An ambitious eradication project in the Palmerston Atoll, Cook Islands.
By Souad Boudjelas and Em Oyston, DOC.
We were so excited when we first heard about the community on Palmerston wanting to remove the rats from their atoll. Why? First, a community taking the initiative, and second, the opportunity to help improve the wellbeing of the people and the native wildlife by eradicating rats on an inhabited island.
To date, most rat eradications have been on uninhabited islands, while only a handful of inhabited islands have been cleared of rats. So, a lot still to learn!
Inhabited islands are complex environments. For example, the presence of livestock, and crops present the rats with other food sources to the bait and may put them off from eating the bait, increasing the risk of eradication failure.
Prior to 2023, two islands of the Palmerston Atoll had rats: Palmerston Island, also referred to locally as Home Island, had ship rats and kiore, and Cooks Island had kiore.
When we asked the community why they wanted the rats off their islands, they told us that rats damaged their crops, ate and spoiled their food, caused a nuisance around their houses, posed health risks, and preyed on island fauna, including ground nesting seabirds. Their goal was to improve their food and water security, protect their health and wellbeing, and safeguard their native fauna and flora.
Left: Map of Palmerston Atoll | Google Earth. Right (top): A red tailed tropic bird, one of the native species preyed upon by rats | Alanna Smith, Te Ipukarea Society. Right (bottom): Home Island, Palmerston Atoll | Alanna Smith, Te Ipukarea Society.
The New Zealand Department of Conservation, in partnership with the Palmerston Island Administration and community, the Cook Islands National Environment Service and Ministry of Agriculture, and the local NGO, Te Ipukarea Society, completed a rat baiting operation on Palmerston Island (the only inhabited island) and Cooks Island of Palmerston Atoll in August-September 2023.
The operation was the culmination of months of hard work assessing the feasibility of eradicating the rats, which involved discussions with the community around requirements and acceptability of methodology, planning and logistics, managing risks, and preparing the island for the operation.
Getting the team, the rat bait and equipment to Palmerston was quite a challenge because of remoteness and irregular transport. The uncertainty around securing transport to and from the island kept the team on their toes for a while. Perseverance paid off at the end.
The community led the on-island preparations for the baiting operation
To enhance the chance of success, there were several important issues to be addressed by the community before the operation could commence. Solutions to these issues were discussed and agreed in consultation with the community.
One major issue was the presence of pigs and chickens (both wild and domesticated) on Home Island. They presented significant risks to the success of the operation due to their potential for removing bait destined for the rats, and presenting an alternative food source which may deter the rats consuming the bait.
Of the 17 pigs on the island, 14 were culled (and used for consumption) and 3 were moved to Primrose Island where they were penned and provided with food and water. After the operation and after baits had fully degraded, 15 replacement pigs (funded by the project) were returned to Home Island. The pigs on Primrose will be returned later.
Left (top and bottom): Penned pigs and chickens on Primrose | Alanna Smith, Te Ipukarea Society. Right: All hands on deck catching the chickens | Alanna Smith, Te Ipukarea Society.
All domesticated and wild chickens were culled, other than two small, domesticated flocks that their owners chose to move into husbandry on another island. Once the operation was complete and baits had fully degraded, these flocks were returned to Home Island and used as breeding stock to replace the culled domestic chickens.
Biosecurity to stop invasive species
The community appreciates the risk of rat re-invasion from incoming ships and cargo, as well as the threat of invasion from other invasive species. The community also understands the need for them to remain vigilant for invasive species and have in place adequate biosecurity measures. This is reflected in the Island Council funding a biosecurity officer role on Palmerston and applying agreed biosecurity measures.
As part of the eradication project, training and equipment have been provided to support the biosecurity officer.
Biosecurity infrastructure consisting of DOC200 trap boxes have been permanently positioned around Home Island and are checked immediately prior to and after cargo or passengers arriving on the island. This is in addition to temporary chew cards and tracking tunnels placed to detect any unwanted arrivals.
An island incursion response kit comprising of wooden tunnels for housing monitoring and removal tools, mouse and rat traps, bait stations, wax tags, and rodenticide bait, was provided to safeguard the achievement and investment of eradicating rats from the atoll.
The Palmerston Island Administration and Island Council are also working with the vessel operators to ensure all vessels transporting people and goods to their island remain pest-free.
Latest update from the island
All of us involved are feeling positive about the success of the eradication; no rats have been detected during the validation monitoring. From what we know about the rat ecology in tropical environments and the time elapsed since the operation was completed, they would have bred by now and would be detectable, especially around the settlement.
The positive outlook is backed by anecdotal reports from the community seeing a substantial increase in tavake (red-tailed tropic birds) on Cooks Island, as well as a significant increase in seedlings of mahogany and puka.
On Home Island, the community have enjoyed a whole crop of sweet nuts (young green coconuts from a variety of coconut tree) or nu mangaro (as locally known) after years of hard competition with the rats. Sweet nuts are a culturally significant food source for the community on Palmerston. Mangoes and sugar cane are also doing very well.
They also report seeing an increase in moko (lizard) abundance on the island.
The people on the island are just happy to no longer have to share their homes and their environment with the rats.
We anticipate declaring the result of the eradication in September. Watch this space!
The following video was made by Alanna Smith, Te Ipukarea Society, during the rat baiting operation. Check it out to hear more about the project.
This work is funded by the New Zealand Ministry of Foreign Affairs and Trade (MFAT) under the Managing Invasive Species for Climate Change Adaptation in the Pacific (MISCCAP) project, and is delivered through the Pacific Regional Invasive Species Management Support Service (PRISMSS).
The New Zealand Department of Conservation, the Secretariat of the Pacific Regional Environment Programme (SPREP), and Manaaki Whenua-Landcare Research have joined forces to support Pacific Island Countries and Territories to take stronger action against invasive species, and thereby build resilience to climate change.
