DOC gearing up for Kahurangi National Park 1080 drop to hit rats

Thursday, 2 May 2019

Areas of Kahurangi National Park with public access will be closed while toxic baits are present. (File photo)

An aerial drop of 1080 is set for a large area of the Kahurangi National Park to control a booming rat population.

This year's beech mast, or heavy seed production, is expected to lead to a heavy breeding season for rats taking advantage of the abundant food source.

DOC Motueka operations manager Chris Golding said the 1080 treatment of 326,000 hectares of the rugged park was building on conservation work in the area, and to counteract the effect of the beech mast.

'The seed will provide more food for rodents, fuelling rapid rises in their numbers. With more rodents to feed on, stoats produce more young and their numbers spike in the summer after a beech mast.

Motueka operations manager biodiversity Chris Golding with a kiwi. Golding said 1080 was the only pest control method that could manage rat and stoat surges in the Kahurangi.

* Pest control in Kahurangi easier than expected**

'The operation is targeting rats, but it also reduces stoats to low numbers through their eating poisoned rodent carcasses.'

He said the aerial application was the best option for the Kahurangi terrain.

'Aerial 1080 predator control is the only pest control method that can be deployed rapidly to manage rat and stoat surges over vast or rugged terrain. Ground control would not be viable over the large area of Kahurangi where predator control is required to protect at-risk native wildlife.'

Rock wren fledglings like these have three to five times the success rate in 1080 treated areas compared to those without 1080, according to DOC.

Kahurangi National Park is home to many vulnerable species including kākā, kea, great spotted kiwi, and rock wren. All are ground-nesting birds which are particularly prone to rat and stoat attacks.

The rise in rat numbers coincides with the breeding season for many birds. Golding said DOC monitoring of rock wren nesting in the area showed 1080 vastly increased breeding effectiveness.

'Rock wren raised three times more chicks the year after aerial 1080 than birds in a non-treatment area. The next season they raised five times more chicks than the comparison area.'

He said the population in a 1080-free area dropped from 25 individuals to just two after less than two years. That area has since had aerial 1080 drops and the rock wren population is increasing, he said.

Golding said there was a risk to kea in the area, but said this was offset by the protection for nesting birds.

Kahurangi is home to many kea considered at low risk of 1080 poisoning due to their remote habitat.

'Overall, the kea population is better off after 1080 treatment than without it. If predators are not controlled after a beech mast or seeding event, high stoat levels wipe out most kea nests and kill adult birds too.'

He said DOC had tracked 71 individual kea through several 1080 treatments to multiple sites, and found that two kea were poisoned.

'The loss of these birds is unfortunate, but would have been easily offset by the much better nesting success of the kea population in the park after predator control.

Kea nesting success, where chicks survive to fledge, improved from just 2 per cent between 2009 and 2014, to 50 per cent after the 2014 and 2016 aerial 1080 operations.'

He said kea living in areas close to humans, where they were more used to scrounging human food, were at a 'much higher risk' of 1080 poisoning than kea in remote areas.

'Kea in the remote back country, where most of our aerial 1080 predator control work is done, are at low risk of being poisoned. Feeding kea and allowing them to scavenge our food is not only bad for their health but puts them at greater risk of dying in our predator control operations.'

The aerial drop, from Kahurangi Point down to Owen Valley, will be divided into four treatment blocks, each one being treated with 1.5kg of 1080 bait per hectare.

The treatments will begin from May 6, weather dependent, and will take place between May and December this year. All treatments begin with an initial non-toxic bait pellet treatment, followed at least five days later with toxic pellets.

Areas with public access which are subjected to the aerial 1080 treatment will be closed while bait is in the area, and will be well sign-posted.