Nat­u­ral born killers

More ef­fec­tive poi­sons and long-life su­per­lures are among the meth­ods be­ing looked at in a bid to rid the coun­try of the pests that kill thou­sands of na­tive birds each year.

New Zealand Listener - - CONTENTS - By Re­becca Mac­fie

Long-life su­per-lures and bet­ter poi­sons are among the meth­ods be­ing looked at to rid the coun­try of the pests that kill thou­sands of na­tive birds each year.

The tiny killers are still in their dens, suck­ling on moth­ers’ milk and primed for a sea­son of slaugh­ter. In an abun­dant “mast” year such as the cur­rent sea­son, each adult fe­male stoat will have given birth in Oc­to­ber to eight or 10 – per­haps as many as 15 – healthy kits. Within the ba­bies’ first weeks, while they’re still blind, deaf and im­mo­bile, an adult male will have vis­ited the den and im­preg­nated all the fe­male young.

By Christ­mas, they will be weaned and ma­raud­ing close to the den, pre­par­ing for life as in­de­pen­dent car­ni­vores at the top of the per­verted for­est food chain. By Jan­uary, they will be on their own, fan­ning out across large dis­tances; in the Eglin­ton Val­ley in Fiord­land, a tagged young fe­male stoat was once found to have trav­elled 65km in less than a month.

Their en­try into the ecosys­tem will mark a greater than five­fold in­crease in the stoat pop­u­la­tion. No source of pro­tein will be safe from these ath­letic, in­tel­li­gent and vo­ra­cious hunters.

“First, they eat the kiwi chicks,” says De­part­ment of Con­ser­va­tion sci­en­tist Josh Kemp. “Take a Haast tokoeka – just beau­ti­ful prey for a stoat. They leave a big trail of scent along the ground. The stoat doesn’t have to climb a tree to get it. The kiwi’s nat­u­ral re­sponse [to threat] is to freeze, and that’s 300-400g of meat for a 200-300g stoat – enough to last a few days.”

Up to 60% of kiwi chicks are eaten by stoats, but they take prey of all sizes: hole-dwelling birds such as mo­hua and kakariki, ground-feed­ing robins, bats, lizards, frogs and weta, as well as the mice and rats that are at plague pro­por­tions in this year of plenty. “The young stoats will just try ev­ery­thing,” says Kemp.

Larger birds such as kea, kaka and whio will be largely off the menu – un­til later. They will be­come prey when the on­set of win­ter causes the rat and mice pop­u­la­tion to crash, de­priv­ing the stoats of a large source of nu­tri­tion.

“That’s when we see adult kea and even takahe be­ing taken on,” says Kemp. “Kea and whio nest in Au­gust, and the stoat plague cuts their pro­duc­tiv­ity to zero. We have footage from cam­eras in­side a kea nest where she lays an egg, and the stoat nicks it; she lays an­other, and the stoat nicks it again … Blue ducks [whio] are the same. And for both those species, we also see an in­crease in adult mor­tal­ity. Dur­ing stoat plague events, takahe weigh­ing 1.5 or 2kg have been taken.”


The stoat plague that is about to ir­rupt through our forests dur­ing the sum­mer of 2017 will mark the

While the ba­bies are still blind, deaf and im­mo­bile, an adult male will have vis­ited the den and im­preg­nated all the fe­male young.

fi­nal phase of a re­peat­ing cy­cle of dev­as­ta­tion that takes two years from be­gin­ning to end. It kicks off with a heavy spring flow­er­ing of beech trees (called a mast, de­rived from the Old English word “maest”, mean­ing the nuts and seeds on the for­est floor), pro­duc­ing an abun­dance of high-pro­tein seeds and pollen, which sup­ports fe­cun­dity among en­demic birds and in­ver­te­brates, as well as in­tro­duced preda­tors.

Mast years have been thought to oc­cur ev­ery four to six years, although the 2016 mast has come just two years after the pre­vi­ous one, and there are signs that 2017 may be an­other. The years 1999 and 2000 brought two masts in suc­ces­sion.

From the Jan­uary fol­low­ing a heavy spring flow­er­ing, ro­dent num­bers ex­plode. With rats and mice pro­duc­ing lit­ters of six to eight, and young fe­males breed­ing from about three months and yield­ing up to four lit­ters a year, the pop­u­la­tion grows by 1.2% ev­ery day dur­ing a mast, says Kemp.

The for­est floor re­mains a rich larder of nour­ish­ing seeds through­out a mast win­ter such as 2016’s, al­low­ing con­tin­ued ex­po­nen­tial growth in num­bers of rats and mice. But in late spring, the seeds ger­mi­nate and the pro­tein source van­ishes.

“The rug is sud­denly pulled out from un­der them,” says Kemp. “They’ve been liv­ing in the lolly jar all year, breed­ing up, liv­ing at very close quar­ters. Then sud­denly – bam! – within a few weeks it’s all over.”

As plenty turns to want, “ev­ery­thing is at risk”, he says. The rodents’ highly struc­tured so­cial sys­tem comes un­der acute stress, with ev­i­dence of rats fight­ing each other for re­sources. “At that point, the rats stop breed­ing, but they don’t all die. So you have a pop­u­la­tion of big hun­gry rats … and this co­in­cides with when a lot of birds are lay­ing eggs. Robins, fan­tails, tomtits all start breed­ing around Au­gust and Septem­ber. The mo­hua start nest­ing in late Oc­to­ber and Novem­ber, so they get an ab­so­lute past­ing. Kakariki are nest­ing in their knot holes right through this, so they are heav­ily preyed upon.”

Also on the list of en­demic species that are sud­denly acutely vul­ner­a­ble to rav­en­ous rats are the brown creeper, grey war­bler, kokako and long- and short-tailed bats.


With­out hu­man in­ter­ven­tion to knock back ro­dent num­bers, they cut like a scythe through na­tive pop­u­la­tions. “With no con­trol, in a high-mag­ni­tude rat ir­rup­tion, you can ex­pect zero pro­duc­tiv­ity. All the nests will be preyed upon, and you can ex­pect some loss of adult birds,” says Kemp.

“A 20-50% loss of to­tal pop­u­la­tion, or more, can be ex­pected. In 2006, we left a por­tion of the Dart-Route­burn mo­hua un­treated for sci­en­tific rea­sons. It ba­si­cally went ex­tinct in one sea­son, as did the Eglin­ton mo­hua pop­u­la­tion when we left it to face the rat plague of 2001. In 2009, we had a par­tial mast in the Dart-Route­burn and left the whole mo­hua un­man­aged, think­ing the rat ir­rup­tion would be rel­a­tively mi­nor. We lost about half the mo­hua. We don’t need to re­peat those lessons any more.”

And while the rats are sat­is­fy­ing their ap­petites with lit­tle birds and eggs, the fe­male stoats – well-nourished on their plen­ti­ful mast win­ter diet of rats and mice – are giv­ing birth to bumper lit­ters, which will soon emerge to take their place in the cy­cle of de­struc­tion.

Jan Wright, the Par­lia­men­tary Com­mis­sioner for the En­vi­ron­ment, de­scribed the mod­ern-day mast phe­nom­e­non in a 2011 re­port as “death in a time of plenty”.

She de­scribed it as a “tragic irony” that the con­di­tions to which our na­tive species have evolved over tens of mil­lions of years to boost their birth rates are the very con­di­tions in which in­tro­duced preda­tors com­mit their worst slaugh­ter. The breed­ing pat­terns of many na­tive birds have evolved around the mast cy­cle – the kaka and the kakapo will breed only in a mast year, and other species such as kakariki will triple their usual breed­ing ef­fort in mast years be­cause of the greater avail­abil­ity of food.

But evo­lu­tion has been hi­jacked by the in­vaders: what ought to be a sea­son of preser­va­tion and ex­pan­sion for our wildlife has been trans­formed into a fast track to ex­tinc­tion.

Track­ing down and killing just three stoats that had made their way onto pest-free Kapiti Is­land in 2010 cost $600,000.


The good news is that the mast phe­nom­e­non – par­tic­u­larly in South Is­land beech forests – is in­creas­ingly well un­der­stood. In 2012, sci­en­tists de­vel­oped a model that helps pre­dict mast years, which ap­pear to be trig­gered by a sum­mer that is a de­gree or so warmer than the pre­vi­ous sum­mer, says DoC sci­en­tist Graeme El­liott.

But there is plenty of bad news, in­clud­ing the fact that cli­mate change is bring­ing grad­u­ally in­creas­ing tem­per­a­tures. There­fore the chances of one sum­mer be­ing hot­ter than the pre­vi­ous – trig­ger­ing a mast – are also in­creas­ing.

And although ecol­o­gists’ un­der­stand­ing of mast-year dev­as­ta­tion has in­creased, en­abling more strate­gic aerial 1080 drops to cut down ro­dent and stoat plagues (the car­niv­o­rous stoats die when they eat the poi­soned rodents), only a small frac­tion of the coun­try is un­der any kind of sys­tem­atic preda­tor con­trol.

Bat­tle for Our Birds, the cam­paign launched by DoC to push back the plagues of in­vaders in the 2014 mast year, sig­nalled a more fo­cused ap­proach to preda­tor con­trol by the de­part­ment. It has been fur­ther ex­panded this year to cover 840,000ha, up from 694,000ha in 2014.

But that’s less than 10% of the to­tal DoC es­tate, and Kemp says only a quar­ter of South Is­land forests with mast­ing beech trees will re­ceive any kind of preda­tor con­trol this year.

The de­part­ment’s in­ad­e­quacy at hold­ing back the tide of ex­tinc­tion has been well­doc­u­mented, with the an­nual death toll from stoats, rats and pos­sums put at 26.6 mil­lion chicks and birds.

Wright, who re­searched the use of 1080 in 2011 and con­cluded that the de­part­ment needed to use much more of it, was shocked to dis­cover how lit­tle pest con­trol was go­ing on. In a fol­low-up re­port, she noted that the de­part­ment al­lo­cated more fund­ing to re­search­ing 1080 and its al­ter­na­tives than it did to pest con­trol us­ing the toxin.

With­out DoC’s con­certed ac­tion, she fore­saw a grim fu­ture in which sur­viv­ing frag­ments of our unique bio­di­ver­sity, which evolved in iso­la­tion over 80 mil­lion years with­out the pres­ence of preda­tory mam­mals, would ex­ist only on off­shore is­lands and be­hind costly main­land sanc­tu­ary fences. Our na­tional icon, the kiwi, was de­clin­ing in ar­eas with no pest con­trol at be­tween 2% and 6% a year, she re­ported – fast enough to be gone within a gen­er­a­tion.

New Zealand con­ser­va­tion­ists and sci­en­tists have won global renown for bring­ing species back from the edge of ex­tinc­tion – among them the black robin, takahe and kakapo – yet this coun­try has the du­bi­ous dis­tinc­tion of hav­ing one of the high­est pro­por­tions of threat­ened species in the world.

And while na­tive ecosys­tems con­tinue to be dev­as­tated by preda­tors, DoC – the coun­try’s bio­di­ver­sity guardian – has it­self lived through waves of re­struc­tur­ing, shrink­ing re­search spend­ing and the

“The kiwi’s nat­u­ral re­sponse [to threat] is to freeze, and that’s 300-400g of meat for a 200-300g stoat.”

loss of core sci­en­tific ex­per­tise, in­clud­ing threat­ened-species and pest-erad­i­ca­tion spe­cial­ists. Un­der suc­ces­sive DoC man­age­ment regimes, “sci­ence was sim­ply seen as get­ting in the way of the pol­i­tics”, says for­mer DoC bio­di­ver­sity ex­pert Theo Stephens, who quit dur­ing the sweep­ing 2012 re­struc­tur­ing over­seen by for­mer di­rec­tor-gen­eral Al Morrison.

Few peo­ple ex­em­plify the flim­si­ness of DoC’s thin green line of de­fence against in­va­sive preda­tors as vividly as park ranger Evan Smith. Work­ing at Lake Macken­zie Hut on the spec­tac­u­lar Route­burn Track, he de­spaired at the dam­age stoats were do­ing to the birdlife in his area, which re­ceived no DoC preda­tor con­trol. So he started putting out his own traps, and in his evening hut talks he would ex­plain the prob­lem to tram­pers and ask for dona­tions to buy more traps.

Four years since the start of Smith’s des­per­ate cam­paign, 2000 tram­pers have opened their wal­lets to help out, his trap line ex­tends 20km, and the de­part­ment’s spin doc­tors have cast him as a back­coun­try folk hero. DoC di­rec­tor-gen­eral Lou San­son cred­its him as a great sto­ry­teller, but ad­mits he was “em­bar­rassed” to find when he took on the de­part­ment’s top job in 2013 that “we are beg­ging for peo­ple to help bring back our birds”.


Now, after years of be­ing pushed closer to ex­tinc­tion by in­vad­ing preda­tors – de­fended by an earnest home guard of vol­un­teer con­ser­va­tion groups, over­stretched DoC front-lin­ers and agri­cul­tural con­trac­tors tar­get­ing TB-car­ry­ing pos­sums – our en­dan­gered species sud­denly have al­lies in high places.

In July, Prime Min­is­ter John Key and four Cab­i­net min­is­ters – in­clud­ing Eco­nomic De­vel­op­ment and As­so­ciate Fi­nance Min­is­ter Steven Joyce and Con­ser­va­tion Min­is­ter Mag­gie Barry – trooped up to Zealan­dia wildlife sanc­tu­ary in Wellington to de­clare that by 2050 the coun­try would be “com­pletely free” of rats, stoats and pos­sums.

The an­nounce­ment came out of the blue and re­ceived mas­sive in­ter­na­tional pickup, with cov­er­age in out­lets rang­ing from the Econ­o­mist and Al Jazeera to Vice News and Time.

But with an up­front Gov­ern­ment in­vest­ment of just $7 mil­lion a year over the next four years, is it to be taken se­ri­ously? In a re­cent New Zealand Jour­nal of Ecol­ogy pa­per, for­mer Land­care ecol­o­gist John Parkes, who has worked on pest-erad­i­ca­tion projects here and around the world, cal­cu­lated the price tag of rid­ding the coun­try of ev­ery last rat, stoat and pos­sum at $32 bil­lion, based on the per-hectare cost of clear­ing pests off Rangi­toto and Mo­tu­tapu is­lands in Auck­land’s Hau­raki Gulf.

Oth­ers have come up with lower – but still enor­mous – num­bers: a pa­per by sci­en­tist James Rus­sell in BioS­cience put the likely cost at be­tween $5.5 bil­lion and $26.2 bil­lion in 2013 dol­lars. Track­ing down and killing just three stoats that had made their way on to pest-free Kapiti Is­land in 2010 cost $600,000.

So, was the big Zealan­dia an­nounce­ment just a cyn­i­cal dis­trac­tion from a win­ter of dis­con­tent that saw the Auck­land hous­ing mar­ket spi­ral out of con­trol, with daily sto­ries of fam­i­lies liv­ing in cars?

And if there is a gen­uine in­ter­est in sav­ing our ex­tra­or­di­nary bio­di­ver­sity, from where did this un­ex­pected rush of in­ter­est and en­thu­si­asm come?

San­son says the dec­la­ra­tion of the Preda­tor Free 2050 vi­sion is the prod­uct of “a thou­sand small sto­ries com­ing to­gether in a wave. The coun­try was head­ing down a wave, and the Gov­ern­ment has come on to the wave.”

In San­son’s telling, that “wave” be­gan in 1988 when a group of then-Wildlife Ser­vice rangers eradicated a 170ha Fiord­land is­land, Break­sea, of rats. “Then by 2002, we had done the largest is­land erad­i­ca­tion in the world, Campbell Is­land [the re­mote 11,300ha is­land had been in­fested with up to 200,000 rats] … So in the space of 14 years, we had be­come world lead­ers, and there is scarcely an is­land erad­i­ca­tion op­er­a­tion in the world that doesn’t have an ex-DoC ranger or a Kiwi he­li­copter pi­lot.”


The con­cept of fenced main­land is­lands – ex­em­pli­fied by Zealan­dia and the Sanc­tu­ary Moun­tain Maun­gatau­tari re­serve in Waikato – also started build­ing mo­men­tum, and com­mu­nity trap­ping groups sprang up in their hun­dreds through­out the coun­try. Friends of Flora, which formed after the dev­as­ta­tion of the 1999 beech mast in Kahu­rangi Na­tional Park, is one of the old­est such groups and now traps 8000ha of the 452,000ha park. The vol­un­teers’ ef­forts have re­stored the whio pop­u­la­tion in Flora Stream, the group are six years into a project to re­lo­cate great spot­ted kiwi into the area, and they have man­aged to hold the line against fur­ther loss of bird species.

More re­cently, busi­ness and phil­an­thropic in­ter­ests have been start­ing to come to the de­fence of threat­ened bio­di­ver­sity. One of the most per­sis­tent voices for ac­tion was Les Kelly, a New Zealand busi­ness­man who re­turned home after years of liv­ing in Aus­tralia and was dis­mayed to dis­cover the forests had fallen silent dur­ing his decades away. He be­gan ham­mer­ing on the doors of movers and shak­ers and, ac­cord­ing to one of his key al­lies, DoC sci­en­tist Paul “Scratch” Jansen, helped build a “groundswell of key in­flu­encers”. Among those he rarked up were For­est & Bird, which in turn hosted a 2012 gath­er­ing of ecol­o­gists and preda­tor ex­perts from DoC, re­gional coun­cils, Ospri [for­merly the An­i­mal Health Board], uni­ver­si­ties and Land­care Re­search.

By morn­ing tea time on the first day of the meet­ing, each of the preda­tor ex­perts had agreed it was tech­ni­cally (if not fi­nan­cially or so­cially) pos­si­ble to rid the coun­try of in­va­sive pests. “It was a won­der­ful mo­ment,” re­calls Kevin Hack­well, For­est & Bird ad­vo­cacy man­ager. “You saw light bulbs go­ing on around the room. Up un­til then,

ev­ery­one had been in the con­trol par­a­digm on the main­land – that pest con­trol will be for­ever, that we’ll get bet­ter at it, but that it will be this con­stant prob­lem that we will al­ways be deal­ing with.”


The no­tion that New Zealand could do bet­ter than wag­ing an end­less los­ing de­fence against the in­vaders was ar­tic­u­lated most pow­er­fully by sci­en­tist Sir Paul Cal­laghan shortly be­fore he died in 2012. In a speech at Zealan­dia, he spoke of the coun­try’s unique biota in the same breath as Bri­tain’s Stone­henge, the Great Wall of China and the pre­his­toric cave paint­ings of cen­tral France. But this rich her­itage was im­per­illed, he warned: “The sit­u­a­tion has never been as bad as it is now. We are fac­ing ut­ter catas­tro­phe in our forests.”

He con­ceived of a New Zealand-style “Apollo mis­sion” – a ref­er­ence to the US’s gal­vanis­ing vi­sion to put a man on the Moon. De­scrib­ing a preda­tor-free New Zealand as this coun­try’s “moon­shot”, he said: “We can do this.”

At about the same time, phi­lan­thropists started pour­ing se­ri­ous money into the war on pests. At Sep­a­ra­tion Point in Abel Tas­man Na­tional Park, a pop­u­la­tion of plas­tic gan­nets sud­denly ap­peared three years ago – a bid to lure real gan­nets, and one of the early tan­gi­ble signs of an am­bi­tious $25 mil­lion project to re­store the park’s ecol­ogy over the next 30 years. Funded by North­land in­dus­tri­al­ists Neal and An­nette Plow­man, Project Jan­szoon has rein­tro­duced kaka and kakariki, has knocked back wild­ing pines and by next year will have the en­tire park stoat-trapped along­side an Air New Zealand­backed trap­ping cam­paign in the north­ern area of the park.

Through their Next Foun­da­tion, the Plow­mans are also fund­ing (along­side oth­ers, in­clud­ing lo­cal iwi, Shell and tech­nol­ogy en­tre­pre­neur Sam Mor­gan) the Taranaki Mounga project to clear in­va­sive pests and weeds from 34,000ha around Mt Taranaki. Next is also a foun­da­tion fun­der (along with the Mor­gan Foun­da­tion and a clutch of dairy com­pa­nies) of Zero In­va­sive Preda­tors (Zip), which is fo­cused on de­vel­op­ing new tech­niques for mon­i­tor­ing and trap­ping rats, stoats and pos­sums, and has achieved the to­tal erad­i­ca­tion of pests from the 400ha Bot­tle Rock Penin­sula in the Marl­bor­ough Sounds with­out erect­ing a preda­tor fence.

In Hawke’s Bay, wealthy phi­lan­thropist Ju­lian Robert­son is back­ing the 26,000ha City to Cape eco­log­i­cal restora­tion project, and the Re­con­nect­ing North­land bio­di­ver­sity project has fund­ing from Sir Stephen Tin­dall. The Mor­gan Foun­da­tion is fund­ing projects such as Preda­tor Free Ste­wart Is­land/ Rak­iura and the Mil­lion Dol­lar Mouse project to rid the An­tipodes Is­land of mice.

Stand­ing up for na­tive species is no longer the pre­serve of “gree­nies” and be­lea­guered DoC rangers. The most in­flu­en­tial con­ser­va­tion­ists now wear suits and have di­rect links to the Bee­hive. Sir Rob Fen­wick, the founder of the Liv­ing Earth com­post­ing busi­ness, and chair­man of the Preda­tor Free New Zealand and Ki­wis for Kiwi trusts, re­calls tak­ing

John Key to a kiwi re­lease in late 2014 and telling the Prime Min­is­ter that the na­tional icon was de­clin­ing at 2% a year.

“I said, ‘Look, Prime Min­is­ter, these birds will be ex­tinct in your grand­chil­dren’s life­time’ … He was vis­i­bly shocked and said, ‘Well, what would plus 2% be like?’ You kick your­self for not ask­ing the ques­tion your­self,” re­calls Fen­wick. “But we went away and got Land­care [Re­search] to do a re­port that an­swered that ques­tion, and ac­tu­ally, it’s not that hard. There was a man­age­able way through this.”

The Preda­tor Free New Zealand trust was set up by Fen­wick with DoC back­ing in 2013 to help co-or­di­nate vol­un­tary, iwi and landowner con­ser­va­tion ef­forts around the coun­try. So far, it has mapped 800 com­mu­nity trap­ping and pest-con­trol groups. “We reckon 200,000 New Zealan­ders have done some kind of vol­un­tary work for con­ser­va­tion in the past 12 months,” says Fen­wick.

The fi­nal push that hoisted New Zealand’s en­dan­gered species on to the po­lit­i­cal agenda came with the de­vel­op­ment by DoC of a busi­ness case tai­lored to ap­peal to Cab­i­net deal­maker Steven Joyce. The doc­u­ment tot­ted up the on­go­ing cost of preda­tor con­trol ($94 mil­lion a year, 70% of which is spent killing TB-car­ry­ing pos­sums that threaten agri­cul­ture) and agri­cul­tural losses caused by pests ($52 mil­lion a year). It pushed the idea of an “in­vest­ment ap­proach” to con­ser­va­tion, with “busi­ness fund­ing and en­tre­pre­neur­ial pace” aug­ment­ing the coun­try’s long his­tory of preda­tor con­trol. By set­ting up a pub­lic-pri­vate part­ner­ship named Preda­tor Free New Zealand to act as “part pro­moter, part bro­ker and part in­vestor”, phil­an­thropic and cor­po­rate fund­ing and com­mu­nity ef­fort could be lever­aged to de­velop faster and more ef­fi­cient meth­ods of purg­ing the land of pests.

The plan en­vis­ages that for ev­ery $1 of Gov­ern­ment money, $2 of pri­vate-sec­tor money will be stumped up. US-based busi­ness­man Chris Lid­dell, who chairs the Next Foun­da­tion, sup­ports the pro­posed model and hopes it will draw more pri­vate phil­an­thropic money out of the wood­work. And he says the preda­tor-free goal has been “no­ticed” in the US, where he has had pre­lim­i­nary con­ver­sa­tions with two or three po­ten­tial fun­ders.

“I have started talk­ing to foun­da­tions and say­ing, ‘If you want to spend some money in a coun­try which has got a big na­tional goal, where … there is no cor­rup­tion and a high de­gree of in­tegrity, and cre­ate a very pos­i­tive en­vi­ron­men­tal im­pact, then you should look at New Zealand.”


“I think ev­ery New Zealan­der who wakes up and hears a tui in the back gar­den thinks, ‘Wow, I’m proud to be a Kiwi’ … This is about our iden­tity,” says San­son. “We are the only coun­try in the world that’s a land of birds, and in 1880 when we brought those stoats in, we just did so much dam­age. Peo­ple want that coun­try back. We will be ul­ti­mately the Gala­pa­gos of the world if we can do this.”

But it’s a mon­u­men­tal “if”.

As Rus­sell wrote in Bio­Sci­ence, “50 years of pioneer­ing and per­sis­tent ef­fort” in which New Zealand has eradicated all in­tro­duced mam­mals from 100 of its off­shore is­lands “has still only in­creased the pest-free is­land area from 0.5% to just 10%”. Eco-sanc­tu­ar­ies ac­count for just 0.2% of New Zealand’s main­land, and rely on in­ten­sive trap­ping and poi­son­ing.

For now, the only method avail­able for large-scale preda­tor con­trol is drop­ping 1080 from he­li­copters over re­mote un­pop­u­lated ar­eas of bush. It is highly ef­fec­tive, but it gen­er­ally doesn’t achieve 100% erad­i­ca­tion and preda­tors rein­vade over time – although a trial is planned by Zip to see if a com­plete knock­out can be achieved by en­tic­ing the an­i­mals with two non-toxic pre-feeds fol­lowed by heav­ier sow­ing of the poi­son baits.

“We will be ul­ti­mately the Gala­pa­gos of the world if we can do this.”

The an­ti­co­ag­u­lant brod­i­fa­coum is used in off­shore is­lands to achieve to­tal elim­i­na­tion of rats, but it builds up in the en­vi­ron­ment so can’t be used re­peat­edly and is not per­mit­ted aeri­ally in un­fenced ar­eas on the main­land. A re­cently de­vel­oped poi­son, PAPP (para-amino­pro­pio­phe­none), is an ef­fec­tive and hu­mane killer of stoats and cats, but it is not reg­is­tered for aerial dis­tri­bu­tion over large ar­eas.


In­no­va­tive Wellington com­pany Good Na­ture has de­vel­oped self-re­set­ting traps – but a quick glance at a map of Fiord­land or Kahu­rangi Na­tional Park is a sober­ing re­minder that even such a highly ef­fi­cient trap is no match for the preda­tors that rule our vast back coun­try.

If the war on pests is to be won, new weaponry is es­sen­tial. Some of the lead­ing work to im­prove the ar­moury is be­ing done from a cramped of­fice near Lin­coln Univer­sity by sci­en­tists Elaine Mur­phy, Tim Sjoberg and Tom Agnew of Zip.

They are ex­per­i­ment­ing with an ar­ray of meth­ods that could lead to the de­vel­op­ment of “su­per-lures” that would work as

high-tech Pied Pipers, draw­ing pests from across a wide area to traps. They have dis­cov­ered, for in­stance, that a tiny piece of dacron taken from the bed­ding of a cap­tive stoat will draw other stoats. Other sci­en­tists have found that fe­male pos­sum urine at­tracts other pos­sums.

The sci­en­tific chal­lenge is to iden­tify the volatile com­pounds that make up those smells, then syn­the­sise them cheaply so that they can work as long-life lures in com­bi­na­tion with self-re­set­ting traps.

Smell is just one type of lure un­der in­ves­ti­ga­tion. The Zip team is also study­ing the po­ten­tial of us­ing the pests’ own sounds to draw them to traps. “I have no doubt these guys are all talk­ing to each other right now,” says Sjoberg, as he stands in a seem­ingly silent room full of caged rats kept for an­i­mal-be­hav­iour anal­y­sis. The rodents com­mu­ni­cate con­stantly at an ul­tra­sonic level that’s in­audi­ble to hu­mans, he says.

Be­havioural lures, such as lu­mi­nous 3D ob­jects nailed to trees, are be­ing tested to see whether they will at­tract cu­ri­ous pos­sums. Work­ing in a 2ha fenced en­clo­sure, the sci­en­tists are also ex­plor­ing how light can be used to di­rect or herd rats in a par­tic­u­lar di­rec­tion, and ex­per­i­ment­ing with a small ad­justable preda­tor fence to fig­ure out just how high such a bar­rier needs to be for stoats and rats.

They are also prob­ing the di­etary pref­er­ences of stoats to de­ter­mine the best bait to use with an aeri­ally de­liv­ered PAPP poi­son. It turns out the car­niv­o­rous preda­tors like fresh rab­bit – but to poi­son 100,000ha in this way would take about three tonnes of rab­bit meat, says Mur­phy. “And you just can’t get three tonnes of rab­bit.”


The chal­lenges are as pro­saic as they are com­plex and im­mense. Zip boss Al Bram­ley says much de­pends on im­prov­ing the mon­i­tor­ing of pests in real time so that erad­i­ca­tion ef­forts can be more tar­geted. “At the mo­ment, we are still heav­ily re­liant on some­one go­ing for a big walk to tell you some­thing was there three weeks ago.”

He also sees prom­ise in the po­ten­tial of ar­ti­fi­cial in­tel­li­gence and low-cost ra­dio trans­mit­ters in ef­fi­ciently elim­i­nat­ing preda­tors over big ar­eas.


An­other key line of re­search is the de­vel­op­ment of species-spe­cific tox­ins. “A com­pound that is toxic only to rats, for ex­am­ple, would be a re­ally big break­through,” says An­drea By­rom, head of the Bi­o­log­i­cal Her­itage Na­tional Sci­ence Chal­lenge. “I would say we would get there in two to five years, and that’s huge be­cause it would mean we could ap­ply those tox­ins in places where we can’t right now, like farm­land. It would be a mas­sive op­por­tu­nity to be able to throw out preda­tor baits on farm­land with­out harm­ing dogs and live­stock.”

For those who share a de­sire to see our an­cient bio­di­ver­sity re­stored and made safe from in­vaders, these emerg­ing tech­niques of­fer the tan­talis­ing hope of a more eco­log­i­cally healthy fu­ture. But many ex­perts be­lieve that even these ad­vanced meth­ods won’t be enough, and that achiev­ing a preda­tor-free New Zealand won’t hap­pen with­out the use of fast-emerg­ing gene-edit­ing and gene-drive tech­nolo­gies.

“To think we are go­ing to be­come preda- tor free with­out poi­sons dis­trib­uted from air­craft and/or ge­netic engi­neer­ing could be viewed as overly op­ti­mistic,” says Josh Kemp.

In a coun­try that took ge­netic mod­i­fi­ca­tion off the agenda more than a decade ago, and in which de­ter­mined pock­ets of re­sis­tance re­main to the use of 1080 (de­spite com­pelling ev­i­dence that, for now, it is the sin­gu­lar tool keep­ing species from ex­tinc­tion), the big­gest ob­sta­cle to res­cu­ing kiwi, kokako, kea and their en­demic cousins may not be a lack of money or know-how, but a lack of will.

Next week: how ad­vances in gene tech­nol­ogy could pro­vide a pow­er­ful tool in the war against preda­tors; har­ness­ing ar­ti­fi­cial in­tel­li­gence to pro­tect the birds; and a Wellington man’s am­bi­tious com­mu­nity-ini­ti­ated con­ser­va­tion project.







Some of New Zealand’s threat­ened birds: 1. Kokako. 2. South­ern brown kiwi (tokoeka). 3. Rock wren. 4. Kaka. 5. Takahe. 6. Yel­low­head (mo­hua). 7. Kea.

A pos­sum tuck­ing into fallen fruit. Left, a pos­sum em­bryo in its mother’s pouch.

In­tro­duced preda­tors that are wreak­ing havoc: rats, pos­sums and a stoat at work in na­tive bush. Pho­tographs by Nga Manu Na­ture Images/www.nga­

Abel Tas­man Na­tional Park: over the next 30 years, $25 mil­lion will be spent to re­store its ecol­ogy.

“Su­per-lure” quest: Tim Sjoberg (left), Tom Agnew and the stoat en­clo­sure at Lin­coln Univer­sity.

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