Rat population threatens native wildlife - DOC

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A population explosion of rats in New Zealand's second largest national park poses a major threat to native wildlife, says the Department of Conservation.

Kahurangi National Park is one of the newest parks to be gazetted and is in the northwest of the South Island.

Between May and August, rat tracking levels in the park rose from 54 per cent to 90 per cent in the Fyfe River area, from 31 per cent to 51 per cent in the Cobb Valley, from 43 per cent to 78 per cent in the Waingaro River area and from 34 to 63 per cent in the Oparara Basin.

Rat tracking shows the percentage of baited tracking tunnels entered by rats over one night within a monitoring site.

DOC blamed the population explosion on an exceptionally heavy beech seed fall -- known as a mast -- providing abundant food.

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