What if we do NOTHING?
The case for the prudent use of toxins in mamalian pest control
by Jude Gilbert and John Ogden


The film on 1080 by the Graf brothers recently shown at the Tryphena Club to around 35 people made compelling viewing. It was a well-crafted document showing the purported serious levels of by-kill and contamination of water and food sources from 1080 aerially dropped into catchments on the DoC estate on the mainland.
The film had a strong deer hunting perspective; but at no time did it mention why this style of pest management was started, or why this particular toxin was chosen. In the first half of the twentieth century red deer ravaged the mountain forests and sub-alpine grasslands throughout both islands. As early as 1924 the newly formed Native Bird Protection Society said: “Deer, introduced and fostered for the pleasure of an infinitesimal minority, have committed many thousands of pounds worth of damage to our indigenous forests”, and by 1935 the Legislative Council was advising Government that it “should take active and effective steps to exterminate the deer and wild goats which are doing irreparable damage to our native forests, many of which, if not more seriously protected, will inevitably be destroyed”. As predicted, vegetation loss led to increased erosion in the hills and flooding in the lowlands. By the 1950s animal control was taking place throughout the mountainous areas of the country, but deer numbers did not decline until the advent of helicopter hunting 1960s. By then it was too late for many plant species to regain their former abundance. None of this history, or the clear scientific and photographic evidence showing the detrimental effects of deer on native forest ecosystems, was even mentioned in the film.
Deer and possums (and all other herbivorous mammals) were introduced to New Zealand. Our forest ecosystems, co-evolved with birds over millennia, had never experienced teeth and hooves. The introduced mammals had never had such an abundant and succulent food supply, free from their normal predators and diseases, and increased exponentially. Their effects were drastic and are still going on. For example, in the Kauaeranga Valley (behind Thames), possums and goats have totally eliminated fuchsia, kohekohe and northern rata from study plots set up in the 1980s. These species are key food sources for native bellbirds, tui, kereru and kaka. The majestic tall, tiered forest is being reduced to tree-fern scrub. Many other examples could be given. To suggest, as the film did at one point, that possums might be beneficial to the bush, flies in the face of abundant evidence to the contrary.
The film’s rebuttal of DOCs evidence of the beneficial effects of 1080 relied on the apparently sober testimony of one Dr Q. Whiting O’Keefe. Dr O’Keefe (with an American medical background) criticised the research of Ralph Powlesland, Rod Hay, Eric Spurr, John Innes and several other New Zealand ecologists with lifetimes of experience in forest ecosystem research. Quotes were taken out of context in some cases, and research was criticized for lack of randomization and replication. The reality, when attempting to save the last few survivors of a species and faced with clear numerical evidence of imminent extinction, is that these ideals of scientific methodology can rarely be applied. Knowingly and reluctantly they were sometimes set aside in favour of a last-ditch trial and error approach called “research by management”. This was not done without an understanding of its limitations, and results were all recorded carefully, and often monitored over many years. Had this not been the case, Dr O’Keefe would have had nothing to criticize. The Department of Conservation has indeed sometimes had to make difficult management decisions based on limited or possibly confounded data, and no doubt some errors have occurred. But to suggest that many kiwi scientists, all with training and commitment to New Zealand conservation, would willingly misrepresent their results is, quite simply, incredible. One of the glaring inconsistencies in the film was that the ‘evidence’ it presented verbally and visually was not backed up by the same rigorous science that was demanded of DoC.
On Great Barrier 1080 is not an issue; it is simply not used here as we have no red deer or possums. The decline of the biodiversity on this island lies with the historical loss of habitat from forest burning and clearing, the subsequent loss of food sources, and the introduction of weeds and mammalian pests. The island has lost twelve bird species, probably fifteen plant species, two reptiles and an unknown number of terrestrial snail and insect species since the arrival of Europeans and ship rats.
It is estimated that there are 8 rats per hectare in forest and up to 30 per hectare in grassy habitats close to dwellings, giving a grand total of c. 286,000 for the island as a whole. . At Windy Hill over 9 years of trapping some 30,000 were caught! The impact on seeds, seedlings, invertebrates, lizards and birds, night after night, year after year, decade after decade, is immense. This only becomes obvious where species become extinct or are hanging on in tiny numbers.
The measuring of the densities of species, from birds to lizards, is exacting work and the trends can only be seen after many of years of accumulating data – monitoring. Despite the opposite claim in the film, there are several cases of carefully monitored species populations in New Zealand – indeed the film actually showed data from one such programme – kokako at Mapara. The problem on Great Barrier is that we do not have enough people counting. The GBI Trust, Glenfern and Windy Hill Sanctuaries all have ongoing multi-species monitoring programmes and these are beginning to paint some pictures. Levels of species present are now known, so that improvements (or otherwise) can be judged. And that is the point missed by O’Keefe – this sort of data is rarely definitive – judgement is required.
Of the 28,500 hectares that make up Great Barrier island and its many islets, only around 1500 hectares (c. 5%) is managed in any integrated way for pests and weeds with the aim of halting the waning of the biodiversity. The Mohanga Peninsula, Motu Kaikoura, the Okiwi School project, and the Sanctuaries at Windy Hill/Rosalie Bay and Glenfern all have a biodiversity focus – that is they are aiming to give all native species a much better opportunity to thrive in the absence of, or with low densities of, pests. The Department of Conservation, on the other hand, with its appallingly small budget for biodiversity, is mainly single species focused, such as the management of cats in relation to pateke in the Okiwi basin. The rest of the DoC estate, more than 60% of the island, has no active protection from mammalian predators at all. So rats, feral cats, and pigs feast at will in the extensive northern forests of Hirakimata and Te Paparahi.
People often make the comment that we only need to have more trees to improve the situation for birds. But the dynamic in the bush is driven by food – the more food there is for birds, the more there is also for the rats, feral cats, and pigs to eat. Rats are highly tuned to food availability and can respond much more quickly to increased food abundance than other species by breeding more frequently and having larger litters. The composition of the bush on the island is also changing as it recovers from former clearance. At Windy Hill when the land was purchased in 1972 it was estimated that there were about 100 acres of grass, now there are about 4 acres. Over 37 years manuka and kanuka have reclaimed the open spaces. Elsewhere on the land the more mature kanuka are giving way to the wide range of plant species that succeed it – it is a constant process of change until mature bush dominates creating better food abundance, particularly for the larger birds like kereru and kaka. It is believed that there is already sufficient food available to support much higher densities of birds throughout the year than exist currently, but poor breeding success due to the predation by rats keeps bird numbers low. This will be replicated for many other species, like lizards, too.
The North Island robin at Windy Hill provides us with graphic examples of breeding success and failure in an area where rats are kept at low numbers. Each season every nest, some 40 of them, is watched from the time the eggs are laid until the baby birds are banded just before they fledge. Every year, despite additional protection around the nest site, nests are predated by rats at all stages – eggs, chicks, and occasionally the female adult as well. It only takes one rat! Fortunately, with the toxin and trapping regime in place, over 80% survive to fledge and leave the nest. We can take these results as indicative for the success of other small bird species like silvereye and fantail in this intensively managed area, though, as O’Keefe would insist, we can’t prove that is the case!
Elsewhere, in the unmanaged bush; carnage! Night monitoring of fantail nests has demonstrated that about 95% of nests are predated by rats. Small birds, such as fantails, survive only because they are such prolific breeders. The most effective anti-rat tool we have currently, with all its recognised risks, is Brodifacoum – the active ingredient in Talon and Pest-Off rat baits, commonly used by many households on island. It is known as a “second generation anticoagulant” and has been used successfully in aerial drops on Hauturu, Cuvier, and Tiritiri Matangi to name a few. These islands are now burgeoning with native species and are used as a species source for translocations to other areas.
Clearly accidental poisoning of horses, stock, dogs and other pets is unacceptable. How frequently such ‘mistakes’ occur we couldn’t judge from the evidence presented in the film. But no-one takes the use of a poison lightly – all toxins come with risk and the balancing act for those of us using Brodifacoum on a biggish scale, is to measure the risk- benefit equation as carefully as we can. At Windy Hill it was only after six years of trapping (without toxins), when monitoring showed that 30% of tracking tunnels still showed evidence of rats, that the decision to introduce a toxin to the programme was made. Over the last year the programme has converted to a toxin base with back-up trapping and we are achieving the best results in terms of measured low rat densities in ten years.
What is clear is that the state of our biodiversity is the best indicator of the health of our ecosystems. Ecosystems provide us with the elements that sustain life – the “services” of clean water, soil regeneration and stability, air purification and carbon sequestration, pollination, and nutrient cycles. Ultimately these terrestrial processes can also influence fish stocks, and other resources from the ocean. We all agree that we do not want to risk poisoning them, and we need good science to re-assure us that poison residues are indeed being degraded and not slowly accumulating.
If we do NOTHING to actively conserve and protect the ecosystems on this island and the native species that live in them, then we impact on those very things that sustain a quality life. We already have a much improved quality of life here than if we lived in, say, Auckland. Unfortunately the birds, lizards, invertebrates, and other species are still at risk here. The rate of extinctions on Great Barrier is probably continuing at the same rate as everywhere else in NZ, but starting from a smaller initial number. Currently, there remains a tiny handful of tomtits and only slightly more kakariki but without protection these too will slowly go as have the bellbirds, saddleback, stitchbird, rifleman, and kokako.
Only we can improve their lot and to do so we have to make informed choices based on sound science, balance the risks and benefits of whatever methods we choose conscientiously, and tread carefully as we go. If we are to make any difference to the plight of the planet it starts here, at home creating a quality habitat for our native species.