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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.

Episode 14: Predator Free and me (part two) 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

To meet the high bar of Predator Free 2050, there can’t be any laurel-resting. Here’s a run through of some of the exciting things happening in the PF2050 space. This is the fourth blog in this PF2050 series.

By Brent Beaven, Programme Manager Predator Free 2050

Ship rat and land snail
📷: Ngā Manu images

The Predator Free vision calls for the complete removal of rats, stoats and possums from Aotearoa. We have to take action, they’re causing serious damage.

It’s no small task: these creatures have evolved masterful survival and breeding strategies, honed by millions of years of evolution. If we’re to eradicate them, we’ll need to find their Achilles Heel — some physiological or behavioural trait we can leverage in our work.

That means understanding intimately the things that make them tick: their metabolisms, their motivations, and their fears.

This year, that understanding took a big leap forward when researchers announced they had mapped the entire genome of the ship rat, one of our most destructive pests.

A genome is an organism’s complete set of DNA, including all its genes. A ship rat has around 25,000 of them and knowing what each one does will help us better understand how ship rats disperse, and to develop species-specific toxins.

The genome of the Norway rat — another important predator in New Zealand — had already been mapped, and in July, Manaaki Whenua Landcare Research scientist Dr Andrew Veale announced that his team has also sequenced the stoat genome. Stoats can be especially difficult to trap, so this intimate knowledge of their physiology will be a huge asset as we continue work on a stoat-specific toxin.

Personality matters

Meanwhile, other teams are focussed on predator personalities.

Presently, pest control typically removes around 95% of a target population, but that’s not enough to achieve the Predator Free goal of eradication. Researchers suspect that the 5% of predators that remain may have an intrinsic distrust or fear of traps and/or poison baits.

Trap set on the Lake Daniell Track, baited with an egg
📷: Baptiste Maryns

A big risk of leaving them behind is that they may pass their wariness on to their progeny, creating more and more ‘shy’ animals. And that five per cent of survivors is very expensive: while ordinary pest suppression costs around $20–$30 a hectare, eradication can be an order of magnitude more expensive.

Manaaki Whenua’s Dr Patrick Garvey has been thinking about what makes a survivor. Things like, might they have predictable behavioural characteristics? If so, how can we manipulate those using innovative cues to overcome their caution?

Garvey identified three such cues: the attractiveness of baits or lures, the ‘fearfulness’ of the trap, and the surrounding environment.

“Manipulating any one of these will increase the likelihood that an animal interacts with a device,” he told the NZ Herald recently.

He suggests switching to lures based on predator scent, rather than food, to attract some wary stoats and weasels, while traps or detection devices might be made less threatening by using more natural-looking materials or setting them below ground.

Holding the line

Eradicating those last few predators from big areas will be challenge enough and that’s just the first part, as preventing them from re-invading is a whole other thing.

Predator-proof fences work, but they’re not practicable, or affordable, to able to be used at the kind of landscape scale that Predator Free requires.

Burwood Predator Proof Fence
📷: Benhi Dixon, DOC

That means using physical features as barriers instead. To date, people have looked to high mountains, or fast-flowing rivers, to turn back predators, but our idea of a barrier is changing all the time.

Wellington’s Miramar peninsula is the site of an intensive urban predator eradication project. Possums have already been removed from the peninsula, and rats are now down to very low numbers. Miramar residents are depending on an entirely artificial barrier to keep them from coming back — Wellington Airport’s main runway.

It turns out that any open ground might provide a suitable deterrent, so that tracts of open farmland are now also being considered as moats to defend cleared areas.

Research will start this year to look at predator eradication on farmland and if the placement of traps and bait stations could detect and remove every predator that reinvades — creating a barrier to movement — or a new type of fence.

One glance at a map of New Zealand shows an abundance of large areas that could be cleared of predators if surrounding farmland was utilised as a barrier.

Species like kakariki karaka/ orange fronted parakeet are at risk due to predators such as mustelids and rats
📷: Sabine Bernert

Trapping too

Virtual boundaries (lines of strategically-laid trapping and surveillance devices) are also holding promise.

Predator control company Zero Invasive Predators (ZIP), assisted by funding from us, NEXT Foundations and Predator Free 2050 Limited, is developing an eradication methodology they’re calling Remove and Protect

While the Remove part still relies largely on aerial toxins, the Protect part will keep predators out of cleared areas of tough terrain where fences are out of the question. What’s more, a virtual barrier can be easily shifted as cleared areas expand.

ZIP has been trialling Remove and Protect in 12,000 hectares of Westland tiger country, the rugged Perth Valley.

Perth River
📷: Jack Mace, DOC

It’s bounded by turbulent rivers — the Perth to the north and the Whataroa to the south, which rats, stoats and possums are reluctant to cross, but the riverbanks are also lined with sophisticated AI detection devices, automatic lure dispensers and traps, all connected to a low frequency radio network.

All 12,000 hectares, once home to an estimated 15,000 possums, were recently declared possum free after none had shown up on any of 143 lured trail cameras for more than 14,000 detection nights, nor in the 700 traps dotting the valley.

Just the same, re-invasion is, for now, a fact of life — stoats re-appeared in the valley in January after months of absence following a 1080 drop. But low numbers of invaders may not be the threat we once imagined.

The CEO of ZIP, Al Bramley, recently told Radio NZ: “The important thing is detecting intruders quickly, and not allowing large populations to establish.

“For possums and stoats, this might be as long as a year, so there’s no need to panic. Meanwhile, we’re continually snuffing them out at the edges, and maintaining predator freedom at the core.”

As our understanding of animal behaviour — what makes an individual skirt around a trap or decide to strike out across a river — improves, Remove and Protect will get easier with time.

Thanks for reading. The Predator Free movement is really important work and it’s going to take a team effort to make it work.

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

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