It's a delicate ecosystem, with centuries of isolation from land-dwelling mammals making their sudden arrival all the more devastating. The arrival of humans and our pests saw the huia and moa disappear, with the kiwi, the kakapo, the tuatara limping on.
Many of our endemic species can only survive with intensive and concerted efforts at pest control. And that means 1080. We use probably 80 percent of the world's supply of the poison.
Here's why 1080 has become the poison of choice for protecting New Zealand's wildlife from further decline.
What is 1080?
1080 is a poison, with the active ingredient fluoroacetate. In New Zealand we mostly mix it with cereals for dispersal in forests. We do a lot of dispersal by helicopter or plane.
The case for 1080
The Department of Conservation says 1080 works. It's most recently credited the recovery of a rare bat to use of the poison in Fiordland, and puts increasing numbers of rock wren down to the poison too.
Another example of 1080 working is in the central North Island's Tongariro Forest.
Before 1080 was dropped in 2006, kiwi chicks had a less than 25 percent chance of survival to six months. After it was dropped, kiwi chick survival more than doubled to levels that would stabilise the population.
But success is shortlived - stoat populations increased within two years and kiwi chick survival decreased to pre-control levels.
Why do we use SO MUCH OF IT?
There's one thing that makes New Zealand's sets New Zealand's target pests apart from the species we want to protect. The pests are mammals and, aside from two native bats, the species we want to protect are birds.
In most countries, 1080 can't be used effectively because it's attractive to both pests and protected mammalian species. In New Zealand, we can do things to make it less attractive or accessible to native birds. New Zealanders have become pretty good at using 1080.
When we drop 1080, we kill close to 100 percent of rats and possums in the area.
Why don't we just trap the lot?
Trapping is extremely labour-intensive and expensive. Traps have to be constantly checked and reset, and vast swathes of New Zealand's wilderness is inaccessible to humans.
Poison, on the other hand, can kill hundreds of animals in one go.
The combination of the size of the conservation estate and its inaccessibility makes aerial poison control the most practical option.
How do we use 1080?
A 2011 report put together by the independent (AKA not politically aligned) Parliamentary Commissioner for the Environment says aerial 1080 possum control is conducted every 5 to 10 years, whereas for rats, the faster breeding cycle mean they need poisoning every 2 to 4 years.
In between aerial drops, bait stations are typically refilled several times a year.
Doesn't it kill native animals, including lots of kea?
This is almost inevitable. 1080 can kill reptiles, birds, fish and insects as well as introduced mammals like pigs, deer and dogs.
Some of the most heart-breaking stories have been of the deaths of kea following 1080 drops. Between 2008 and 2015, DOC recorded 24 kea deaths caused by 1080 from a population of 199 that were radio tagged.
At the time the figures were revealed, DOC said the benefits still outweigh the accidental by-kill rate.
It's easier to prevent by-kill when 1080 is placed inside bait stations instead of dropped aerially - but it's a much more labour intensive form of pest control not suited to difficult terrain. Most bait used in aerial application in public conservation forests are cereal baits dyed green to discourage birds from eating them.
Mammals are more susceptible to the poison's effects than birds, reptiles or fish. A study that added bait to five streams in 2004 found no effect on fish or insects.
The conclusion from DOC, Forest and Bird and the Parliamentary Commissioner for the Environment is benefits to bird populations following 1080 use far outweigh any accidental bird poisonings.
What about the hideously slow death 1080 causes?
There's no denying death by 1080 is hideous. Possums can take five to 40 hours to die. Dogs, stoats and ferrets may convulse, slow down, become paralysed and struggle to breathe before dying.
One way to make death more humane for target species would be to add painkillers. There are no painkillers added to 1080 in New Zealand.
The National Animal Welfare Advisory Committee rates 1080 as moderately humane. In other words, there are poisons that kill slower and more painfully.
Are we poisoning our soils and waterways? What about my dog?
Dogs can be particularly affected by 1080. They may scavenge the bait itself or eat animals that have been killed by the poison. Regulations mean any 1080 drop needs to be clearly notified, with plenty of signs, but there have been problems where notification was insufficient.
There have been numerous studies of the toxicity of 1080 in New Zealand's soils and waterways. They've found it breaks down especially quickly in water.
1080 can take several months to break down in soil when it's extremely dry and cold. In favourable conditions, it's more like one to two weeks.
Landcare conducted a study using 10 times the number of 1080 baits that would be expected to enter streams. No effect on aquatic life in streams was found.
After aerial 1080 operations, studies found concentrations hundreds of times lower than what would be required to kill an ant in leaf litter.
A child eating just one bait would be seriously harmed. It would take eating 7 baits to kill an adult. That said, there has been one death due to 1080 in New Zealand. In the 1960s, a possum hunter ate 1080 jam bait - which is now banned.
"The case for the use of 1080 is very strong"
1080 is the best option we have, was the conclusion of the landmark 2011 report from the Parliamentary Commissioner for the Environment.
The report concluded:
1. It's an effective way to kill three target species: possums, rats and stoats in one hit. When the predators are targeted en mass together, it gives native species a chance to reproduce for a couple of seasons
2. It's effectively used during beech masts, when pest populations typically boom
3. It's easily applied by air over remote areas, and
4. Is much cheaper than ground control.