An enormous effort to save native birds from a tide of pests has delivered some promising results in the South Island, following 1080 drops across vast swathes of beech forest.

Despite rat populations reaching plague levels in some areas - on the back of a one-in-15-year beech seeding event last spring - tracking rates indicate rats and stoats were knocked down to undetectable or very low levels at most sites, giving much needed protection to vulnerable native birds and bats.

Over the past eight months, the Department of Conservation has treated more than 600,000 hectares of priority conservation areas using aerial 1080 drops to control rats, possums and stoats as part of its coordinated programme dubbed the Battle for Our Birds.

When announced in 2013, the $21 million project was aimed at combating the seeding event, fuelling pest populations with surplus food, with a goal of protecting 25 million native birds a year over the next five years.

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Along with 1080, poison bait stations and expanded trapping networks have also been used against a population boom of millions of rats and thousands of stoats.

"Rat levels crashed in most areas and tracking indicates we've also knocked back the stoat plague that often follows these beech mast events," DOC Deputy Director general conservation services Mike Slater said.

"It'll take another breeding season to assess the full impacts but we're already starting to see positive breeding results for some of the native birds and bats we're watching closely."

Early results showed the nesting success of rock wren, mohua, robin and riflemen was significantly higher in areas treated with aerial 1080 than those without.

In particular, rock wren nesting success in a drop area in the Kahurangi National Park was 85 per cent, compared to 30 per cent in nearby areas without pest control.

"Whio/blue duck and bats also look to have benefited although we don't yet have the final results from these monitoring programmes," Mr Slater said.

However, some native birds had also been lost to 1080 through the pest control operations, including four out of 48 kea tracked at sites in South Westland, Kahurangi National Park, Arthur's Pass National Park and at Lake Rotoiti.

"It's unfortunate to lose any kea but without protection most kea chicks are killed by stoats so the overall benefits of these operations outweigh individual losses."

Earlier, anti-1080 campaigners had claimed more than 20 rock wren at a research site at Kahurangi National Park had been wiped out by the poison, but DOC said today there was still no evidence as to why the birds went missing unseasonable weather and snow and the pest control operation last spring.

While some birds were probably lost to 1080, early counts indicated the high nesting success due to stoat control had already balanced this out with 61 birds estimated in the area after the operation was carried out, compared with 49 birds before hand, DOC said.

The full effects of aerial 1080 pest control on rock wren would not be known until the end of next summer when the birds had another chance of breeding with reduced stoat numbers.

Rat populations had meanwhile reached extreme levels at some sites and there were lower knock down rates than expected in a small number of operations although rat numbers still plummeted.

"We are closely analysing results so we can pinpoint the factors such as timing and sowing rates that we could improve in future predator plague responses."

DOC is planning to carry out aerial 1080 pest control over about 250,000 hectares this year - about 50,000 hectares more than normal - to protect vulnerable native species from pests.

"We are not expecting another beech mast this year but the Battle for Our Birds continues and DOC is committed to extending our regular pest control work to protect our most at-risk native animals and plants."

Conservation Minister Maggie Barry said the programme had shown how important 1080 was in protecting native creatures.

"Bird breeding success rates in areas which were targeted are also considerably higher than where there were no drops," Ms Barry said.

"For example, the nesting success for the threatened mohua/yellowhead in the Dart and Routeburn Valleys this summer was just under 100 per cent, where previously almost half these nests have failed to produce eggs or chicks which survived."

The Battle for our Birds

•The Department of Conservation's 2014/2015 Battle for our Birds pest control programme was targeted to combat a seed-fuelled plague of rodents and stoats across large areas of South Island beech forests. Operations were designed to protect at-risk populations of mohua/yellowhead, kakariki/parakeet, kiwi, whio/blue duck, kea, kaka, rock wren, giant land snails and native bats.

•DOC monitors rat numbers using tracking tunnels before and after pest control operations to show their success and results are shown in the attached graph.

•Stoats are only monitored once a year after they breed in the summer. Results from stoat tracking show stoat plagues were prevented at all 15 sites analysed to date.

•DOC is continuing to closely monitor key at-risk native bird and bat species (mohua, whio, long-tailed bats, rock wren and kea) at a number of sites to gauge the on-going effects of pest control.