Professor Carolyn King's 50-year battle against stoats

Stoats and weasels were first introduced to New Zealand in the 1880s, here at Bushey Park, a 1039ha coastal Otago farm, northeast of Palmerston. Photo / Supplied

She loves weasels but was brought to New Zealand 50 years ago to help eradicate both weasels and stoats. Now, Emeritus Professor Carolyn King, while supporting the goal of a predator-free New Zealand by 2050, is warning against repeating mistakes that made Otago ground-zero for the disastrous introduction of those invasive predators 140 years ago. Otago Daily Times' Bruce Munro reports.

Bushey Park's main homestead is not visible from the unsealed start of the dusty drive that climbs and curves through a mature stand of trees.

Here at the old, pillared gateway, all that can be seen is a rabbit sunning itself that bolts from view as the car approaches.

Beyond the trees, on a north-facing lawn, is a large, gracious farmhouse built for Sir John McKenzie, one-time minister of lands.

Beyond it is the site of Bushey Park's first grand home, built for the farm's original colonial owner, Francis Rich.

Both spots look down across a large swathe of steep hills and rolling valley paddocks that comprise Bushey Park's attractive, 1039ha, coastal Otago property, bounded to the north by the Shag River and to the east by the Pacific Ocean.

The present owner, Jim Ironside, who runs beef and sheep on the land, said a resurgent plague of rabbits in Central Otago had not yet reached his farm.

Although the rabbit calicivirus, smuggled into New Zealand in 1997, is killing rabbits on his property later each year, it is still effective against the furry, pasture-ravaging pests.

Not so further inland where rabbit numbers have reportedly jumped five-fold during the past decade, causing serious problems for some farmers and vintners.

It was at Bushey Park almost 140 years ago that the first large-scale attempt to control rabbits in New Zealand began with the disastrous importation and release of stoats and weasels.

It was a much-needed but ill-conceived and unsuccessful cure that the country is still trying to coax back into its Pandora's box while New Zealand's wildlife continues to pay the price.

Carolyn King has never been to Bushey Park, despite spending plenty of time in the South Island, primarily in the beech forests of Fiordland and Tasman.

But the Waikato University emeritus professor of zoology knows better than anyone the history-shaping events that took place at this farm during the last quarter of the 19th century.

Prof King was headhunted to come to New Zealand, in 1971, after completing her doctorate on weasels at Oxford University.

She admitted to being "besotted" with weasels but said it was quickly made clear to her that her New Zealand job and career was to be focused on the eradication of weasels and stoats.

"I'm here because they were my favourite animal from the beginning, and I've been paid for 50 years to find better ways to kill them," King said.

For half a century, Emeritus Prof Carolyn King has been building knowledge to facilitate New Zealand's wildlife pest eradication efforts. Photo / Supplied

Stoats and weasels, both members of the mustelid family, which includes ferrets, have done enormous damage since being introduced.

Over millions of years, New Zealand had developed a "globally unique" feather and cold-blood-based ecosystem in which invertebrates, reptiles and birds filled all the ground-dwelling niches mammals occupied elsewhere, King said.

Stoats, which are more common here than weasels or ferrets, have been called "public enemy No 1" for New Zealand birds.

Stoats can take prey much larger than themselves and they hunt a diverse range of animals, including birds, mice, rats, lizards and invertebrates.

They kill an estimated 15,000 North Island brown kiwi chicks each year and are implicated in the extinction of several bird species including the South Island bush wren, laughing owl and New Zealand thrush.

In Otago, hoiho, mōhua and skinks have all declined, in part because of mustelids, especially stoats.

During her five-decade career, King has helped introduce more humane ways of trapping mustelids; researched and explained the complex interplay between beech forest growth cycles, native birds and their exotic predators; pointed to the formerly underestimated role of ship rats in decimating native bird populations, and highlighted the need to tackle mustelid fertility in order to eradicate them.

Along the way, she has unearthed the unfortunate series of events that put Otago's Bushey Park farm at the centre of New Zealand's own tragic, nationally significant version of "There was an old lady who swallowed a fly".

Rabbits were introduced to New Zealand for meat and sport from as early as the 1850s.

By the 1870s, they had reached plague proportions, threatening the viability of Southland and Otago farms, King wrote in a paper recently published in the New Zealand Journal of Zoology.

Then, in 1879, prominent Lincolnshire gentleman farmer Samuel Grant was given a taxpayer-funded trip to New Zealand by the colony's London-based agent-general Julius Vogel, to scope out a plan to bring out-of-work Lincolnshire farmers to New Zealand for a fresh start.

Grant owned various parcels of land, including near the town of Brigg, an important centre in the United Kingdom for rabbit breeding and the fur industry.

While touring New Zealand, Grant met Francis Rich who, during the previous, almost two decades, had developed Bushey Park as a leading sheep stud farm.

Rich was keen on introducing exotic animals for hunting, except rabbits, which he warned would become "a great evil", King said.

In 1881, Rich met up with Grant again in the UK and asked for help to bring stoats and weasels to New Zealand in the hope they would wipe out rabbits.

Grant contacted a skilled trapper he knew from Brigg, Walter Allbones, who then worked out how to trap and transport the mustelids without harming them.

In March 1883, Allbones arrived at Rich's estate, via Dunedin, with the first consignment of weasels and stoats, which were released at Bushey Park.

Not everyone thought this was a good idea.

King said conservationists led by Alfred Newton, George Grey and Walter Buller, as well scores of other thoughtful settlers and their friends in England, were all desperate to prevent the imminent catastrophe.

But the prospect of a stoat and weasel "quick fix" to the threat rabbits posed to the colony's pastoral economy won the day.

These late-19th-century Bushey Park workers likely include some who helped fight the plague of rabbits on the farm, which then-owner Francis Rich tried to tackle by introducing stoats and weasels to New Zealand. Photo / Waitaki Archive

The chief proponent of the mustelid plan was Benjamin Bayly.

He had lived in Otago in the 1860s, but from 1881 was based in Wellington where he was the government's superintending rabbit inspector.

In December 1883, Allbones was officially contracted by the government to import stoats and weasels for release in New Zealand.

The scheme, which was a failure because rabbits breed faster than mustelids, was eventually halted and Bayly demoted, but not until 1889.

The damage, however, had been done.

In the decade to 1892, at least 7838 living, wild stoats and weasels were brought to New Zealand under moves started by Grant, Rich and Bayly.

The "spider" was no cure for the "fly'. In fact, it was worse.

Stoats and weasels proved much more effective killers of New Zealand's native birds than they were of rabbits.

King said mustelids were the "natural enemies" of rabbits - "the product of an evolved interaction which includes ... mutually adaptive population dynamics" - whereas New Zealand's birds, which typically breed slowly, had no innate nest defences against the "new invaders", which included rats as well as mustelids.

"Suddenly ... reproduction is overwhelmed by unmanageable losses, as is illustrated by the long list of New Zealand's extinct birds," she said.

Ironside said he still sees the occasional stoat at Bushey Park, a distant relative of those first disastrous imports, "darting across a track on the farm".

So easily, it might all not have happened, Prof King said: If Lincolnshire farmers had not sent Grant to New Zealand; if Grant had not visited Rich during his nationwide tour; if Allbones had not been skilled enough to successfully transport mustelids; if Bayly had not been so convinced weasels and stoats were a good idea; if the New Zealand government had listened to the warnings of Buller and others ...

"The introduction of stoats and weasels into New Zealand was probably the single event most significant for conservation in the late 19th century," Prof King said.

"Perhaps within only another 25 years, conservation might have won the race. The outcome did indeed hang by a thread."

That alternate universe of the "ifs" did not happen.

Instead, New Zealand has native bush comparatively devoid of birdlife. And in the vacuum, a growing yearning to recapture what has been lost; a desire encapsulated in the government's 2016 commitment to a Predator-free New Zealand by 2050 (PF2050).

PF2050 has the ambitious goal of eradicating the most significant predator species — rats, mustelids and possums — from mainland New Zealand by 2050, despite the technology to achieve it still being in development.

Lincolnshire trapper Walter Allbones developed trapping and transportation methods to successfully export stoats and weasels to New Zealand in the 1880s. Photo / Allbones family album

King strongly supports PF2050.

"For New Zealanders, a deep longing to restore Aotearoa's lost dawn chorus has for decades been the widely agreed end," she wrote in her 2019 book Disaster on Four Small Paws.

But, she warns, we need to make sure we learn from past mistakes.

"Now, clear vision, knowledge of the past and steely determination are the first indispensable steps on the way to developing the unknown means."

Two key players in the formidable task are the Department of Conservation and Predator Free 2050 Ltd, a company set up by the government to fund research to develop the tools needed to do the job.

DoC technical adviser Bruce McKinlay said the department runs a substantial predator control programme, primarily using aerially-applied 1080 toxin and large-scale trapping to reduce predator numbers, including stoats and weasels.

Overall, DoC carries out predator control on about 1.5 million hectares of public conservation land.

In Otago, DoC and Forest and Bird trapping work includes hoiho nesting areas at Taiaroa Head on Otago Peninsula, Muttonbird (tītī) breeding areas on Otago Peninsula, and hoiho, little blue penguin and tītī breeding areas in the Catlins.

But trapping and poisoning predators is unlikely to succeed on its own.

Controlling fertility is thought to be the ultimate predator eradication strategy. And gene-drive technology is the hoped-for, fertility control, silver bullet.

It has long been theorised it would be possible to promote the inheritance of a particular gene to increase its frequency in a population.

If that gene ensured most of the offspring were male or most of the females were infertile, it would be a powerful, cheap, toxin-free way to remove a pest species.

In recent years, a gene drive technology, Crispr, has been developed that makes that a real possibility.

There has been some success with fruit flies and mosquitoes. And in recent months there have been some breakthroughs with mice, Predator Free 2050 science director Dr Dan Tompkins, of Dunedin, said.

But a gene drive solution for stoat and weasel eradication is still some way off.

"Some approaches, if successfully developed, may be available for some rodents in five to 10 years at the earliest," Tompkins said.

"Others (and other species, including mustelids) would take longer."

For King, the prospect of genetically modified pests being released into the wild at any point in the future raises significant concerns.

"There are people who know far more about genetics than I do ... and I have enormous confidence in them," she said.

"But my dilemma is New Zealand has a history of introducing self-perpetuating killing machines which, if they work are fine, but if they don't you're stuck with them because you can't recall them."

Key concerns, expressed by King and others, are that the modified genes might mutate in unexpected ways; that cross-breeding could allow the modified gene to be inherited by other animals; or, that the modified species could spread wider than intended, either accidentally or deliberately.

Gene-driven infertile female weasels would be a triumph in New Zealand but a catastrophe in the United Kingdom.

Gene drive techniques that have a more time-limited effect might overcome some of these potential pitfalls.

Tompkins said Predator Free 2050 was "keeping a close eye on these issues and contributing to international consideration of them" through involvement in the International Union for Conservation of Nature and the United Nations convention on biological diversity.

King implores everyone involved in trying to rid the country of pest predators not to lose sight of the lessons from their introduction 140 years ago at Bushey Park.

"We in New Zealand, above all people in the world, need to learn from our history and think about releasing self-perpetuating agents to do something in nature that we assume they will do.

"Bayly and the people who were making decisions at the time were responsible people; they were trying to do the best by New Zealand. But their worldview had a hard assumption that ... was incorrect.

"A gene drive, if we are very unlucky, could be the 21st-century equivalent of Bayly's plan to bring in stoats and weasels."