careful, considered trial and error — giving the solution a way to emerge.

Nature and people

PF2050 means dealing with the most nebulous things there are — nature and people.

This will pose problems of all kinds, so it’s vital to take time to first understand which kind you’re dealing with, so that your response is the appropriate one.

A simple solution, for instance, won’t fix a complex problem. As proven throughout history, a simple approach is unlikely to work across diverse, complex ecosystems — precisely the sort where Predator Free will operate.

Ironically, it was this “applying the wrong solution to the problem” thinking that got us into this mess in the first place.

When the colonists brought stoats and possums to Aotearoa, they assumed they were dealing with a simple problem that could be fixed with simple, known strategies — the stoats would deal with the rabbit problem, and the possums would fix the lack of a fur trade. A prescient few saw the folly of these ideas, and pleaded for them to be abandoned, but a dogmatic cabal drove them through.

Even the naturalists couldn’t anticipate the carnage that followed, simply because nobody understood the stochastic nature of nature—i.e. random happenings or patterns that can be analysed, but are hard to precisely predict. In those days, people believed ecosystems followed certain laws, most of which gravitated inexorably towards some imagined equilibrium.

Lake Daniell Track trap on the forest floor
📸: Baptiste Maryns

In reality, they made a complex problem greatly worse: the intricacy of natural systems gave things ways to backfire beyond our most fevered nightmares.

Now, as we try to halt and reverse the harm of that kind of thinking, it’s important that we don’t unwittingly repeat it.

Learning by doing begins with the very premise that we don’t fully understand what we’re up against. We won’t succeed by pressing home a prescription on the assumption that it’ll somehow conquer the uncertainties.

It will come from treating every Predator Free project as a chance to learn more about those uncertainties. It will come, in fact, from getting things wrong occasionally. It will come from giving up some cherished beliefs and going back to the drawing board.

Our ambitious goal

Because Predator Free has a deadline, there’s an understandable sense of pressure for progress — to get some acreage ticked off right now, then to move onto the next.

But there’s a risk in that: we can’t stage-manage nature any more than the colonists could.

Snares Island mātātā/fern bird in the grass
📸: Brent Beaven, DOC

If we prioritise body counts over learning as we go, we’ll have no solutions for that inevitable occasion when Nature doesn’t respond the way we expect it to. The beauty of learning by doing — of reflecting on what went wrong and why — is that the lesson itself represents an objective met, rather than a failure suffered.

At present, there are 19 regional PF2050 projects. Each one should rightly be regarded as an experiment in breakthrough science.

Yes, the clock is ticking, but we shouldn’t feel too pressured for results just yet: we can — and should — spend half our effort and resources over the next 10 years on innovation and learning, through science and matauranga — testing as many different designs and methods as we can.

Campbell Island Teal standing on rocks
📸: Brent Beaven, DOC

Finally, we spend the balance doing — eradication projects across the full gamut of environments, the better-informed for that early trial and error.

It becomes clear that a complex problem like Predator Free lies well beyond the mandate — or the resources — of any one agency to solve.

Which is why a solution can only come from truly national collaboration between all sectors of society, business and governance. And from a willingness to accept that, if at first we don’t succeed, we do our best to figure out why …

And then we try again.


To hear Brent talk about our Predator Free 2050 goal, have a listen to the DOC Sounds of Science Podcast, which is available wherever you get your podcasts.

#21 Banding banter DOC Sounds of Science Podcast


For more about the PF2050 strategy, including a run through of the tools that are going to get us there, visit https://www.doc.govt.nz/moving-towards-pf2050

Occasionally, you may hear someone say: ‘1080’s not working. We’ve been using it for 60 years, and we’ve still got possums’. Which might sound like a fair comment, but it fails to recognise a crucial reality: pest control and pest eradication are two very different things. This is the fifth blog in Brent’s PF2050 series.

By Brent Beaven, Programme Manager Predator Free 2050

Brent Beaven and tīeke/saddleback
📷: Peta Carey

Pest control is a bit like mowing your lawn: you don’t intend to remove the grass entirely — you just mow it regularly to stop it getting away on you.

Around one-eighth, or 12.5%, of the public conservation estate receives pest control in any given year, and sites are treated at intervals calculated to stop rats, possums and stoats reaching overly destructive numbers.

In forests with lots of food, which support high pest numbers, that might be every three years or even sooner. In less productive forests, that might be every five years.

Beech Forest, Milford Track
📷: Keri Moyle

Now imagine for a moment that you only mowed one-eighth of your lawn once a year, and that you mowed a different eighth each year. What would the grass on the other seven-eighths of your lawn do under such a regime?

This why we still have possums, despite decades of 1080 use.

Sticking with the lawn analogy for a bit, we all know that mowing is a bigger job in the spring and autumn, when conditions are right for grass to thrive.

Similarly, conditions in the forest occasionally become ideal for pests — times when there’s so much food around that they can breed up to their maximum potential. Periodically, whole forests simultaneously produce vast amounts of flower and seed, a phenomenon ecologists call a mast.

For example, when beech trees experience a cool summer followed by a warmer one, they can litter the forest floor between March and June the following year with up to 50 million seeds to a single hectare, many times more than usual.

The magnitude of masts varies across locations and from year to year, but in 2019, beech trees masted pretty much everywhere. So did podocarps — rimu, tōtara, kahikatea, mataī, etc — and in some places, tussocks, in what ecologists called a ‘megamast’.

In times of such abundance predator numbers go through the roof, and that has dire consequences, because once all that seed has either been eaten, or has germinated, plagues of hungry pests need something else to eat. They turn on native wildlife, often just when birds are trying to breed.

Mast seasons come along, on average, every four or five years.

Predator Plague Cycle diagram
✏: DOC

DOC runs a national predator control programme called Tiakina Ngā Manu (formerly Battle for our Birds).

Predator control across large landscapes or remote and rugged terrain costs a lot of money: in 2014 when the Battle For Our Birds predator control programme was launched, it was with a budget of $21 million over five years. Had we met the threat in all affected forests in that period, it would have cost around six times as much.

When a mast loomed in 2017, we had to seek an extra $21m in funding from Treasury to blunt the impact of the mast in addition to the initial five year funding package.

In 2018, within the context of the recently adopted Predator Free 2050 goal, the government increased the budget for Tiakina Ngā Manu to $81.2 million over four years, recognising an ongoing programme of predator control was needed in areas with high ecological values. The programme juggles resources when mast years occur to meet immediate needs while continuing to protect highly threatened native species populations in key areas.  

Which is all to say: possums, rats and stoats are costing the country a small fortune.

Willowbank kiwi chick
📷: Sabine Bernert

It’s estimated that invasive predators do more than $450m of damage to the crop and timber industries each year (as laid out in a 2015 BioScience paper). But arguably the biggest toll never appears in the Treasury ledger: Landcare’s John Innes has estimated that every year they devour around 26 million native forest birds chicks and eggs.

Just like mowing lawns, pest control is a job for life — a never-ending game of whack-a-mole that can only ever hold a line in the sand.

Imagine instead if we could rid Aotearoa of stoats, rats and possums completely — forever.

Picture a forest where a mast season was a bonanza for native wildlife, instead of a disaster.

Kākāriki on Enderby Island, Auckland Islands
📷: Jack Mace, DOC

That’s the proposition of Predator Free 2050 (PF2050), but eradicating pests is a whole other magnitude of difficulty and expense.

Back in 2008 I was working on Rakiura/Stewart Island, and did a study on the potential to eradicate invasive predators from the island. At the time, I estimated it would cost between $35 and $55 million to remove invasive predators from Rakiura/Stewart Island alone. That’s between $210 and $330 a hectare, as opposed to aerial pest control, which can cost as little as $20 a hectare.

It sounds expensive, until you factor in the perpetual price of having these predators in the country. At some point, PF2050 would start paying for itself.

So how much would it cost to eradicate predators from all of Aotearoa?

Even if we apply the highest known per-hectare cost — $993 per ha on Rangitoto and Motutapu Islands in the Hauraki Gulf — and a long-run inflation rate of 2.55%, the bill for PF2050 has been calculated at a little over $9 billion over 50 years.

New-generation traps and detection devices are already bringing that cost down, because they reduce labour. By way of comparison, control agencies expect to spend about $15 billion just trying to contain — not eradicate — all known agricultural pests over the same period.

Kākāpō chick in Invercagill. There are only 208 kākāpō alive today.
📷: Liz Carlson

When they deducted the known costs of invasive predators in New Zealand, and added the expected hike in tourism spending that being predator-free would bring, the authors of this 2015 paper found that PF2050 would deliver a net value of $9.32 billion over 50 years, well into the profit side of the ledger.

We’re not yet able to say conclusively how much it will cost to achieve Predator Free 2050 — and that’s mostly because we’re putting a focus on developing the technology and exploring new innovations that will allow us to do the job. Once we are further down the path with this tech, we will be able to cost it.

That said, some things, though, are beyond price: the greatest value of all would come from saving our native biodiversity from extinction, having it thrive, and for our children’s children to be able to experience it.

Doing nothing would be far too costly.

Ngā mihi

Brent Beaven


For more about the PF2050 strategy, including a run through of the tools that are going to get us there, visit https://www.doc.govt.nz/moving-towards-pf2050