A small yellow insect-eating bird with a loud melodious call is what first drew Graeme Elliott into the world of New Zealand's native birds.
Elliott, a self-confessed "nerdy little birdy kid" was raised in Christchurch and spent family holidays in Nelson where he remembers climbing Mt Arthur to look across the huge expanse of Kahurangi National Park, and wonder what was out there.
The Department of Conservation scientist says when he looks out across the second largest national park in the country now, he knows what isn't there.
Elliott paints a bleak picture of indigenous bird life in New Zealand. Without "intensive intervention" he says our native birds will continue to decline until they are extinct.
"I've always thought about the forest and the backcountry as the place where all our native animals lived and yet you realise now you go out into the Kahurangi National Park and you realise they don't live there any more, for the most part they have gone."
When he first began working with native birds in the 1980s, Elliott says there was a general acceptance that the species that were going to become extinct were already on their way out.
However it was the slow decline of species that had gone unnoticed, like the mohua, whio and kiwi that became a growing concern for him.
It all came back to that elusive yellow bird, the mohua, that he had studied during his PhD in the Eglinton Valley in Fiordland National Park.
It was during a stoat plague following a beech mast in the Eglinton Valley that he says the mohua got "slaughtered" which shed light on the reasons for their slow decline.
"Since then I haven't been able to get away from those little buggers," he says.
The Battle for our Birds
The Battle for our Birds campaign was announced by then Conservation Minister Nick Smith in early 2014 as a response to the predicted heavy seedfall from native beech trees, known as a beech mast. The resulting abundance of food was predicted to drive up mice and rat populations, which in turn boosts stoat numbers.
Battle for our Birds was the most most wide-scale drop of 1080 in New Zealand history.
Between August 2014 and February 2015 more than 800 tonnes of 1080 was aerially applied over close to 700,000 hectares of forest in the biggest operation of its kind that had occurred in New Zealand.
Early indications suggest that 2016 will also be another beech mast year and may prompt more large-scale drops.
Barry HarcourtAn endangered mohua, one of the species that the Battle for our Birds is aimed at protecting.
Elliott says the campaign targeted about half a million hectares - more ground than was normally covered, targeted at beech forest.
He says the 1080 "knocked the rats for six", but there were a few sites where it didn't do a good job and the numbers of rats remained high. But he maintains the numbers were significantly less than if 1080 hadn't been used.
He also acknowledges that 1080, deemed controversial by some, would have killed native birds, but argues that many more would have been killed by rats and stoats if it weren't for the use of the poison.
Commonly quoted figures from DOC show 95 per cent of rats and 85 per cent of stoats were wiped out following the operation.
When it comes to the use of 1080, or sodium fluoroacetate, for predator control, Elliott says there have been some significant developments in the use of the poison within the last decade.
The approach was relatively new. Before 2000, DOC had not used 1080 to control rats and stoats following a beech mast. Scientists had only recently discovered that aerially applied 1080 also killed stoats, who were not attracted to the pellets but would die from eating poisoned rodents through scavenging.
Then in 2005, Elliott says they discovered that pre-feeding by dropping baits without poison, reliably killed a higher percentage of rats as it prevented them from becoming bait-shy.
His interest in 1080 came about as it was an effective tool that could be used across large tracts of back country, as opposed to labour intensive methods like trapping.
"It's a funny business, everybody expects us to know how to do it and they sort of say if you can't do it perfectly you shouldn't be doing it," he says.
"How are you supposed to find out how to do it perfectly? There is a lot of learning to do before we will get these operations perfect."
However a vocal opponent of 1080, Bill Wallace, says DOC's figures do not show that the aerial 1080 operations as part of the Battle for our Birds were a success, he says a different approach is needed.
Wallace, founder of the Ban 1080 party and a mussel farmer in Golden Bay, says he was interested in how the pest control operation would be carried out, particularly in the Kahurangi National Park.
"I did an ecology degree many years ago, I wanted to read the science myself and the more I read the more concerned I became," he says.
Wallace has filed several Official Information Act requests on the results of the Battle for our Birds operations and believes the reported numbers have been manipulated.
When he asked for the mice and stoat monitoring results in the Kahurangi National Park before and after the aerial 1080 operation he was surprised to find there was no data available from before the drop because the stoat population had not been measured in 2014.
"How there can be an 85 per cent reduction in the number of stoats when there were no stoat tracking devices in the Kahurangi National Park?" he says. "It is real shonky science."
Wallace says he is no expert, but having examined the rodent tracking data received from DOC in the Kahurangi National Park he believes the drop in rat numbers is more like 67 per cent than the 95 per cent reported.
"It is interesting in the 2015 figures there is generally about a natural 50 per cent reduction in rat numbers because of winter conditions, so how much was really achieved with the Battle for the Birds" he says.
Of particular concern were the 39 monitored rock wren, 25 of which remain unaccounted for in the Grange range of the Tasman Wilderness Area in Kahurangi National Park, which was subject to a 1080 drop for the first time in October 2014.
Rachael KellyA Jet Ranger lifts a 300kg trickle bucket full of cereal baits laced with 1080 at Piano Flat in Northern Southland.
Wallace says the loss of the rock wren was an "unnecessary ecological disaster" as the small birds live in an alpine habitat where there were no rats recorded by DOC.
Ad FeedbackDuring the 2014 operations, four monitored kea were also killed by 1080.
Wallace says it wasn't just four kea, it was four kea wearing radio transmitters, 10 per cent of the radio tagged kea meaning the total figure was much higher.
Four monitored kea were killed during 1080 operations in 2014.
Wallace says DOC's own science warned against exposing endangered birds to 1080 until mortality could be established at less than 3 per cent and it appeared that wasn't the case.
The former helicopter pilot used to fly DOC workers, trout fisherman and sometimes hunters into the Kahurangi National Park and argues that if people can be flown into the back country to find tracking tunnels without tracks, they could just as easily deploy and maintain self setting traps in certain areas.
While trapping the vast back country was not viable, targeting specific areas where rats are known to be in high densities was an option.
"Their science proved the rats were in the river valleys, why not prioritise a river valley each year and put a thousand traps in?" What I'm proposing isn't ever going to eradicate them but neither is 1080, [DOC] know that."
It seems the future of conservation and pest control in New Zealand involves the use of several tools in the battle to protect our native wildlife and maintain biodiversity.
Having studied the toxicology of poisons used for pest control over the last 25 years, Charles Eason says 1080 remains a valuable tool that will continue to be used to control pests.
The professor of wildlife management at Lincoln University says pest species remain a huge challenge in retaining native biodiversity in New Zealand.
"It is a matter of integrating the use of 1080 with other tools to maximise that benefit and keep the pest populations down."
Eason says the future involves thinking of new strategies as well as developing new ways to use existing tools, combining the use of poison with other tools, like resetting traps and toxin delivery devices.
In the last 10 years, Eason says there have been significant developments in how the poison is used and work had been done to improve its effectiveness with research showing it was possible to have a higher per cent kill using less poison.
Research was being undertaken to develop lures and repellents which would make the poison more targeted, he says.
"There have been lots of attempts to make advances in this field and I kind of refer to it as a pipeline of technology."
One of those emerging technologies is the resetting toxin delivery device which sprays poison onto the stomach of an animal as it passes through a tunnel which is then licked off during grooming and leads to the ingestion of a lethal dose.
"You can imagine these resetting devices covering a larger and larger number of areas of the landscape and extending the amount of ground control you can do," he says.
"At the end of the day, aren't we all trying to save native wildlife from pests?"