Sheep and cute clapboard farmhouses aside, a few other (more unusual) things grab your attention if you happen to be road-tripping across the New Zealand countryside. There’s the surprising non-abundance of birds (this is, after all, a place where the native fauna is very much of the avian variety – so where are they?). And then, of course, there are all the dead possums. 

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Unless you’re familiar with New Zealand’s unique environmental woes, it can be hard to imagine how closely linked these two things are. Since their introduction in the country in the 1850s (to establish a fur industry), brushtailed possums (Trichosurus vulpecula) have become an invading force to be reckoned with. Without any natural predators to hinder their march of progress, possums began breeding with all the fervour their marsupial genes could muster, wiping out the country's beloved birds along the way. About 70 million are now spread out over more than 90% of the landscape. If kiwis, keas and kakapos are few and far between, it's likely because a hungry possum has eaten all their food, gobbled up their eggs and feasted on their newborn chicks.*

So what does a nation of passionate bird lovers do when faced with a furry plague of this magnitude (one that could potentially wipe out the very emblem of its national identity – the kiwi)? It wages war. Bird sanctuaries have been ringed with pest-proof fences, hunting possums is a growing industry, traps deliver piston blows to the head and drivers have been known to swerve whenever a possum dares to cross the road. Even school kids take part in the onslaught with possum-throwing contests and postmortem possum dress-ups.

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But the battle-ax of choice in this war on invasives is 1080 – or sodium monofluoroacetate. Lethal nuggets of cereal and carrot laced with the poison are placed in bait stations or airdropped over target areas for unsuspecting possums to ingest. On the surface, 1080 does appear to be the perfect possum control: it’s relatively cheap, allegedly biodegradable and highly effective against mammals (making it pretty ideal for use in a country with many mammal invasives and only two native mammal species). 

But flip the coin and there’s a darker side. For a start, death by 1080 is not very humane. According to studies on captive possums, it takes on average around 11 hours – and there are uncontrollable muscle spasms, hyperactivity, vomiting, multi-system failure and brain damage somewhere in between. Hated as they may be, perhaps possums deserve a little better? And that’s just the start. A poison that kills mammals like possums will also kill mammals like pets and people – and 1080 detractors say animals outside the mammalian family may also be at risk. Some claim the poison does not biodegrade harmlessly at all, but persists in the water and soil, causing as yet unstudied harm to native species, including endangered frogs and the New Zealand falcon.

Whichever side of 1080 controversy you’re on, one thing seems certain: without measures to control possums, New Zealand’s dwindling bird populations stand little chance of recovery. But perhaps it’s time for a savvier, smarter approach? Developed in the 1940s, 1080 (like the origins of the possum problem itself) seems to belong in a bygone era  … maybe what’s needed to turn the pipe dream of a Pest-Free New Zealand into reality is a uniquely 21st-century solution?

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That solution could come in the form of specially concocted (and possum-specific) contraception. It’s not a new idea – even New York’s subway rats are having a go. The ideal fertility vaccine would slash the possum reproductive rate, possibly by disrupting one of the stages of the fertilization process – but it would also need to be cheap, potent and safe. New Zealand’s researchers have been trying for over a decade to find that silver biocontrol bullet … but they need some serious funding: according to 2011 figures, New Zealand spends around $100 million a year on 1080 operations and less than $2 million on developing alternatives. With my possum empathy burning strong (and the swell of 1080 opposition building), let's hope scientific innovation prevails.