Rat Pilot Trials on Waiheke Island
STEVE COOK (Communications Manager, Te Korowai o Waiheke)
Markus Gronwald talks to community group about trapping operations on Waiheke (Photo: Te Korowai o Waiheke)
Te Korowai o Waiheke is a charitable trust established by the local community with the aim of making Waiheke the first predator-free urban island in the world. An island-wide stoat eradication has been running since February 2020 and there are strong indicators that the programme is already making a difference to the island’s ecosystem, with exploding kākā numbers and recent sightings of kākāriki.
Floating bait station used in mangroves (Photo: Te Korowai o Waiheke)
The second phase began in 2022 with rat pilot operational trials taking place at three different island locations. Waiheke is a diverse island - from the residential west to the rural east, and everything in between. It is therefore crucial that technical and social factors are tested across a wide range of different environments and habitats to develop a plan to eradicate rats from the whole island.
The first trial completed was in Rocky Bay, in collaboration with the local rat control group ‘Rocky Bay Ratbusters’. The objective was to gain a deeper understanding of rat behaviour around bait stations and the effectiveness of servicing the bait stations at different intervals. Over 275,000 images were collected from the 86 trail cameras during the trial. It was found that community rat control was able to dramatically reduce rat numbers within just two weeks of deploying bait and that weekly servicing does not further improve control outcomes compared with a quarterly pulse.
Kennedy Point Team Leader Owain Tanner (left) demonstrates trap setting to Chris Anderson and Horst Meyer ahead of the operational trials (Photo: Te Korowai o Waiheke)
The next trial was in Ostend - a complex urban area including a Resource Recovery Park, storage facilities, cafés, a primary school, industrial businesses, wetlands, and mangroves. The main objectives were to determine at what scale and density eradication tools would have to be deployed and to develop tools that could be used in wetlands and mangroves. The trial was successful in completely removing rats from the area, using a 25 m x 25 m grid of bait stations. It also resulted in a new innovative floating bait station to use in mangroves, thanks to team leader Phil Salisbury. This proved effective for the duration of the trial.
The last trial was in the residential area of the Kennedy Point peninsula. It covered 30 ha and contained a network of 500 traps. The main objective was to test whether rats could be completely removed using traps alone. Over the trial period, there were 12,300 trap services and 650 rats were caught. However, tracking tools and traps showed that some rats remained and there was evidence of breeding all year round, demonstrating that although traps can control rat populations, they are not an eradication tool.
All rat trials as well as the stoat eradication project demonstrated a clear need for community engagement and support. This ranged from the willingness to host traps and bait stations on private property to the practical help of volunteers. The community has also been the eyes and ears of the project with the majority of recent stoat catches resulting from people reporting sightings.