2023 Oneroa Rat Trial Results

The Oneroa rat trial ran from 1st May to 13th October 2023. 1670 bait stations were deployed in a 25m x 25 m grid. After 10 weeks no bait was being taken from bait stations, so monitoring devices were deployed, including trail cameras, chew cards, and wax blocks. Subsequently, there were a few rat detections made each week and so the original trial was extended by 6 weeks (the trial was originally scheduled to finish on September 1st). 

During the trial extension, additional techniques were used to catch the last elusive rats; these included scent lures and an alternative bait. In week 25 (the final week of the trial extension) there were zero rat detections.

During the Oneroa trial, the team carried out a huge 40,000 bait station services (cleaned and rebaited) and checked monitoring devices 25,000 times.

Oneroa was chosen for the rat trial because of its unique make-up of highly concentrated residential, hospitality, and holiday home properties. Learning what is needed to remove rats from such areas will be critical to the success of an island-wide rat eradication. There is much known in New Zealand about eradicating rats in rural, bush, and forested areas, but there is relatively little known about eradicating rats from urban environments.

Key Learnings from the Oneroa Trial:

The three key questions for the trial were effectively answered:

1.  Can bait stations be used to remove all rats from complex areas which include hospitality and holiday homes?

Yes, but different bait and lures could be needed to encourage the last rats to go into the bait stations.

2.  Will all sectors of the community support the project?

Yes, community support was fantastic with over 96% of residents in the trial area agreeing to host a bait station, and a lot of positive feedback throughout.

3. Will we be able to acquire all necessary permits and consents?

Yes, these were all obtained. Holiday homeowners were sometimes difficult to get hold of to obtain permissions, but persistence was key.

There were also a number of additional valuable insights:

• Environmental factors must be considered, including housing density, waterways & vegetation.

• Wet weather impacts the attractiveness of bait and could be a factor in an increased overall rat abundance.

• Rats are complex creatures and catching the last 10% takes 90% of the work.

• Scent lures seemed the most effective method of attracting the last wary rats into bait stations.

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:

1. 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.

2. 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.

3. 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.

4. 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.

5. 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:

1. 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

2. 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!

2022 Trial Results