More than $20 million and 720,000ha: today is D-Day for the biggest pest control operation in New Zealand's history.

At Bobs Cove near Queenstown this morning, Conservation Minister Maggie Barry launched the next major stage of the Government's ongoing "Battle for our Birds", announcing that extra sites may also be targeted for the aerial 1080 offensive.

It's in response to another heavy beech seedfall or mast event, which is triggered by climatic conditions. The sudden abundance of food creates explosions in rat populations.

This also leads to a rapid increase in stoat numbers, further threatening native wildlife in forests.


Although it's unknown exactly what the scale of beefed-up pest populations would be after big beech seeding, scientists estimate numbers can reach in the tens of millions across our forests.

Rats can breed every two months and produce six or more young each time - an 20-fold increase in just eight months.

The 19 sites selected for the operation are in Fiordland, Otago, South Westland, North Canterbury, Kahurangi, the lower North Island, Taranaki and Tongariro, which are home to remaining populations of a number of endangered species.

These include kiwi, kaka, kea, whio/blue duck, mohua/yellowhead, kakaraki/orange-fronted parakeet, rock wren, long and short-tailed bats and giant snails.

The Government committed $20.7m in its 2016 Budget for the operation, which may also involve 1080 drops over an additional 10 sites, spanning about 200,000ha of bush, if pest numbers reach levels that threaten native species.

The first operation, in Kahurangi National Park, is expected to get under way next week and drops will continue through the winter, Barry said.

These would be backed up with expanded trapping networks, including deployment of newly operational self-resetting traps, which significantly increased the efficiency of a network.

The last heavy beech seeding response, Battle for our Birds 2014, which covered 690,000ha, had big benefits for native birds.

In the South Island, mohua in the Dart and Routeburn valleys raised on average double the number of chicks after 1080 treatment than in areas it wasn't used.

The summer after the operation resulted in 89 per cent of mohua nests producing chicks and 97 per cent of adults surviving.

For kea, rock wren and rifleman, improved nesting was measured over the second summer after pest control, showing ongoing benefit.

Both bat species did well and bat numbers increased.

Past monitoring had also shown significant benefits for kiwi and whio/blue duck.

More common forest birds also benefitted - South Island robins raise seven times the number of chicks after 1080 pest control than in areas where predators have not been controlled.

Improved nesting success continued in the pest control areas the following year, showing ongoing benefit for these species, Barry said.

"If we didn't use 1080 to knock down predator populations many precious taonga native species would be extinct by now. It really is that simple.

"We will not back away from using 1080 at this stage - we can't ignore the science and stand by while our treasured native species are hit by another predator plague pushing them into further decline and possible extinction."