1080 and the risk to non-target species

In 2017, New Zealand’s Biological Heritage National Science Challenge surveyed 8,000 people about pest control, and 84% agreed that pests are a significant conservation problem. However, there is less agreement about methods of pest control. One concern people have about 1080 is the risk of harm to non-target species – species that are not the intended victims of the poison.

Historical uses of 1080

In New Zealand, the poison 1080 is used to control pest species like possums, rats, ferrets and stoats. Aerial 1080 operations began in New Zealand in 1956. The Forest Service, which preceded the Department of Conservation, used fixed-wing aircraft to apply cereal baits at 20 kilograms per hectare (kg/ha) and carrot baits at up to 32 kg/ha. The baits had raspberry flavour added to attract animals. Small pieces, called chaff, broke off the cereal and carrot baits. They were appealing to birds as well as possums and deer.

The 2011 report Evaluating the use of 1080: Predators, poisons and silent forests states that “individuals from 19 species of native birds and 13 species of introduced birds have been found dead after aerial 1080 drops. Most of these recorded bird deaths were associated with only four operations 35 years ago that used poor quality carrot baits with many small fragments.”

Changes to 1080 baits and practices

Public concern about the risk of bykill have led to improvements in 1080 pest control practices. Carrot baits are rarely used in aerial operations, except for rabbit control in open country. The bait size is too large for most non-target species, and baits are sieved to remove chaff. Cereal baits now have cinnamon oil added to attract possums but repel birds. They are also dyed a bluish-green – green to camouflage the bait with just enough blue to discourage birds, who prefer red or yellow-coloured food items. Deer repellent can also be added.

Non-toxic baits are spread prior to an aerial 1080 operation. Pests, especially possums, nibble the new food, find it safe to eat and then seek out the poisoned bait when it is dropped a few days later. This results in a more successful kill rate and means longer times between operations.

Application rates have also changed, with up to 80% less bait used per hectare. Aerial operations now use between 1–2 kg of bait/ha (about 3 grams or less of 1080 poison/ha). Fewer baits per hectare mean that non-target species are less likely to come in contact with a 1080 bait.

Technology has also helped to limit risk to non-target species. Aircraft now use GPS to ensure the accuracy of the application. GPS track lines and boundaries show pilots exactly where to fly. The systems also record flight movements to the nearest metre and where bait buckets are opened and closed.

The gains outweigh the losses

The Department of Conservation (DOC) notes that 1080 is far less toxic to birds than mammals, but some native birds – weka, robins, tomtits and kea – are susceptible. About 12% of radio-tagged kea have died after aerial 1080 operations (Hansford, 2016). Kea that live near ski fields or huts regard many things as food – they are curious, and often get handouts from humans. DOC is testing kea repellents, and care is taken to avoid placing baits above the tree line on mountains.

For some species – the kiwis, riflemen, mohua, morepork, kaka and long-tailed bats – the results are very straight-forward: no animals are killed by the poison and productivity and survivorship goes up following 1080 use. For a few species – weka, kea, robin, fernbird – some animals are killed but the losses are far outweighed by the gains.

Dr Graeme Elliot, Department of Conservation

The dilemma with dogs

1080 residue lingers in dead possums, rats and deer, especially in cold temperatures. This is beneficial for controlling stoats. They are carnivores so they do not eat the baits but die from secondary poisoning – by eating animals that died after eating 1080.

Secondary poisoning causes risks for dog owners. Hundreds of dog deaths have been reported since 1960. Sometimes sick possums stagger onto private property or their carcasses are washed down river from an aerial operation. Many deaths also result from dogs entering operational areas.

I have frequently wished that dogs could read because there would be fewer dog deaths. It’s frustrating when people have clearly ignored signs and taken dogs into operational areas.

Cheryl Brunton, West Coast Medical Officer of Health, as reported in Protecting Paradise (Hansford, 2016).

Other non-target species

Several studies have investigated 1080 and non-target species:

• Reptiles, frogs and fish are susceptible to 1080 but much less sensitive than mammals. For example, it would require three dissolved 1080 baits per litre of water to kill a trout (see The chemistry of 1080).
• Cereal baits were added to five streams at the highest concentration found after an aerial operation. There were no effects seen in before-and-after studies on populations of longfin eels, kōura, upland bullies and stream invertebrates (Wright, 2011).
• Field trials show that some insects are attracted to baits, and insect numbers within 20 cm of baits may fall for a few days. Other trials have shown no evidence of harm (Wright, 2011).
• Wild deer are sometimes killed by 1080. Deer repellent is used in the baits in popular hunting areas, but 1080 is not used over the majority of the country where deer live (Wright, 2011).
• 1080 residues have never been recorded in public drinking-water supplies (Wright, 2011). See the article 1080 and water quality for more information on this topic.

Human error and non-compliance mean that there will be risks of bykill to non-target species. But as Dr Jan Wright, former Parliamentary Commission for the Environment said, “Without 1080, our ability protect many of our native plants and animals would be lost. Keeping bovine TB at bay and protecting plantation forests would be much more difficult and expensive.”

References

Hansford, D. (2016). Protecting Paradise. Nelson, New Zealand: Potton & Burton.

Wright, J. (2011). Evaluating the use of 1080: Predators, poisons and silent forests. Wellington, New Zealand: Parliamentary Commissioner for the Environment. Originally retrieved from https://www.pce.parliament.nz/media/1689/pce-1080-2017-web.pdf, now access from https://pce.parliament.nz/publications/evaluating-the-use-of-1080-predators-poisons-and-silent-forests.