A Northland trial of an automated rat and possum trap has been such a success a group working to rid Ōpua Forest of pests is now considering re-introducing rare native birds and kauri snails.

The
year-long field trial by Bay Bush Action used more than 500 AT220 traps made by NZ AutoTraps of Whakatāne.

Group founder Brad Windust said the self-setting, battery-powered traps had reduced possums and rats to “near undetectable” levels across 260ha of bush south of Paihia.

The group had been unsure how effective the high-tech traps would be against rats but the results had been better even than they’d hoped.

Outside the trial area rats were rife, with up to 71 per cent of tracking tunnels showing signs of the rodents every night monitoring was carried out.

Inside the trapped area, however, rats often went undetected in any of the 60 tracking tunnels used.

On average two traps were installed for every hectare of bush in an effort to get a trap in every rat’s territory.

Possums had also taken “a massive hit”, Windust said.

Possum numbers were gauged by placing wax tags in the trees and counting how many had been chewed three nights later.

Before the trial 94 per cent of tags were chewed; a year after the traps were installed the “bite mark index” dropped to just 5.7 per cent.

Over the same period, the presence of wētā in tracking tunnels jumped from 0 to 55 per cent.

Wētā were an important food source for kiwi but were vulnerable to predators such as rats, Windust said.

A cloud-based IT solution invented by Bay Bush Action co-founder Craig Salmon was used to manage data collected during the trial.

Salmon also developed an app forest workers could use offline when they were out of cellphone coverage, with the data synced back to the cloud at the end of each day.

The $350,000 cost of the project, dubbed Ngahere Ora, was covered by DoC’s Community Fund, Foundation North and individual donors.

Windust said some weaknesses of the traps became evident during the trial.

Some base plates, for example, failed mid-trial because they couldn’t withstand the powerful action of the killing arm.

There were also problems with the liquid lure, which is used to automatically re-bait the traps, congealing and blocking the dispenser.

As a result the group embarked on an in-situ upgrade programme with support from NZ AutoTraps.

The newest version of the trap was better able to stand up to the rigours of the job, he said.

Bay Bush Action had produced a report detailing its findings and hoped it would prove useful to other groups making decisions about biodiversity protection.

Windust said the group had been looking for a self-baiting, self-setting trap for years.

Traditional traps had to be baited by hand and once a trap was triggered it had to be reset manually.

However, baits only lasted about a week in Northland conditions before they went mouldy, and resetting traps was such a labour-intensive task most pest control groups only managed it once a month.

The AT220, on the other hand, rebaited itself every night and reset itself constantly as long as the battery charge lasted.

In Bay Bush Action’s experience, the battery could go about three months without a recharge.

The traps also turned themselves off during the day, saving battery life and reducing risk to non-target species.

The AT220 worked for both rats and possums, reducing the number of traps required.

Windust said the group was now starting to plan re-introductions of native birds and kauri snails which had long since disappeared from the forest.

If he could choose any bird to bring back it would be the kākā, a forest parrot that played a vital role in spreading seeds from kauri cones.

Bay Bush Action started in 2011 and now has 500ha of Ōpua Forest under multi-species post control. With help from the Jobs for Nature fund it hopes to eventually have pest management across the entire 2000ha forest.

■ Go to www.baybushaction.org.nz/ora for more information about the trap trial.