Zero Invasive Predators (Zip), a research and development entity, has almost eliminated predators from one 12,000-hectare block in the Perth River Valley, South Westland, and is currently watching about half a dozen rats and the same number of possums that survived an aerial 1080 operation, chief executive Al Bramley said.
Zip hopes to drop 1080 on about 10,000ha next door and then defend it for survivors and new incursions – again without using fences.
Both blocks are mountainous and bordered by swift rivers, Bromley said. An international rugby pitch is about 1ha.
Fences are used in wildlife sanctuaries all over the country but they are too expensive and porous to be widely used in the grand project to eliminate predators by 2050, Zip has long maintained.
Instead it favours a model called "remove and protect", under which rats, possums and stoats are eliminated with toxins such as 1080 and traps, and the land defended with detection devices, traps and barriers like rivers and mountains.
It is understood some predators will survive 1080 drops and others will move into the cleared areas. The trick is detecting those animals and responding.
On the Perth River block, it is thought three female rats survived an intense 1080 treatment and Zip is monitoring them – rather than removing them – to see how they respond.
They are currently three isolated pods and Zip researchers want to know if they will seek each other out – and how quickly.
They have "pre-fed" the areas with non-toxic pellets to get the animals used to the bait. If the population explodes, then Zip could respond quickly.
"We're taking the learning opportunity to see how to manage this [and] how quickly do you need do it," Bramley said.
This information could inform how fast Zip or other predator free managers have to respond to an incursion or survival.
Zip is also monitoring the possums for the same reasons. They have been ranging much more widely than is normal – up to 100 times greater, Bramley said.
Last year's aerial 1080 drop completely eliminated stoats in the block but about six have since invaded. Again, they are being monitored and Zip is investigating whether they might be dealt with using poisoned rat or mouse carcasses.
It is thought the initial load of stoats were killed by eating 1080-loaded rat carcasses.
The new block, called the Butler, is more productive than the Perth because it has more lowlands and rimu forests.
But last year's operation in the Perth was done after a modest "mast" event in that part of Westland.
Masts provide large amounts of food and predator populations expand rapidly afterwards.
There won't be a mast this year so clearing the Butler block should be easier, Bramley said.
Zip's model is to progressively expand its protected area using natural boundaries like rivers and mountains.
It hopes to "create an environment on the mainland where, in time, ecological integrity could rival that of predator-free offshore islands".
Zip is funded by the Department of Conservation, the philanthropic Next Foundation and Morgan family funds and foundations.
It is developing a tool box of methods for others in the predator-free effort to use.