Aerial 1080 poison drops planned to help Whanganui region's wildlife

Kiwi numbers in the Whanganui National Park and Waitotara Conservation Area are in a slow decline. Photo / NZME

Three aerial 1080 operations in the Whanganui region will make for healthier native forests with more birds, Predator Free 2050 landscape manager Peter Morton says.

The Department of Conservation (DoC) plans three major aerial 1080 poison bait operations for the 2021 to 2022 year.

The drops are for the 10,700ha Erua Wetland west of State Highway 4 near National Park, the 22,000ha Tongariro Forest west of the central North Island volcanoes and the 50,700ha of sprawling forested hills in the Whanganui National Park/Waitōtara Conservation Area.

The Erua Wetland operation was completed at the end of July. The drop was targeted at protecting North Island brown kiwi, New Zealand falcon, whio (blue ducks) and long tailed bats.

After the operation the rat population, previously at 15 per cent bite mark index (BMI), went down to 0.

However, the other drops could not take place under level 4 Covid-19 restrictions.

With the drop in alert level, the Tongariro Forest and Whanganui/Waitōtara drops will also need settled weather and permissions, including from public health officials.

Surrounding landowners and user groups will be consulted first through written information, meetings and phone calls.

In the Tongariro Forest whio numbers have increased dramatically in more than a decade of predator control, but North Island brown kiwi chicks are being consistently killed by ferrets.

"In areas where kiwi are present, detecting mustelids at any level means almost inevitable chick loss and a three-yearly rotation of aerial 1080 is used to provide a window of opportunity for chicks to reach maturity at least in the season immediately following the operation," Morton said.

The 1080 operation aims to allow half the kiwi chicks hatched to reach adulthood, and pairs of whio to raise 1.6 chicks each, provided rivers do not flood.

Over in the large Whanganui National Park/Waiōtara Conservation Area the kiwi population has been in a steady 5 per cent annual decline and possum numbers are at 53 per cent BMI.

The drop there aims to turn the kiwi decline around to a 10 per cent population increase in three years. It's also to protect trees like kamahi and northern rātā from possum browse.

Most of the 1080 poison bait used in New Zealand is manufactured in the Orillion factory in Whanganui.

Orillion chief executive William McCook said he believed a lockdown presented an opportunity for aerial operations.

"There's never been a better chance to get large scale operations undertaken, with the lack of hunters, trampers and recreational people using parks and reserves."

Pest and predator control was essential, he said.

"If New Zealand has periodic outbreaks of Covid in the community then the operators are going to have to think of ways to safely undertake predator control operations."

There are 10 staff working at Orillion at present, in what would have been an average year of production until Covid came along.

Production was ramped up for 2019, a year when beech forest seed production was the highest in 40 years. There were also beech "masts" in 2014, 2016 and 2017. Another is predicted in the coming summer.

The "masts" happen when a summer is significantly hotter than the previous one. The trees produce more seeds, which increases the number of rats and stoats. When they run out of their usual foods they prey on birds.