Wellington ecologist Jamie Steer is not a fan of the 2050 predator free concept, he says it focuses excessively on recreating the ecosystems of the past when increasingly it's the ecosystems of the future we need to be focusing on.

It must be the only corner of Facebook where parades of triumphant death are considered perfectly acceptable, even laudable. Ship rats, Norways - photo after photo of vermin successfully eliminated by Predator Free NZ traps.

New Zealand's Predator Free vision - which aims to rid the country of possums, rats and mustelids by 2050 - has spurred enthusiasm in back-yard trapping, with communities coming together on Facebook to swap tips on whether gourmet peanut butter or Nutella make better bait.

Decades of predator-control to protect our unique - and uniquely vulnerable - birdlife mean few Kiwis will be shocked by the idea of killing to conserve. But not everyone shares our enthusiasm, sparking debate about our broader approach to conservation.

Visiting American science writer Emma Marris worries that, back home in the United States, kids' first introduction to conservation is often ripping out introduced plants branded as weeds.

"Here it's not even plants - it's animals. I'm curious about how that's going to play out on a mass psychological level, if we're training children that the way you care for Mother Earth is to go kill things."

SUPPLIED American science writer Emma Marris worries about teaching kids to conserve nature by killing things. (File photo)

KILLING THINGS SOFTLY

Let's be clear, in a nation of crazy creatures that evolved in the absence of mammals, killing introduced predators is absolutely necessary. It's just a question of degree.

Predator Free opponent Wayne Linklater - who directs Victoria University's Centre for Biodiversity and Restoration Ecology - argues we don't need to eradicate rats, mustelids and possums everywhere to stop our 900-odd endangered species going extinct. Predator Free 2050, he says, diverts resources, ignores other drivers of extinction such as habitat loss and is an unachievable "science fiction" that risks eroding conservation support when it inevitably fails.

Instead, he advocates an extended national network of predator-free sanctuaries such as Wellington's Zealandia - connected either by habitat corridors or translocation of individual animals, and surrounded by "halos" where pest control allows threatened species to safely spill over beyond the sanctuary fence. Plus research into how different habitats affect reproduction rates. And different approaches in different places, to reflect the fact some Kiwis want to hunt at the weekend, while others want to hike through bush that's not munched by deer.

"We have a complex problem and we're throwing a single simplistic solution at it."

Linklater also has more radical ideas - including transferring populations of our endangered species to predator-free islands controlled by other nations, in case of unexpected diseases or habitat decline triggered by climate change.

SUPPLIED Marris on Mauitaha Island - a sanctuary for culturally significant kiore rats in the Hen and Chickens group. Marris advocates different conservation approaches for different areas, reflecting different cultural values.

Wellington ecologist Jamie Steer argues complete eradication isn't just unnecessary - it's unethical.

Steer's PhD examined attitudes to introduced species and how we have accepted game species such as mallard ducks, deer and trout. He concluded we're unlikely to ever embrace imports like rats in the same way, because we don't consider them useful. However, he contends we have a moral responsibility for the stoats and possums we introduced, just as much as for the kiwi and kakapo which help shape our sense of identity.

"We can't just throw them under the bus and say 'We did like you back in the 1800s, but now it turns out you're not useful to us any more and you contradict things that we find useful. So we're just going to kill you all. But don't worry - we're going to do it nicely'."

MONIQUE FORD/STUFF Wellington ecologist Jamie Steer argues it's unethical to wipe out all introduced predators and wants Kiwis to instead learn to live with - and see the value in - changed ecosystems like this Hutt River spot, where native and introduced species co-exist.

We're also playing favourites, Steer points out. Trout also kill native fish, and deer munch native bird habitats, yet they escape unscathed.

"A lot of dyed-in-the-wool conservationists are ambivalent about eradicating trout - because they like going trout fishing on the weekend as much as they like trapping stoats on weekdays."

Rather than concentrating on eradication, Steer says we should research ways introduced predators and New Zealand's treasured birds, lizards and bugs can co-exist. Some species, like kakapo, will be too vulnerable, and too threatened to risk co-existence. But other natives might survive if managed intensively when they're most vulnerable - nesting or roosting - in the same way Operation Nest Egg rears kiwi in predator-free safety and releases them into the wild once they can fend for themselves.

Apart from the focus on killing, Marris worries a single nationwide conservation approach is risky in an ever-changing environment. More innovative alternatives include Australian projects to expose successive generations of endangered marsupials to low levels of predators, to breed more wary animals; making vomit-inducing cane toad sausages to teach endangered quolls not to eat toxic toads; and light-sensitive nesting boxes that close at night to keep endangered Tasmanian swift parrots safe from nocturnal sugar gliders.

APRIL REESE/SUPPLIED Auckland University conservation ecologist James Russell says while killing for conservation is contentious, doing nothing is not an option.

Auckland University conservation ecologist James Russell agrees telling kids you have to kill wildlife to save wildlife is a message requiring careful handling. But the killing is already happening - it's just at present it's rats doing the killing and birds doing the dying.

"If we don't send that message, are we sending the message it's OK to let humans destroy the environment and let invasive species kill other animals and we don't do anything about it?"

And he doesn't buy Steer's argument that we have equal responsibility to native and introduced animals. It's like getting a pet dog. Yes, you have a responsibility to the dog, but if it starts eating your neighbour's chickens, you also have a responsibility to deal with that.

SUPPLIED Stoats are among three pest groups targeted by Predator Free NZ. The NZ Biodiversity Strategy also singles out goats, deer, and feral cats, but they have not been included.

Andrea Byrom - director of the government research programme Biological Heritage National Science Challenge - says there's nothing new in the ethical conundrum of killing for conservation, but there's no good evidence threatened natives and introduced predators can co-exist.

"The bottom line is in New Zealand if we are going to save particularly a lot of our threatened native fauna - lizards and bats and birds - we're going to have to keep killing stuff. That's just the reality of it."

Byrom is clearly exasperated, accusing Linklater and Steer of "manufacturing dissent" by presenting Predator Free as "eradicate everywhere" extremism, when the country is so far from that goal as to render the argument meaningless. What she sees is a movement mobilising communities, and increasing awareness of the dire straits of our endangered species.

Maybe Predator Free should eventually change its name to Biodiversity Rich NZ to remove the focus on killing pests, Byrom says. She agrees with Linklater that Predator Free 2050 is unachievable with existing technology, but argues we haven't achieved Smokefree NZ yet either, but people still consider that a useful goal. And at a time when even the iconic kea has slid another notch towards extinction - from vulnerable to endangered - anything that galvanises public attitudes and actions should be celebrated, she says.

"At the moment, the pendulum has swung so far to the point where we've got so many species in decline, that I think anything we can do to bring that pendulum back into alignment is the right thing to do."

Marris worries we've become so obsessed with venerating pristine, native nature that we fail to appreciate the beauty all around us.

TRASH OR TREASURE: NATIVE VS INTRODUCED NATURE

There's a beaut spot on the Hutt River - a shady glade of imported willows and native kowhai, with a carpet of flaxes and the striking orange-flowered weed montbretia.

​Native species purists would turn up their noses in disgust. This attitude is one of Steer's - and Emma Marris's - pet peeves.

Marris's book The Rambunctious Garden: Saving Nature in a Post-Wild World railed against the apparent rise of purism in conservation - the idea only virgin, native nature is worthy. Taken to extremes, even natives become pests if they're outside their original natural range.

Marris likes the Zealandia model of bringing a native wilderness experience to the city. Appreciate that, she says, but don't dismiss your backyard ivy and starlings as trash. A reshuffle in an ecosystem's mix of plants can be nature's way of dealing with stress or climate change.

"I think species preservation is ultimately more important than everything being in the right place. Our notion of what the right place is is tied very much to history and to culture. Often the day the first white guy stepped off the boat - that's often what we think everything should look like. And that's not a biological answer; it's not an ecological answer; it's a cultural idea."

ROSS GIBLIN/STUFF Wellington's pohutukawa are technically in the wrong place - the tree's original range was only north of Gisborne.

New Zealand's Biodiversity Strategy pledges to protect introduced species deemed economically, biologically and culturally important. However, New Zealand is not immune from purist zeal. Volunteer "karo busters" spent 10 years ridding Matiu-Somes Island of native karo trees, because they normally grow further north and conservationists feared they would take over. Watch out Wellington pōhutukawa - the glorious red blooms of New Zealand's Christmas tree were originally only found north of Gisborne.

Steer thinks we should stop focusing on the impossible goal of restoring the past and instead adapt for the future. He wants Kiwis to see the value of new ecosystems - the gorse that acts as a nursery for native seedlings; the towering non-native pines that don't fit Zealandia's vision of recreating pre-human New Zealand, but provide safe roosting for its precious native birds.

"We have to figure out what are the things we value the most, that we must prevent from changing, and where are the places that we're going to be able to accept change. Because change is going to happen, whether we like it or not."

SUPPLIED Volunteers dubbed "karo busters" spent 10 years removing the tree from Matiu-Somes Island. Although karo is native, Wellington is outside its original range.

But Russell rejects the idea we shouldn't try to correct our pioneer predecessors' mistakes.

"That argument could be applied equally to 'Look at those crazy humans trying to get CO2 levels back below 200 parts per million - they're just trying to wind back the clock'. It may not be possible and indeed we might have to accept that it's now 400 parts per million, but that doesn't make what we've done right, and it doesn't excuse us of that injustice that we've created."

Byrom also dismisses as "disingenuous" the idea conservationists are trying to return to some "prehistoric nirvana", with no introduced species. It's about finding the right mix of species in the right places, she says.

Marris is anxious not to lecture Kiwis on how to manage their country. Just think about how you see nature, and how you want to protect it, she asks.

"A possum is not a bad person. I think it's important to keep reminding ourselves that even though as the managers of our landscapes we may not want certain species here, that those species themselves are not malicious. They're just doing what they do and it's really us who brought them there. I think there's a little bit of transference going on - we feel guilty about what we've done to our environment, so we end up demonising species that came with us on this voyage of destruction. I see a lot more focus on non-natives than turning huge swaths of landscape over to agricultural production. We tend to want to go after the aliens, not ourselves."

NIKKI MACDONALD/STUFF Trust property manager Mitchell Sedgwick explains what he discovered when student tenants reported strange noises in the ceiling.

THE REINTRODUCTION CONUNDRUM

For six years, biologist Russ Morgan tracked OR4 - the alpha wolf that wandered from Idaho to Oregon, raising the state's first pack since 1947. Morgan watched as the wolf's family grew and it grew old, and he signed its death warrant when it wearied and looked for easy targets - ranchers' cattle.

Marris's moving story about OR4, A Very Old Man For a Wolf, examines the conundrum of the world's current enthusiasm for "rewilding" - reintroducing locally extinct animals.

You've probably seen the Yellowstone video, which shows the park's transformation after wolves returned. As the story goes, the wolves redressed the ecosystem's natural balance, reducing elk numbers, allowing vegetation to flourish and even changing the river's flow. Marris says it's not quite that straight-forward, and neither is reintroduction itself.

"The minute they come out of the shadows, they have to be dealt with. It kind of breaks my heart - it's a lot to ask of them. Yes, we want you to look majestic and wild, when we're out hiking, but we don't want you to come down here and eat our sheep, even though that's what you're genetically programmed to do."

New Zealand has a successful history of species reintroduction, from kokako in Auckland's Waitakere Ranges to saddleback and rowdy kākā in Wellington's Zealandia. But it's not entirely problem-free.

Kākā strip bark to search for sap and insects. From just six birds introduced to Zealandia in 2002, they have squawked and free-wheeled their way to an estimated population of 400. The onslaught is threatening 15-20 grand old conifers in the Botanic Gardens and Wellington City Council has removed about 20 trees because of kākā damage.

While surveys suggest most Wellingtonians love them, new research shows increased concentrations and damage where birdlovers feed the parrots, fuelling potential for neighbourly disputes. Linklater argues they should never have been introduced without a proper impact study.

MAARTEN HOLL/STUFF Kaka have become so numerous in Wellington that Zealandia has stopped intensively monitoring them.

Wellington City Council urban ecologist Daniela Biaggio says tree damage is a small price to pay to support a nationally endangered species.

"What's really cool is North Island kākā are a threatened species but they're actually recovering, and Wellington is a big part of that story."

Biaggio formerly worked to prevent endangered tigers from killing villagers in Bangladesh.

"It's nice that our stakes are a lot lower. If we can find solutions in those scenarios, I'm sure we can find solutions here."