The hapless hedgehog recently swept away in an avalanche near Mt Cook serves as a strange but true example of the lengths field workers are going to, on what is likely the country’s most ambitious pest control project yet.
Covering more than 300,000ha of the Southern Alps and surrounds, the exemplar project is inching New Zealand closer to having its first ever pest-free national park.
Aside from early Māori moving through the valleys and a handful of hardy European explorers, few people have ever seen this alpine wilderness in its natural state.
Most have no concept of what the normal populations of New Zealand’s quirky native alpine species should and would be, without predators around.
Aoraki Mt Cook National Park contains landscapes that fuel our international tourism industry and contribute to the identity of the nation…big skies, turquoise lakes and tussock-covered valleys which disappear into a haze of alpine mountain ranges going on and on, as far as the eye can see.
“This is a massively iconic landscape. People from all over the world come to visit this place, it gets a million visitors a year,” Te Manahuna Aoraki Project (TMAP) manager Simone Smits says. “The real opportunity here is restoring biodiversity in a place where people get to readily see and encounter it.”
For the past four years, with growing intensity, TMAP has been targeting seven plant and eight animal pests plus a few winged invaders on the side. The activity currently centres around the catchments of Lake Pukaki and Tekapo in the Mackenzie Basin.
The full cost of the project was not available by deadline but TMAP confirmed $4.3M has been spent so far on pest elimination in the alpine area.
The aim is to simultaneously remove the swag of notorious pests – feral cats, hedgehogs, stoats, ferrets, rabbits, hares, Norway rats and possums – that have been decimating native species in the area for over a century.
“The number one thing that is threating biodiversity is predation,” Smits says. “The predator populations are driven by their predominant food source and that’s hares above 1000m and rabbits below 1000m.”
Canada geese and black-backed gulls are also targets and while the latter are a native species, agricultural food sources have allowed their populations to build up to unnatural and destructive levels.
Weed control came first and now the rowan, broom, lupin, gorse, cotoneaster, flowering cherry and willow have been reduced to levels where landowners or managers can take back over. Wilding pines, which are a huge headache on their own in this area, are not on the list as they are managed by a separate organisation.
Over the past four years, a 50,000 hectare alpine area near Mt Cook has been a focus. It makes up 70 percent of the national park and borders the 100,000ha South Westland block where pest control organisation ZIP have already spent five years and $50m eliminating predators.
In this alpine zone, high above the bush line, scree wētā freeze solid all winter then thaw out in spring and get on with their lives. They share the mountainside with lots of uniquely adapted creatures including tiny, tail-less rock wrens who prefer to scurry about on their outsized legs rather than flying. These tenacious little birds line their nests with feathers amongst the rocks, laying eggs the size of 10-cent pieces.
The wētā, eggs, chicks and adult wrens all provide easy protein for the predators wandering these lonely heights – feral cats, hedgehogs, possums and stoats. Kea have also been hunted by these introduced predators in the snowy alps for decades. The ground-nesting birds are fair game and around 60 percent of nests fail due to predators, according to Predator Free 2050(PF2050) data.
The bane of the entire basin is, of course, that steady back-up diet supporting predator survival – hares at altitude and their compatriots on the valley floor, the dreaded rabbit.
TMAP was launched in 2018, bringing together dozens of people from diverse groups. Existing conservation groups came together with the Defence Force, PF2050, farmers, philanthropists, Crown agencies, Ngāi Tahu and regional government. A carefully coordinated collective effort with both private and public funding was the only way results could be achieved in such a challenging environment, Smits says.
ZIP was engaged to do the research and control work, it too being funded by a mix of public and private sources.
Smits says the landscape has natural pest barriers that hinder re-invasion once the animals are eliminated.
“It has a high level of defensibility. It’s surrounded by really strong, high mountain ranges, large hydro-lakes and a hydro-canal. Naturally we get some incursions but the key thing is to make sure it’s very low and we can pick up whatever crosses quickly and remove it before it re-establishes a population.”
Stoats can swim across the deep, swift canals, and land borders, no matter how rugged, were not impenetrable.
Hedgehogs have been found here at altitudes of nearly 2000m. Their main prey is described by the group as “anything they can find” and the description on ZIP’s website is enough to deter most garden-variety hedgehog feeders.
“Hedgehogs may look cute, but they are super-killers, eating chicks, eggs, lizards, skinks, wētā and other rare insects. They are also hosts to many parasites and diseases, various worms, fleas and mites.”
Smits said the group were working hard to prevent hedgehogs spreading into key areas that they hadn’t already invaded. Any found at altitude were an instant target.
“One of our PHD students lost a hedgehog he was tracking into an avalanche – they are surprisingly resilient.”
A network of AI-enabled trail cameras around the vast perimeter are lured to attract pests and programmed to send alerts if something is snapped.
“Every morning when we wake up there’s an email sitting there with what pests were detected, where, overnight.”
Getting the last wary animals is often the hardest job, especially when they are nocturnal,and heat-seeking drones are proving handy tools to help workers quickly hone in on new invaders.
In the valleys these are deployed at night with a shooter on the ground ready to move when a pest is detected. The team’s drone operators have even mastered the art of herding a single rabbit toward the shooter’s location.
Ferrets and detection dogs have been deployed and rabbit fences modified to stop even the slightest of youngsters squeezing through.
The alpine area is broken into three blocks, Smits says, with the first, the Malte Brun Range, now believed to be pest-free.
A mop-up of any hangers-on over the wider area will be done over winter to complete elimination in the remaining blocks, the Liebig and Kirikirikatata/Mt Cook Ranges.
Under the Tomorrow Accord, the government then steps in to protect the gains permanently once elimination is confirmed. This agreement with the philanthropic organisation NEXT gives private funders the assurance the areas will be safeguarded for the future.
All data collected by ZIP is aimed at making the innovations and methods that have been developed for dryland and alpine pest control transferable to similar areas, in an increasingly cost-effective way.
Dryland ecosystems like the Mackenzie Basin cover about 19 percent of New Zealand’s land area, so there’s plenty of scope for expansion.
Dean Nelson, principal ranger for the Department of Conservation’s river recovery project, has seen rabbit populations fluctuate dramatically over the decades. Following each poisoning operation, Nelson says, hungry predators used to feeding on rabbits, would turn to native species to fill the gap.
“Back in the 80s the farmers were doing lots of 1080 operations so you had these boom and bust periods where they’d remove all the rabbits on a big chunk of land and all of a sudden you’ve got all these cats and ferrets and stoats running around with nothing to eat. The impact was on the birds and the lizards and everything else.”
When the Rabbit Hemorrhagic Disease was introduced it steadied the population, but predator numbers quietly climbed in the background.
Nelson has worked for DoC in the area for 21 years but spent another seven years working around Aoraki Mt Cook in the 1980s in the days of the Lands and Survey Department.
He says unlike in areas closer to towns, the feral cats of the Mackenzie Basin didn’t come from dumped kittens but have bred over time from a long line of wild cats, making them much wilier and tougher than your average moggy. Of all the predators, the cats likely established first.
“Possibly cats have been around the longest and interestingly possums were only arriving up at Aoraki Mt Cook in the eighties. Ninety-nine percent of the cats we catch are a genuine feral cat, they’ve been around for a long time.”
A study in the area had found all cats captured were very similar in markings and appearance to the European Wildcat, a truly wild animal that has never been domesticated.
“It’s like they’ve regressed back to their genetic make-up over time.”
He has observed native species decline or disappear completely from some valleys as well as population recoveries – such as with the rare kakī or black stilt – where extensive trapping was done by DoC.
“Some of the valleys where I go tramping now you just don’t see kea anymore. They were always there back when I used to go to those areas.”
Stoats were likely the worst killers of kea and would venture very high into alpine areas if they were hungry enough. Recent recoveries in kea numbers believed to be due to TMAP were fuelling local optimism for better times ahead, Nelson says.
“With the work TMA and ZIP are doing we are starting to see that [kea decline] reversing, we’re starting to perhaps get those numbers back again. What they’ve done is gone a step beyond what we had the resources to do and that’s about trying to actually eliminate the pests.”
Being able to try different methods and use them across large areas was key and those watching on, who knew the area and its challenges, were feeling encouraged.
“I’m optimistic that what they are doing is developing new ways of working that will actually give us the results that we would like to see for Predator Free 2050. It’s exciting from my point of view.”
A huge bonus would be allowing New Zealanders and overseas visitors to see unique native species living naturally in the wild, rather than inside a fenced sanctuary or the like.
“Things like kakī, people will actually be able to go and see them. It’s really important to be able to have all those species accessible to the public. They start to care and start to believe that maybe Predator Free 2050 is a goal that we can achieve.”
Whether or not DoC will have the resources to maintain all areas once the project is completed is an ongoing uncertainty but with AI-enabled traps, better baits and superior night vision equipment already proving effective, Nelson is hopeful.
“It’s really heartening to see the effort that’s going into this and I feel very positive that ultimately we’re going to be able to manage a lot of these pests better than we can now.”
