A major pest control programme to stem a rodent plague of "biblical proportions" was announced by Conservation Minister Nick Smith today.

The largest pest control operation ever undertaken in New Zealand, the Government's 'Battle for Our Birds' programme, was announced today in Maruia, after outlining the initiative in January.

It aims to protect native wildlife from the exploding population of rats and stoats, which could trigger the death of millions of native birds over the spring and summer period, Dr Smith said.

"Forest monitoring has confirmed that about a million tonne of seed has dropped in this year's beech mast and that this has triggered a plague of rodents of biblical proportions."


Seven thousand predator tracking tunnels and 430 seed collection trays were monitored for four months by the Department of Conservation, during which the rat population grew fivefold from three million to 15 million, and projected to reach 30 million.

Stoat numbers, which pose greater threat to native birds, are estimated to grow to 25,000.

The operation, which will span 29 forests and 700,000 hectares, would involve the use of toxins such as the controversial 1080, but Dr Smith said the science had to be backed.

"Pre-feeding, improving bait quality to avoid crumbs attractive to birds, helicopter rather than fixed-wing aircraft distribution, GPS, and the development of repellents for non-target species have enabled major improvements in 1080 control methods."

The operation will cost $9m-12m and will be extended to cover one million hectares by the end of the year.