2022 Rat Pilot Results

The 2022 rat pilot was comprised of three separate operational trials. Each trial was designed to answer questions that island-wide rat eradication poses.

Ostend Trial

The Ostend trial ran from May to September 2022 and included a variety of complex urban habitats such as the Resource Recovery Park, storage facilities, cafés, industrial businesses, wetland and mangroves. While there is much known in New Zealand about eradicating rats in rural, bush and forested areas, there is little known about eradicating rats from urban environments.

Key Learnings from the Ostend Trial:

1. What tools will work in challenging terrains such as tidal mangrove habitats or wetlands?

●       Phil Salisbury designed an enclosed, floating bait station which proved effective for the duration of the trial.

 2. At what scale and density would eradication tools have to be implemented in residential and industrial areas including both inside and outside building structures to be successful?

●       The 25m x 25m grid of bait stations was successful in removing rats. Bait stations were not necessary inside most buildings. The Placemakers warehouse and inside the Resource Recovery Park Operations Building were the only places that had bait stations inside.

 3. Do different habitats require a different density of tools and/or approaches?

●       Yes. 50 m x 50 m grid was used in mangroves due to difficult access but didn't affect the efficacy of the programme.

 4. What detection systems work in urban/industrial/commercial/farmed areas at low densities?

●       There were a few rat detections around the Resource Recovery Park in week 14 and week 16, which were considered likely to be reinvasions. Detection signs included chew marks on a bait station, wax blocks, camera footage and finally snap traps, while chew cards failed to detect invaders.

 5. Is there an impact on pets from tools used in the eradication?

●       No impact on pets was reported

Kennedy Point Trial

The Kennedy Point trial ran from May to October using only traps to remove rats. There were 499 traps across 30ha of the peninsula. There were also 133 bait stations in the adjacent interception zone, to stop rats migrating in from outside the trial area. 

During the trial the traps were checked 12,300 times. There were also 143 monitoring devices checked 598 times in the last four weeks of the trial to determine if rats were still in the trial area .

Key Learnings from the Kennedy Point Trial:-

• Can rats be removed using only traps? 

• Rats could not be eliminated with only trapping but traps are a useful control tool . Although 681 rats were removed during the trial, there were still a small number of rats captured every week right up to the end of the trial. Rats were also still being picked up by the detection devices.

• Does the suppression zone prevent reinvasion?

• Given not all rats were removed from the Kennedy Point trial area, it was not possible to assess whether the interception zone prevented reinvasion. Bait consumption observed in the interception zone could have been from rats immigrating into the trial area or from survivors leaving the trial area.

• What are the most sensitive detection devices?

• Detection devices used were wax blocks, chew cards, tracking tunnels and trail cameras. The number of detections was too low to compare the efficacy of different devices, however, all four device types detected rats. Even though not statistically significant, detection rate was the highest for trail cameras and lowest for tracking tunnels. Therefore a combination of different devices was needed to increase rat detection probability.

• Are traps a tool that can be used in challenging terrain, i.e. cliffs?

• Traps are a tool that can be used in challenging terrain e.g. cliffs, given qualified ropes workers are available to check these traps. It is  very demanding on time and financial resources.

• Other Findings:

• Rats on Waiheke breed through winter – an important finding on our journey to make Waiheke predator free!

• Community support was strong and necessary for the success of the trial.

• A well-trained and motivated field team, including local contractors and volunteers, results in high-quality delivery and data.

Rocky Bay Trial

The Rocky Bay trial ran through the months of June and July 2022 in collaboration with the Rocky Bay Ratbusters. For this trial, cameras were set up on both Rocky Bay Ratbusters bait stations that are serviced quarterly and Te Korowai o Waiheke bait stations that were serviced weekly, to gain a deeper understanding of rat behaviour around bait stations.

Over 275,000 images were collected from the 86 trail cameras in Rocky Bay during the trial and captured learnings were shared with the community on September 11th.

Key Learnings from the Rocky Bay Trial:

Does rat activity around bait stations differ between areas with a community rat control group conducting quarterly bait pulses and areas without ongoing control?

●       Rat activity was higher in areas without community rat control in week one

●       Scheduled community rat control was able to dramatically reduce rat numbers within two weeks of deploying bait

Does rat activity differ between bait stations serviced weekly and quarterly?

●       Weekly servicing does not further improve control outcomes compared with a quarterly pulse

●       After six weeks of baiting, rat activity was very low at all weekly serviced bait stations

●       Low activity at the weekly serviced bait stations with fresh bait after week 6 indicated very low abundance of rats in the whole trial area.

Thanks to Rocky Bay Ratbusters for collaborating on this trial!