Predator-free New Zealand: No fences allowed video


Eliminating predators from offshore islands is well understood. Researchers have now turned to peninsulas as the next step to ridding NZ of rats, possums and stoats by 2050. WILL HARVIE reports.

"We wanted it to be real," says Al Bramley as we examine the forbidding 400 metre heights of Bottle Rock Peninsula from a water taxi.

The next day on the peninsula he doesn't have to expand on "real". Rain pounds down. It's the kind of storm that defeats all wet weather gear. Water worms down the back of the neck, seeps up pants and soaks into boots. Those wearing rubber rain gear are soaked by their own sweat.

This Marlborough Sounds terrain is tough. The Queen Charlotte Walkway, which crosses the neck of Bottle Rock, is straightforward if slippery in the deluge. But leave the track and whack a few metres into the bush and you're soon scrambling over dead trees, clambering in and out of gullies and wildly grasping thin bushes for support on sodden moss and leaf clutter.

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Zip staff establish a establish a new experimental trap line for possums in wet conditions.
Will Harvie

Zip staff establish a establish a new experimental trap line for possums in wet conditions.

We find a team of four, all wearing crampons on their boots for traction. They're staff with Zero Invasive Predators (Zip), a non-profit that's secured serious money from the Department of Conservation and leading philanthropists to research how to rid New Zealand of rats, possums and stoats.

Remember in July when John Key and conservation minister Maggie Barry announced plans to make NZ predator free by 2050? Barry was clear that "not all the technology to make New Zealand predator free yet exists". Future scientific breakthroughs are needed.

Some of the people Zip now employs have been working on those breakthroughs since 2013, three years before the Government's announcement. They've made progress and every week are trialling new techniques and technologies to find and kill those predators.

Zip's opening proposition is that we're good at ridding small islands of predators. We've been doing it for 50 years and Doc manages over 100 mostly small islands. We're among the world leaders in the field.

The next step is peninsulas. They are helpfully surrounded by water on three sides and connected to a mainland by a thin neck of land. Can we make a peninsula predator free?

Killing all pests on a peninsula is fairly straightforward, just like an island – 1080 and other poisons, traps and vigilance.

Keeping a peninsula predator free is not. Pests will reinvade almost immediately. So the obvious thing is to fence a peninsula at the neck. Job done.

But fences will not make NZ predator-free by 2050. "We know some communities don't like to be fenced," says Zip's chief executive officer Al Bramley. Fences are also expensive and not especially robust. They need maintenance. Plus you can't fence a road or railway line or bridge. Nor towns and cities.

Bottle Rock Peninsula in  Marlborough Sounds on a good day. The Queen Charlotte Walkway crosses the saddle on the left. ...

Bottle Rock Peninsula in Marlborough Sounds on a good day. The Queen Charlotte Walkway crosses the saddle on the left. Ship Cove, where Captain Cook landed in 1770, is behind.

And using fences wouldn't advance human knowledge.

So Zip's self challenge is keep a peninsula predator free without a fence. How do you do that?

With a "virtual barrier". Lines of traps that kill or capture almost every last rat, possum and stoat that enters the barrier zone.

Yes, a few will get through and stoats have been documented to swim 5 kilometres, rats up to 1km. So there needs to be something behind the barrier to detect invaders and alert rangers there's a problem.

Zip calls this approach Remove and Protect and I've travelled to Bottle Rock, 45 minutes by boat from Picton, to see it in action.

From the water taxi we peak around the north side of the peninsula and into Meretoto​/Ship Cove. This is where Captain Cook took shelter in 1770 and returned several times. It's probably one of the first places European rats landed on Aotearoa. Today it's beside ground zero for their eradication.

There are other ground zeroes around New Zealand, including a National Science Challenge, pest work at every university in the country, private and community-based initiative all over the place.

Zip's role is to spend $20 million on its research over 10 years and it expects to have a good crack at some of those future scientific breakthroughs.

So, how does a virtual barrier work?

We've got experiments stacked up, says Zero Invasive Predators chief executive Al Bramley at a field lab on Bottle Rock ...
Will Harvie

We've got experiments stacked up, says Zero Invasive Predators chief executive Al Bramley at a field lab on Bottle Rock Peninsula, Marlborough Sounds.

Removing pests from Bottle Rock was accomplished, not easily, with standard methods of poison and traps. Zip rangers estimate there were 4000-5000 rats, 3000 possums and perhaps 12 stoats.

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While that was underway, Zip established its virtual barrier, a 600m-wide, 2km-long strip that was filled with six parallel trap lines. Bramley talks about the barrier being "intensively" trapped. The conservation engineer means it. At the moment some rat traps are 5m apart.

Behind the barrier, Zip cut parallel tracks 100m apart. These are D lines and filled mostly with detection devices that tell rangers if any predators have leaked through the barrier. All told, Zip cut 60km of tracks across Bottle Rock.

This infrastructure is necessary so that Zip can run hundreds of experiments on detecting and killing rats, possums and, starting more recently, stoats.

On that super wet day last week, for example, Zip staffers were installing a new virtual barrier trap line for possums. Some of this technology was previously tested at Bottle Rock; other parts were being rolled out in new experiments.

First the traps were screwed to a tree about 1m above the ground. This stops ground birds, especially weka, from being caught.

Second, Zip staffers were installing a wooden ramp up to the trap. This helps the Australian marsupials climb to the trap and Zip staffers have previously spent time figuring out what angle best encourages possums while defeating weka.

But Zip isn't sure the ramps are needed. Possums are curious creatures. They spot something out of the ordinary, they investigate. It might be that possums are investigating the ramps because they are novel.

So Zip is installing some possums traps in trees without ramps and will compare the catch rate. Whatever works best they'll go with.

Bramley calls this process "change, learn, change, learn" and it happens fast with Zip. If something isn't producing results within a few months, it's modified or dropped.

For example, possums are largely nocturnal. So Zip is trialling little glow-in-the-dark pieces of plastic that are screwed to the tree above the trap. The size and shape of this plastic is open to research. Some are flat, two-dimensional patches. Others are folded, three-dimensional shapes that might catch a possum's attention from an angle.

Zip is also trialling flashing LED lights. Their twinkle might be better than luminescent plastic and the batteries last years. Zip guys like their gadgets.

Rats were equipped with trackers so their behaviour in the wild could be investigated.
Zero Invasive Predators

Rats were equipped with trackers so their behaviour in the wild could be investigated.

Meanwhile the trap is housed on a small platform. The prototypes of these were cut from overseas hardwood but that's expensive and unsustainable. So Zip designed a moulded platform and a beta version of these were being installed in the wet the other day.

OK, a ramp or luminescent thing has lured a possum up to the trap platform. Now what? Well, squeamishly, the trap is not lethal. It's a leg-hold trap attached to a 1m chain. Hopefully the possum steps on the trap with a hind leg, falls to ground and is held by the chain.

Under NZ law, that trap has to be cleared within 12 hours of sunrise. So a Zip staffer has to find the trapped possum and kill it. Because possums get caught at night, this is usually the first task in the morning.

"It's good to have a site which is experimental," says predator ecologist Dr Helen Nathan.
Will Harvie

"It's good to have a site which is experimental," says predator ecologist Dr Helen Nathan.

"We'd love to have possum-kill traps but we've measured this now and they're half as effective as leg-hold traps," says Bramley. "We have to intercept every possum."

As compensation, Zip has come up with a clever innovation. About 1000 traps at Bottle Rock are equipped with electronic beacons that record when a trap has triggered. The beacons communicate with a nearby electronic box which bounces the data off a satellite and into Zip's computers.

It sends the data by text to Zip's duty officers at Bottle Rock.

They know the GPS location of every trap and move smartly to dispatch the possum. The rangers also capture data about the animal – sex, age, condition and the like. Sometimes the animal is taken away for dissection. This data is collected for rats and stoats as well. There is less urgency with these animals because they are killed by the traps that target them specifically.

It is all analysed by a full-time statistician at Zip's HQ in Wellington and he fuels innovation. Do rat traps spaced at 10m apart catch more than traps spaced at 20m? About 20 per cent more. OK, what about rat traps spaced at 5m? "It's too early to tell," says Zip's predator ecologist Dr Helen Nathan.

Do rats prefer cheap Chinese peanut butter or expensive New Zealand peanut butter? (The Kiwi stuff.) Does cheese measure up to Nutella? Do stoats go for rabbit meat? How should it be presented?

Social lures may show more promise than food lures. With predators it means, for example, using the fabric rats sleep in at Zip's breeding facility in Lincoln. Small amounts go into traps and the smell attracts other rats.

It turns out that male rat bedding is more effective than female bedding at luring rats of either sex. "We can't figure that out," says Bramley.

Researcher are also looking at creating predator pheromones – chemicals produced by mammals that affect behaviour. Another experiment placed tiny speakers in traps to broadcast sound recordings taken of a family nest of rats. Yes, they've run an experiment using a drone.

"We've got things we want to try stacked up," says Bramley."Is there an effect? Yes. Let's see how powerful it is."

"It's good to have a site which is experimental," says Nathan. "It gives us the opportunity to play around with things."

Zip's 14 staff expect to have finished experimenting at Bottle Rock by 2018-19. The virtual barrier and remove-and-protect systems will work well enough to take them elsewhere. Bottle Rock is 400ha and Zip is already looking for a 4000ha site.

This could be followed by 20,000ha and then 50,000ha sites. To put that in perspective, Banks Peninsula is about 115,000ha.

In a recent presentation to communities, Bramley mentioned that peninsulas were strong contenders. He preferred a site that "lends itself to progression" – establishing a virtual barrier near the tip of a peninsula, say, and sweeping down the length in steps.

But even at the next level, 4000ha, Zip needs community participation. Nathan calls it "social buy-in". In short, Zip can't do the job itself. It will need a "consortium" of stakeholders – the local community, interested landowners, maybe a trust to employ "rat patrols" to clear traps and maintain the barrier, Bramley says.

Zip will be alongside those efforts, advising and watching and learning. Some of those scale-ups will need to be in different environments than Bottle Rock, so Zip can adapt its technologies and techniques to different landscapes and ecologies.

But Zip will never be big enough to rid NZ of rats, possums and stoats. The Department of Conservation won't ever tackle the challenge by itself, Bramley says, as does the Government. It's been estimated the goal will cost many billions.

Zip is one of those public-private partnerships designed to spread the funding burden.

Zip got $10m from the Next Foundation, a charity endowed by Annette and Neal Plowman to fund "game-changing large-scale transformational environmental initiatives". Doc added $5m while Gareth and Sam Morgan between them donate $300,000 a year. Six dairy companies later contributed $3m, which was used to create a research facility at Lincoln.

Bramley reckons he has enough money for now and won't be asking for support from the Government's Predator Free NZ 2050 initiative announced in July, at least for now.

But he's aboard with the intention. "If you're not in the game, it almost seems impossible," he says. It's not, he says.

"It won't be easy but it's feasible ... technically we'll get there," says Nathan.

"A lot of people see us as in the short game, trying to do stuff quickly and not doing the blue sky research."

Rat and stoat traps are spaced 5m apart along the Queen Charlotte Walkway. Note the electronic beacon on the left trap.
Will Harvie

Rat and stoat traps are spaced 5m apart along the Queen Charlotte Walkway. Note the electronic beacon on the left trap.

Yes genetic modification or something similar might be needed to achieve predator-free status. That's not Zip's field. But there will be significant legislative and social challenges to overcome before that stuff is rolled out, he notes.

In the meantime, Zip will keep experimenting, keep changing and learning. The folks at Bottle Rock will endure more wet days.

"We're not anti-fence," Bramley says. They'll have a place, perhaps running alongside railways or waterways, surrounding whole farms.

Field ranger and animal behaviour technician Tim Sjoberg, left, and Al Bramley examine an experimental "pit trap" for stoats.
Will Harvie

Field ranger and animal behaviour technician Tim Sjoberg, left, and Al Bramley examine an experimental "pit trap" for stoats.

Barriers will have their place too. "No-one is saying the barrier won't leak. You just have to get the leakage rate so low that you manage incursions."

In time, the nation's borders might become the barriers. Rats landing from ships will be treated as they are already, as biosecurity hazards that are trapped at ports.

And that's Zip's goal: "Not a rat, not a stoat, not a possum," says Nathan.


It's estimated these three introduced mammals eat 25 million birds and eggs in New Zealand every year. They are responsible for about 85 per cent of native bird loss. They also compete with native birds, lizards and invertebrates for food and resources.

Rats eat almost everything, including bird eggs. Possums eat birds and destroy forest canopies. They also spread bovine tuberculosis to deer and cattle, which is why dairy companies have funded Zip.

Stoats have caused the extinction of several native bird species and caused the decline of others. They can kill kiwi birds up to about 1 kg in weight.

Pet dogs and cats are not on the predator list, although feral animals in rural areas are fair game. Zip has captured several feral cats at Bottle Rock.

Mice are too hard to eradicate, says Zip chief executive Al Bramley. Pigs, goats and deer are introduced pests but don't contribute much to native bird decline.


It's about the size of a spa pool, but could one day be significant tool for killing stoats. It's a round wooden structure with a hood around the inside rim that prevent stoats from escaping.

The pit was initially built to test how high a fence had to be to deter stoats (800mm). But researchers found that stoats at Zip's facility in Lincoln, Canterbury, returned to the pit after they were released. Lured by food, they jumped back in and couldn't get out.

That germinated an idea: Give stoats a route out – a tunnel – that contains a trap. Lured by food and then a tunnel, they'll walk to their deaths. It was promising enough that Zip dropped a pit by helicopter at Bottle Rock to see if it works in the real world.

Stoats have large, overlapping ranges so one pit could service a large area as many stoats would eventually find the pit.

"When we started, we didn't know what we'd have to engineer," says Zip chief executive Al Bramley.

 - Stuff


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