Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Trapping stoats and ship rats – a low-cost option for their control

Over the past decade more community-based groups have been carrying out pest control in New Zealand, but they are constrained in the amount of control they can do with available funding. Consequently, there is a demand for low-cost tools that community groups can use. Additionally, there is an increasing acceptance that all vertebrate pest control programmes must meet national welfare standards. For traps, there is now a guideline in place for testing their welfare performance. The Victor® Easy Set® rat trap is one trap that meets both these requirements for use against ship rats, but has potential to also be a low-cost trap for controlling stoats.

In 2011–12, Grant Morriss and colleagues made some minor modifications to the Victor® Easy Set® trap to make it more suitable for catching stoats, and tested the modified trap against stoats and ship rats in pen trials. To increase the likelihood of the trap killing stoats consistently, the treadle trigger was changed to a pull trigger and a plastic shroud was added to direct and align the animal at the front of the trap to ensure it was struck lethally and consistently across the top of its head. The modified trap was tested in vertical (Fig. 1) and horizontal sets (Fig. 2) against both stoats and ship rats. The vertically aligned trap was set 20 cm above the ground to minimise access by ground birds such as kiwi whereas the horizontally set trap (on the ground) was placed inside a purpose-built corrugated plastic tunnel that also limited the access of non-target species. During trials, the trap had to render each of 10 animals captured irreversibly unconscious within 3 minutes to meet the trap-testing welfare guidelines for kill traps. In the first trials, some stoats were struck on the neck and escaped, so the shroud length and trigger design were modified and the trap retested. The further-modified trap then passed the welfare standard for both species in both set types.

The modified Victor® Easy Set® trap provides a low-cost, low-weight, humane trapping option for community groups to control stoats and ship rats. The two setting options (vertical and horizontal) minimise the risk of capture of non-target species such as kiwi and weka. Though community groups could make their own modifications to the Victor® Easy Set® trap, two NZ suppliers of pest control products are currently investigating making modified traps commercially available.

This research was funded by the Ministry of Business, Innovation and Employment (Programme C09X1007 Strategic Technologies for Multi-Species Pest Control).

Grant Morriss, Sam Brown, Jane Arrow & Bruce Warburton