A Future Pest-free Paradise
by Wren Green

In this essay about the future of New Zealand conservation, biodiversity and policy consultant Wren Green takes a bold, hard look at how we manage introduced pests.

Attitude is important. When I envisage a possible future for pest management in New Zealand, a quote attributed to the German Goethe sets the right tone: “Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it.” The key words here are “dream” and “bold”, since we began pest management long ago.

Right from its beginnings, ingenuity – a travelling companion of boldness – has featured as well. Back in 1894, Richard Henry travelled to Resolution Island, the world’s first island sanctuary, as its newly appointed curator and caretaker. During his long sojourn there, Henry became a global pioneer of translocation techniques for rare endangered birds, particularly kiwi and kakapo. He ultimately left Resolution, despondent at the arrival of stoats that would undo his best efforts to provide a safe offshore island for endangered species, but his innovative techniques still inspire.

The Richard Henry self-resetting kill trap for rats,
oppossums and stoats has been developed by DOC.

Crown Copyright Department of Conservation

Te Papa Atawai Photo: Herb Christophers


Fast forward 70 years to 1964 and another defining bold moment in pest management. At the time, the conventional approach to protecting species was not particularly interventionist. Some writings by influential scientists and managers seemed more resigned to losing rare bird species than taking dramatic action to save them. And the ability of mammalian predators, especially rats and stoats, to eliminate populations or even species was not fully appreciated.

In 1964, a plague of rats threatened three rare bird species and a native bat that lived on Big South Cape, an island off Stewart Island (Rakiura). A few Wildlife Service field officers insisted that only urgent action to relocate these endangered species could save them. Others argued that this was unnecessary; the rat numbers would eventually go down. Nonetheless, a bold rescue operation went ahead and 36 rare South Island saddlebacks were successfully transferred to local rat-free islands. Translocations of the other two rare species, Stead’s bush wren and the local snipe, did not succeed and rats quickly killed off all the saddlebacks, bush wren, snipe and the unique native greater short-tailed bat left on Big South Cape. These three extinctions, and the dramatic rescue of the saddleback, was a wake-up call for conservation managers everywhere.

Hard lessons were learned: introduced predators can drive native species to extinction; off-shore islands can be essential refuges for vulnerable species; translocations can work; scientific authorities don’t always know best. Ridding offshore islands of pests to provide havens for other species then became one of the successful tools for conservation management.

One thing conservationists should do more often, in my opinion, is take the time to reflect on what their campaigns and actions have achieved – while acknowledging the part played by researchers and innovative management practices. When we do so, we can list some remarkable achievements since the 60s. For example: rat eradiation from Breaksea Island (170ha) in 1988 – then a world-first for large islands; the ingenuity of Don Merton and colleagues in rescuing the black robin from extinction; eradicating possums and rats from Kapiti Island (1965ha); dozens of eradications of mice, stoats, rats, deer, feral cats and possums from islands, followed by numerous successful transfers of birds, lizards and insects.

Arid Island (Rakitu) some 5kms off the NE Barrier Coastline
is being considered for eradication of rats.  Photo: IslandStay

In 2001, little more than a decade after clearing rats off Breaksea Island, DOC took on the bold dream of eradicating rats from Campbell Island, a massive 11,300ha sub-Antarctic island. Two years in the planning, and faced with novel logistical and technical challenges, the eradication was declared a success in 2005. Other countries now contemplate clearing large islands of pests that had previously been thought impossible. Sir David Bellamy has said: “New Zealand is the only country which has turned pest eradication into an export industry.” This reputation owes much to the innovative research and can-do attitude that has turned visions into reality.

Then people boldly asked “If we can do it on offshore islands, can we do it on the mainland?” This led to research during the 1990s into the feasibility of managing pests at low enough numbers in isolated areas of forest to benefit threatened species. The mainland islands model was born. Unfenced mainland islands were followed by private and innovative initiatives creating islands of habitat surrounded by predator-proof fences from which pests were removed. Conservationists can take pride in their successful efforts to eliminate possums and other predators from Bushy Park and protect the increased kereru and kaka populations with a predator-proof fence around the whole area. However, high capital and maintenance costs limit the options for predator-proof fences. They are not a viable option for the larger landscapes over which ecosystems need to be managed and should not be held up as alternatives to the large-scale issues.

What might further research and technological advances in pest control allow us to boldly dream for tomorrow’s conservation goals? Pest management options fall into three basic classes – physical, chemical and biological. There is a new generation of physical “smart traps” (Forest & Bird magazine, November 2010) that shows how far trap technology has advanced from the days of the cruel Lanes Ace leg trap. Cheaper, humane, resetting kill-traps for rats, stoats and possums are being tested now. With further investment and development, they could revolutionise pest management by drastically cutting the labour costs that trapping currently requires.

The chemical control option means using poisons. The current stand-out issue here is the aerial distribution of 1080 to control several different mammalian pests. In the Past 30 years there have been many technological improvements in bait manufacture, guidance systems for pilots and improved sowing buckets to spread baits. Field research has improved our understanding of how to increase the acceptability of poisons, including 1080, to possums, rabbits, rats and stoats.

The outcome of all these incremental improvements is best demonstrated by comparing how much 1080 bait was used in aerial operations in the 1970s compared with today. Success rates have improved to over 95 percent reductions in possum, rat and stoat numbers while the amount of bait used has dropped from 25kg of bait per hectare to 2-3kg per hectare. Spreading 2kg of pellet baits over a hectare is equivalent to dropping four baits on a doubles tennis court. With few baits per unit area, the risks of by-kill of non-target species is now much lower than before.
Despite the high development and registration costs, work continues on new toxins. One acts on red blood cells to cut their ability to carry oxygen around the body. Early research results suggest it may be an effective and humane toxin for stoat control. The most acceptable toxin is one that is cheap, humane and species specific – and effective. We do not have it yet, but it is a goal worth pursuing.

I am less optimistic about biological controls being developed for the nasty pest trio of possums, rats and stoats – at least in the foreseeable future. After many millions of dollars, research on a biological control for possums has been stopped. Biological control did help to significantly reduce rabbit numbers after the illegal introduction of rabbit calicivirus. However, the effectiveness of the virus has weakened over time and those farmers who did little to complement it with conventional rabbit control now face high rabbit numbers again. The lesson is not to expect research to deliver a quick-fix silver bullet for our mammalian pest problems.

With further major improvements in traps and toxins, what bold visions might we dream and what barriers could get in our way? First, let’s think about even bigger islands from which pests might be eradicated. At 28,500ha, Great Barrier Island has rats, mice and feral cats, but no possums or mustelids. In a decade or two we may have a super, self-setting rodent trap that could do the job. Perhaps a combination of next-generation anti-coagulants and rolling lines of traps along the island could achieve what now seems impossible.

The whitehead (Mohoua albacilla) - high on the
list of species to re-introduce to GBI.
Crown Copyright Department of Conservation

Te Papa Atawai Photo: Joseph Fraser


After clearing the North Island’s largest offshore island of predators, a bigger challenge would be clearing Stewart Island of predators. Imagine the translocation options that would open up. Rakiura National Park would be home to the many surplus kakapo from Codfish Island, along with lots of kokako, kaka and other threatened species from other managed areas. Before long, the restored dawn chorus and local increase in kiwi numbers would draw visitors to Stewart Island from New Zealand and beyond.

Study a map of New Zealand, and its geography suggests other audacious visions. How about using the urban sprawl and squeezed neck of Auckland as a barrier and clear the farmlands and forests from there to Cape Reinga of possums and stoats? Northland is home to important kiwi populations and most of these are on private, not conservation lands. Given the threats to wild kiwi populations throughout New Zealand, this could provide safe areas at a new order of magnitude for our national bird to thrive. Might Coromandel Peninsula and the bulge of Taranaki, both important areas for biodiversity, also be capable of effective “isolation” followed by intensive knockdown or eradication of major pests?

Thinking about pest management only in an island context is too limiting for the larger systemic issues we face in New Zealand. First, most of our threatened biodiversity is in places where the island treatment is not feasible or is prohibitively expensive at present. Second, islands are “out there”, whereas we live “in here”, where competing political and social influences and attitudes are more complex. It is how we change our thinking about pest management “in here” that will support or stunt bold dreams for the future. I suggest this is the fundamentally important transformation we need, supported by ongoing technical advances that will be needed to realise such dreams.

Several relevant factors underpin this transformation and they may change in ways that make it possible. These factors are:
• Shifts in ecological thinking
• Changes in values and engagement
• New governance arrangements
• Maori-Pakeha dialogues

Ecological science has undergone an important shift in emphasis and perspective in the past two decades. The earlier belief that ecosystems naturally tend towards conditions of equilibrium has shifted to understanding ecosystems as dynamic systems, capable of rapid and unexpected changes. This is particularly true in New Zealand with our geological instabilities, exposure to cyclones, droughts and floods, now overlaid with the diverse impacts of introduced plants and animals.

Management and biodiversity policies based on equilibrium assumptions can be inappropriate for dynamic and unpredictable systems. Understanding dynamic systems requires a greater knowledge of ecological processes and how key species respond to change. For example, discovering that kereru play a major role in the dispersal of forest seeds and therefore in the regeneration of forest ecosystems means their management is as relevant to maintaining the overall health of forests as it is about conserving a species. Since our primary production industries and tourism ultimately rely on the health of our biodiversity, greater research effort into understanding these ecosystem dynamics to improve their management would be a smart investment.

As David Young describes in Our Islands, Our Selves, attitudes to conservation change over time, reflecting and shaping broader social values. Walter Buller’s Eurocentric and pessimistic views on ‘inferior’ native species and their likely demise have long since been marginalised. New Zealanders increasingly value indigenous plants and animals. The rapid growth in the number of community groups dedicated to looking after local reserves, protecting breeding sites, starting restoration projects, restoring wetlands or opposing environmentally destructive practices attests to this.

Changing social values towards native biodiversity are occurring at a time when traditional arrangements of hierarchical government are being questioned and contested. The dominant model of top-down, expert-driven, government-led policies and practices is increasingly challenged across areas as diverse as agriculture, transport, energy, health, climate change and conservation management. These global trends reflect the increasing complexity of socio-environmental problems and the unprecedented ability of civil society to access and share knowledge and information, something governments used to control and regulate to a far greater extent than now.

Kokako (Here being radio transmitter banded) have been successfully introduced into a rat-managed area in the Waitakere Ranges.
Crown Copyright Department of Conservation

Te Papa Atawai Photo: Herb Christophers


As a consequence, new approaches to governance are being tried that are more flexible, adaptive and responsive to stakeholder values and interests than is possible under older hierarchical structures. These developments are particularly relevant for adaptive management approaches which, in turn, are appropriate for studying dynamic systems. The success of adaptive management requires new ways for management agencies, stakeholders, interest groups and researchers to work together, including on pest control, such as deer or possum issues. By doing so, different voices can be heard and reflected in management goals. As the late Geoff Park has written: “Good management will require public dialogue as much as expert opinion because the definition of goals and development of scientific understanding is an interactive and experimental process.”

Management staff, scientists and communities have already shown that these new approaches can succeed. Even the contentious issue of aerial use of 1080 has been worked through in some places with the input of all parties to arrive at acceptable solutions. If the will is there on all sides, solutions can be found. New Zealanders, whether for or against 1080, value their native forests and birdlife and support pest control. They only disagree on the methods. With agreement on the goal, surely the rest is just detail?

I have left the impact of Maori-Pakeha dialogues to last, not because it is least important but because the other influences I have discussed all provide the context within which Maori-Pakeha dialogues on conservation, including pest management, are best considered. In the opening article in this series (Forest & Bird, November 2010), David Young proposed that Forest & Bird would need “to step up to a new level of relationship with iwi and hapu”, noting that the Waitangi Tribunal’s Wai 262 report on the claim on indigenous flora and fauna would provide an opportunity to do so. This report is due out this month and a constructive response will require more New Zealanders than just Forest & Bird to step up.

I look forward to a dialogue on how Maori spiritual and cultural values, as well as their holistic concepts, such the principles of mauri, connectedness, ecological harmony, continuity and reciprocity can inform the way we approach ecological studies and pest management. A leading scholar, Mason Durie, has argued that these principles can be measured quantitatively even though they are often seen as spiritual. Durie also writes: “Essentially value is a function of relationships …” Pakeha relationships with Aotearoa and its wildlife will deepen as the centuries pass and therefore Pakeha values will change along the way. We are ready for a dialogue that builds a better understanding of the connections between Maori and Pakeha values because that will provide a stronger basis for new governance arrangements and partnerships with Maori for conservation and pest management. The Wai 262 report may provide the stimulus for this to happen, but we should be planning it anyway.

Some may view these developments with alarm. I see them as positive opportunities. In 2050, we should be able to look back with pride on achievements since 2011: dramatic improvements in control technologies that enabled eradication of pests on a scale previously thought impossible; generous budgets to support biodiversity research and management on public and private land by governments that finally appreciated the economic sense of this as smart investments; many new partnerships and co-management arrangements between Maori, communities and agencies that are successfully managing for biodiversity and minimal pest impacts; a deafening dawn chorus when families greet the morning sun and renew their spirits in their local forest, wherever that may be.


Wren Green researched possums for the Forest Research Institute before joining the Department of Conservation in 1987. He has been consulting since 1997 in areas including biodiversity, biosecurity, sustainable development, science policy and climate change.