New Zealand wants to kill millions of invasive predators to save these fragile birds
It’s been called “the most ambitious conservation project attempted anywhere in the world”—will it actually work?
The trail was steep, overgrown, and slippery from rain. I had to grip tree trunks and clumps of leaves to keep from sliding down the mountainside. It was springtime, and in this forest reserve in northern New Zealand, chicks were hatching. My friend and I were part of a volunteer effort to help protect them from a ruthless invasive predator—and packed accordingly. Our backpacks contained bags of orange-scented rat poison.
Except our target wasn’t rats at all. We were after stoats, small carnivorous mammals introduced to New Zealand in the 1870s that are especially deadly to native birds. These animals are lean and lithe with kitten-like faces. They’d be almost adorable, if they weren’t such devastating killers. A stoat can climb a 60-foot tree to take down a fully grown pigeon, grappling the bird off its perch before forcing it onto the ground below. Once the bird is subdued, the stoat typically sinks a pair of long canines into the back of its head to eat its brain, followed by bodily organs and eventually the remaining meat. Stoats were introduced to control rabbits but became adept at killing ground-dwelling birds like our iconic bird, the kiwi.
The challenge with stoats is they are wary of traps and toxins, so we were deploying a work-around by stocking dozens of small bait stations—molded plastic boxes screwed into the base of trees—with toxic pellets that rats find irresistible. Rats are another invasive predator, but more important for this gambit, stoats will also prey on them. If you can poison a rat heavily enough, then any stoat that eats it will probably die too. That way, you can rid the forest of two predators in a single stroke.
Dozens of native birds now exist only in taxidermy form, like these at the Museum of New Zealand Te Papa Tongarewa. The features seen on these specimens, from fluffy feathered bodies to sharp beaks, evolved over millions of years. Less than 1,000 years of human habitation wiped them out.
Such logic may sound heartless, but there’s a much larger mission at stake for my entire country: Stoats, rats, and other non-native mammalian pests are destroying the unique ecology of New Zealand. Over the centuries since these animals were introduced, many of our indigenous species have been wiped out because they aren’t adapted to defend themselves against ground-hunting mammals. We now find ourselves at a turning point, with a chance to accelerate steps to undo generations of ecological harm. Although the ethical quandaries around directly intervening remain complex, the strategies and technology for killing predators continue to improve.
(These predators are nature's pest control.)
Life on the land that came to be called Aotearoa, the Maori-language name for the New Zealand archipelago, evolved for 80 million years in the complete absence of terrestrial mammals other than a few bat species. Then, in the blink of an evolutionary eye, that changed when humans started arriving around 750 years ago, bringing with them—albeit sometimes inadvertently—wave after wave of new threats.
Today the most common invasive predators have hunted more than 55 bird species to extinction, including some of the only flightless songbirds ever to have existed, two kinds of flightless geese, and a remarkable bird called the huia, one of a family of wattlebirds found only in New Zealand. This bird, highly sacred to Maori, had a most unusual feature: Male and female birds had dramatically different bills. Four-fifths of the country’s remaining endemic birds, including kiwis, are at risk of the same fate. Ninety-four percent of native reptiles are similarly threatened, as are two of our three native species of frog.
To counteract the destruction, New Zealand officials have mounted an offensive for humans to hunt the hunters into total elimination. Almost a decade ago, in 2016, then New Zealand prime minister John Key announced the government’s seemingly audacious goal of completely eradicating major predator species by 2050. The seven invaders specifically targeted are three different types of rats, plus stoats, ferrets, weasels, and possums.
Key dubbed this “the most ambitious conservation project attempted anywhere in the world.” The late New Zealand physicist Sir Paul Callaghan, one of the first to articulate the predator-free vision, likened the difficulty of achieving that goal to creating an Apollo program—our country’s moon shot. The effort has been estimated to cost upwards of six billion dollars.
New Zealand has a land area of 100,000 square miles, with invasive predators spread across not just mountains and forests but also glaciers, dunelands, wetlands, and hundreds of urban areas. Any solutions would need to operate effectively on all of those frontiers.
(What’s a ‘dark sky nation’ and why does New Zealand want to become one?)
Nine years after the predator-free campaign launched, however, conservationists agree that existing control strategies—even deploying poison to kill two predators at once and other techniques developed in recent decades—won’t get us to zero by 2050 or possibly at all. The geographical scale is too great, the available resources too thin, the collateral damage too difficult to manage.
But achieving any moon shot has always required rethinking just about everything. Right now, that’s what ecologists, biologists, trapmakers, ethicists, and engineers are doing—combining their strengths to learn from the past while accelerating the pace of innovation. Despite the obstacles, the progress they’re making has them imagining a hopeful new future: birds safe, predators gone.
It has been estimated that 95 percent of kiwis that hatch in areas where stoats are active do not live to adulthood.
No creature captures the predicament of New Zealand’s native animals evolving in isolation better than the kiwi. The epitome of beloved weirdness and vulnerability, kiwis are about the size of a chicken and have attributes similar to the mammals that were largely absent during New Zealand’s evolutionary history. There are five species. All are nocturnal and flightless with catlike whiskers and furlike shaggy feathers. They even have marrow in their leg bones—all unbirdlike features.
(How New Zealand's glaciers shaped the origin of the kiwi bird.)
To encounter a kiwi in the wild, watching it probe the leafy humus, pushing its five-inch bill almost to the hilt as it hunts for grubs, is to be transported to an arcadian epoch when birds had no need to escape ground-dwelling threats. But that protective environment changed abruptly when humans arrived from eastern Polynesia with the first recorded invasive predator, the kiore rat, which may have been carried on their voyaging canoes as a food source. The danger grew with the arrival of Europeans, who introduced black and brown rats that likely traveled with them as stowaways on ships during the 18th and 19th centuries.
More intentional animal introductions also went awry. Colonial settlers unleashed a deadly triumvirate of ferrets, weasels, and, of course, stoats, in an ill-conceived effort to keep rabbits, which themselves were introduced for food and sport, in check. The proposed control agents barely dented the rabbit numbers, turning their attention to birds and other fauna, which were much easier to catch and had no natural defenses against them. Then, in an attempt to establish a fur industry, colonial New Zealanders imported the Australian brushtail possum, which is a bit larger than its American cousin, with a furry tail and luxuriant pelt. These omnivorous eaters quickly spread through the country’s forests. By the 1980s, more than 50 million possums were estimated to be in the wild, consuming 23,000 tons of vegetation every night, along with birds and their eggs, snails, and other invertebrates.
The cumulative damage inflicted by these animals is almost beyond comprehension. At least 25 million chicks and eggs of native birds are believed to be consumed by such predators each year. It has been estimated that 95 percent of kiwis that hatch in areas where stoats are active do not live to adulthood. “Every New Zealand habitat is under siege,” says Colin Meurk, a landscape ecologist at the University of Canterbury.
The initial attempt to eradicate predators began 65 years ago on many of the country’s small offshore islands. The techniques and devices used were rudimentary: hardware-store snap traps for rodents; bigger, more powerful versions for stoats; toxic baits dropped from low-flying aircraft to blanket an entire island with rodenticide.
But the effort worked. More than 300 New Zealand islands are now predator free and have become sanctuaries for vulnerable creatures such as the tuatara, a lizard-like reptile that’s evolved little since the age of dinosaurs, and the owl-faced kakapo, the world’s only flightless parrot. The elegant tieke, or North Island saddleback, which is named for a chestnut blaze of feathers across its jet-black plumage, once survived on only one predator-free island. It has since been reintroduced to others as those areas have become safe to inhabit.
Next-generation AI-powered traps will soon join this tool kit of toxins, bait stations, and automated killing machines to propel New Zealand to its 2050 goal.
(How New Zealand saved a flightless parrot from extinction.)
On the mainland, gains have been slower and hard-won. In Miramar, a four-square-mile peninsula in the country’s capital city, Wellington, it took workers for Predator Free Wellington four years to fully rid the area of black and brown rats, stoats, and weasels. Doing so required installing more than 11,000 bait stations and traps in residents’ yards, schools, shopping centers, and even the studios where sets for The Lord of the Rings were constructed. These had to be checked weekly for at least six months before project staff began the extended process of locating any animals that had evaded traps and toxins. At least a thousand Miramar households formed their own volunteer network to help out.
Through careful management, key predators have also been removed from a 350-square-mile swath of wilderness in the country’s mountainous southwest—proof that eradication is possible in both urban and backcountry regions. But all told, the area cleared so far is still less than half a percent of the whole country.
Tens of thousands of New Zealanders have proved willing to engage in this effort. Many schools teach students how to humanely trap and kill predators as part of a conservation curriculum. Now eradication experts want to accelerate progress by increasing the impact of these volunteers. Dan Tompkins, science director of Predator Free 2050 Limited, a company that allocates government funding toward future innovations, says one of the top priorities is to dramatically reduce the time spent servicing killing devices in the field.
Self-resetting traps with dispensers to automatically bait them are already doing that. The devices can operate autonomously for months while sharing their catch status and other data, giving project staff a continuous update on predator numbers and activity.
One popular variety has the trap mechanism housed in a wire-mesh cage that is screwed to a tree at shoulder height to keep it out of reach of curious ground birds, such as kiwis. A wooden ramp leads predators up to the device, which they enter from below, lured by the promise of food. (The specially formulated bait, appealing to both rodents and possums, is a flavored mayonnaise.) When the animal crosses a light beam, the trap triggers. A kill bar crushes the skulls of rats and mice and strangles the much larger possum. Once it has been triggered, a motor rebaits and resets the trap, rewinding the kill mechanism. The carcass then drops out of the trap enclosure to the ground.
Our self-resetting traps have been catching two to six possums per night, and we might not need to check the trap more than once every six months.Paul Kavanagh, project director
These traps are being deployed across the country. In the Southern Lakes region of New Zealand’s South Island, Paul Kavanagh, the project director for a consortium that supports over a hundred volunteer groups and conservation-minded organizations, estimates that self-resetting traps are 49 times more effective than traditional devices. “Our self-resetting traps have been catching two to six possums per night, and we might not need to check the trap more than once every six months,” he told me at a project field site in the hills behind Queenstown.
In contrast, a single-set trap might make one kill and then be out of service for a month until a volunteer comes to reset it. Other lower-tech devices require even more work. Leghold traps, commonly used in the fur trade but also sometimes in pest control, don’t kill animals outright. New Zealand law requires they be checked every 12 hours so the animal can be dispatched without undue suffering. Collectively, the 400 self-resetting traps at Kavanagh’s field sites dispatched more than 7,200 pests in 12 months. “It’s game-changing technology,” he said. “We used to say you can’t trap your way to predator elimination. These traps are challenging that idea.”
Until now, traps have also needed to be placed inside boxes or structures with openings just wide enough to admit the target predator but prevent nontarget species from being snared accidentally. The problem is, many predators are trap shy—disinclined to enter the confines of a box or other housing, despite the temptation of a tasty treat.
(How predators get past the trickiest of defenses.)
That’s changing with artificial intelligence recognition, which allows for a trap that is completely open. These traps, expected to debut this year, will trigger only when the target predator approaches them and an AI-powered camera confirms the identity of the species. In addition, whereas traditional traps require the target animal to push, pull, or stand on a trigger to activate them, AI traps do not demand that level of interaction. They ensure an instant kill with few near misses and, importantly, create less collateral damage.
If we don’t do anything, we’re not going to be able to experience the joy of birdsong.Chelsea Price
With the loss of each species, we lose part of our national and individual identity.Steven Cox
While some inventors focus on trap technology, others use their understanding of predator behavior to advantage. One product that’s close to being released commercially is the Spitfire. It’s designed to turn the grooming impulse of furry animals into a fatal last act.
(What are animals saying? AI may help decode their languages.)
The device could use peanut butter to attract predators. To reach it, an animal must stand on a platform, which records its weight. This then triggers an infrared beam to assess height, accurately determining whether this is a desired target—all within a fraction of a second. Once a positive identification is made, the device sprays toxin onto the animal’s belly, prompting the critter to groom and, in so doing, ingest the toxin. Spitfires can deliver up to a hundred lethal doses and be left in the field unattended for a year.
One development that excites Tompkins is the impending commercial release of the world’s first rat-selective toxin, a chemical called norbormide. It was discovered by accident in the 1960s but fell out of use because of inconsistent effectiveness and the emergence of second-generation anticoagulants. Now it shows promise in reducing the collateral damage of eradication efforts. “A rat toxin that puts no other species at risk is a game changer,” he says.
For example, the rat toxin I carried through the forest could accidentally poison a range of birds and animals, including dogs, which might scavenge a poisoned carcass. A rat-specific toxin could be deployed to remove the last holdouts in a rodent population and prevent reinvasion once an area has been cleared to ensure the removal is permanent.
New Zealand is now poised to automate the mass killing of animals on an unprecedented scale. But some animal rights experts argue that the predator eradication community hasn’t always addressed the obvious ethical implications.
“I’m not opposed to the principles of Predator Free 2050,” says Ngaio Beausoleil, co-director of the Animal Welfare Science and Bioethics Centre at New Zealand’s Massey University. “But if you’re going to undertake something that has potential impacts for millions of sentient animals, then there’s an ethical obligation to do the best you can for them.”
The eradication effort—at least, as conducted so far—hasn’t met the correct standard of compassion, critics argue. “The campaign in New Zealand to exterminate all non-native animals … relies on the use of poisons which are known to cause intense suffering and agonizing deaths,” conservationist Jane Goodall stated in her own ethical review of the eradication programs. “As I read more and more about this plan, I became increasingly concerned.”
For now, despite their welfare issues, toxins remain indispensable to the predator-free mission. But as James Russell, an ecologist and National Geographic Explorer who works to restore endangered populations, explained to me, there are two kinds of animal welfare to consider—that of the predator and that of the prey. The harm that predators inflict on native species far exceeds the harm we inflict in managing them, he argues. “The presence of mammalian predators in Aotearoa is an historical environmental injustice,” Russell said. “Just as we try to correct historical social injustices, I believe we should try to correct historical environmental injustices.”
On a late May day I was helping Russell catch and band gray-faced petrels, one of the few burrowing seabirds that still nest on the mainland. A petrel may traverse thousands of miles of ocean in its lifetime. To hold one in your hands reinforces this feeling of environmental responsibility.
Not acting is ethically fraught too. “Doing nothing about predators gives them a license to kill,” says Brent Beaven, who manages the Predator Free 2050 project for the government’s Department of Conservation. “You make a choice, and it’s an active choice either way. Indigenous species or animals that don’t belong here—which one will it be? Either way you’re condemning animals to death.”
The Maori have another perspective on the issue. For them the natural world—te taiao—is literal kin. In the Maori worldview, human and nonhuman are woven together like fibers in a traditional cloak. Break any individual thread, and the entire garment starts to unravel.
On Aotea (or in Western terms, Great Barrier), an island off the coast of Auckland, Maori are taking the lead in removing predators, so that the unraveling can be halted and the cloak restored. They call the project Tu Mai Taonga—Let the treasured ones stand strong. “They were here before us,” says Marilyn Davies-Stephens, one of the project’s leaders, of the indigenous species. “They’re our tupuna”—the Maori term for ancestors. “A wrong has been done to our tupuna. We need to turn it around.”
(The Māori saved their language from extinction. Here’s how.)
There is escalating momentum now. Sixty years ago, when the first New Zealand island was cleared of rats—a tiny speck of land the size of four football fields—the attempt had seemed futile, and the result miraculous. Each decade since, the size of islands cleared of predators has increased by an order of magnitude. New Zealand technologies and expertise have been employed for island eradications around the world. Success can be measured in other powerful ways. When I was a child, a kiwi egg used to hang on a nail in the family beach house in the Bay of Islands. The shell was huge, almost five inches from end to end. Kiwis lay the largest eggs relative to body size of any bird—up to a fifth of the mother’s weight. I marveled at that egg but never saw the bird. By then, stoat predation had rendered kiwis in the north a rarity. But our efforts have changed that. Now in the bay I hear them every night.
A New Zealand native and a National Geographic contributor since 2000, Kennedy Warne has specialized in telling stories about natural history and biodiversity.
An Explorer for six years, Robin Hammond has traveled the world as a photojournalist. This story took him back to his native country for a project that, he says, became “one of the highlights of my career.”
