Windy Hill Sanctuary on Great Barrier Island has now completed its 2.5 year Goodnature A24 rat trap trial. A report just released explains the challenges encountered during the trial, the results, and a cost-benefit analysis of the Goodnature Traps Vs the regular trapping and toxin regime of the Sanctuary.
Windy Hill Sanctuary Manager, Judy Gilbert, provides this report summary:
The A24 Goodnature Rat Trap Trial was undertaken between February 2016 and August 2018 in a 100 hectare area within the Windy Hill Sanctuary on Aotea Great Barrier Island. The project was a collaboration between the Great Barrier Local Board, Auckland Council, Department of Conservation (DOC), Goodnature Ltd, and the Windy Hill Sanctuary.
The purpose of the trial was to establish how effectively the non-toxic, self-setting, multi-kill Goodnature A24 trap was at reducing both ship rat and kiore densities within a pest managed Sanctuary. This objective supported the local community aspirations to find ways to manage these pests with non-toxic methods.
Two hundred and ninety-three A24 Goodnature traps were established over the 100 ha trial area by a team made up of personnel from Auckland Council, DOC, Goodnature, and the Windy Hill Sanctuary. The regular Windy Hill Sanctuary regime of SnapE rat traps in wooden trap boxes alternated with 100-150 grams of diphacinone paste was continued in an adjacent area to compare results, and a control area of no traps or toxins was also monitored.
The Good Nature Trial area involved:
- Monthly trap checks for the first six months to test functionality and enable identification of rat species. From then, every 3-6 months following the replacement of the manual lure with the chocolate flavoured auto-lure pump (ALP).
- Gas canisters and lures replacement at 6 monthly intervals.
- Rat monitoring with tracking tunnels carried out in accordance with DOC standards undertaken 5 times a year to assess efficacy of A24s at reducing rat densities and the results compared with neighbouring pest managed areas using a mix of traps and diphacinone.
- Eleven motion triggered cameras were established for the first three months to record activity.
Tracking tunnel results showed that the Goodnature traps failed to bring rat tracking tunnels below 20% over two and a half years except for the July 2018 run when these reached 12.5 %.
However, the Windy Hill Sanctuary standard management regime of traps and diphacinone bait in adjacent pest managed areas for that month were 7.5% and 0% – a pattern that was consistent throughout the project timeframe.
The tracking tunnel averages over the whole study period were 8.5% for the Windy Hill Sanctuary trapping area and 27.7% in the Good Nature Trial area.These monitoring results clearly indicated that the Windy Hill Sanctuary traps and toxin were much more effective in keeping rat numbers at low levels.
The Good Nature A24 traps were initially spaced 50 metres apart. This was reduced to 25 metres apart in August 2017. While this improved the tracking tunnel rates from an average of 32% to 25% in the Good Nature trap trial area, they were still well above adjacent areas managed with traps and diphacinone.
In general, the Good Nature traps were found to be reliable, with good functionality. The main issues identified were the glugging up of bait around the trigger which resulted in some devices off-gassing and a lack of consistent bait release from the automatic Lure Pumps (ALPs).
To get a comparative picture of the efficacy of the ALPs in other areas contact was made with Mt Bruce, Boundary Stream, Ark in the Park, DOC Te Anau (Lyndsay Wilson), and the Hollyford Community Trust. A spot check protocol was shared. A general consensus shared by these A24 projects is that four months is the most effective life for the lure in the ALPs, rather than the expected six months.
A subsequent cost-benefit analysis of the Good Nature trapping area against the standard regular manual checking of SnapE traps and diphacinone pulses showed the overall cost of running the A24 grid was approximately 1.8 to 1.9 times higher than that of an equivalent grid of snap-trap stations and bait, despite the reduced amount of labour required.
In summary, not only was the standard Sanctuary methodology more cost effective, it was also more successful at keeping rat abundance at lower levels.
The failure of the Goodnature A24 trap to reduce rat densities sufficiently resulted in the devices being removed from Windy Hill Sanctuary in August 2018 and returned to Auckland Council.