DOC Westport conservation services manager Bob Dickson said research indicated tracking levels would reach 100 per cent in parts of the park in November, without pest control.
He said more rats also meant more food for stoats, causing their numbers to explode in summer.
"We can't let Kahurangi's vulnerable native species suffer heavy losses from this growing predator onslaught."
DOC planned aerial 1080 drops over about 270,000 hectares in the western, northern and eastern parts of the park this spring as part of its Battle for our Birds programme. The drops would begin in coming weeks, when weather conditions allowed.
"We are particularly concerned to safeguard threatened populations of whio, great spotted kiwi, kea, kaka, rock wren, long-tailed bats and Powelliphanta snails (giant snails)."
Mr Dickson said aerial application of cereal baits containing biodegradable 1080 pesticide enabled large-scale protection in difficult terrain. It rapidly knocked down rats to near zero levels. Stoat numbers also substantially reduced through their eating poisoned rodent carcasses.
The Kahurangi aerial 1080 pest control would also reduce the number of possum, which caused browsing damage to native vegetation and also preyed on native birds, their eggs and native snails.
The Kahurangi operation was one of 25 confirmed Battle for our Birds operations using aerially applied 1080 over about 680,000 hectares of South Island beech forests, Mr Dickson said.
With plentiful food, rats can produce litters of five to eight pups every six weeks. The pups start breeding at 12 weeks old.
Stoats breed only once a year but breed particularly well during a beech mast and produce 10 to 14 kits in spring. As a result, stoats can undergo a five to seven-fold population increase in summer when the young stoats emerge from dens.
- Westport News
