Baiting Method

When was the baiting approach decided?

The overall baiting approach was decided early in the planning process and was approved in permits from the necessary regulators. This included aerial broadcasting over uninhabited parts of the island and a combination of hand broadcasting and bait stations in the settlement area.  The actual treatment methodology over individual properties was discussed and negotiated with individual leaseholders and residents through Property Management Plans in accordance with the regulatory approvals and conditions received.

Why aerial baiting? Why not do the whole island with bait stations?

It was simply not possible to safely and effectively distribute the bait on areas such as the Southern Mountains and Northern Hills by any other means. Aerial application of bait has been the primary method of dispersal in previous successful eradications because it gives every rodent on the island an opportunity to find and eat enough bait within a short period of time. Due to the small size of some mouse territories, it would have required putting bait stations at close intervals over the whole island, including the cliff sides of Mt Gower and Mt Lidgbird, which was simply not feasible.

Could the SenesTech fertility control method have been used?

Fertility control has been used with limited success as a method of pest management in a few species, primarily larger mammals, where individuals can be targeted for treatment. Experimental sterilization methods have included chemicals and proteins delivered by vaccine, and genetically-modified viral pathogens. However, the effectiveness of these experimental techniques in the wild and their impacts to non-target animals are unknown.

The possibility of using a new rodent sterilisation technology called “Contrapest”, developed by SenesTech Ltd, was considered with the following issues identified:

  • The product “Contrapest” aims to reduce rat populations through sterilisation, limiting fecundity but leaving some animals to defend territories i.e. ongoing control not eradication.
  • It requires every female to be dosed with the product i.e. it needs to be regularly dispensed as there is no inherited or contagious transmission of the reduced fertility.
  • The fertility control compounds (VCD and Triptolide) are not species-specific and could affect other mammals including humans.
  • Currently the product is designed for rats although the developers state that it has the potential to be modified to target mice, along with other species, although dispensing the appropriate dosage is problematic at this stage.

The product was not suitable for the rodent eradication program on LHI as:

  • The product aims to reduce rat numbers, not eradicate them.
  • The product needs to be ingested over a prolonged period (approx. 75 days) and all female rats would need to be exposed to the product. This would effectively mean that the product would need to be put out continually for the foreseeable future.
  • While reducing rat numbers would have some benefits, only total eradication of rats and mice could give the anticipated ecological, social, economic and human health benefits.
  • The product is currently dispensed by adding it to water. This is problematic for LHI as dispensers would have needed to be put over the whole island at approximately the same spacing as bait stations. The product needs to be consumed over many feeds as it affects the reproductive system slowly meaning that the bait would need to be made available in every territory for a prolonged period to affect even one generation of rats.
  • Even if the product was used on the accessible areas and was able to reduce numbers, this would only be short term while the product was being dispensed. Also, rodents from the untreated areas would soon move in as resources, food and territory were freed up
  • The current product Contrapest is only for rats which would leave mice untreated.

Contrapest has been investigated for both the LHI program and by other rodent eradication organisations internationally. Its use would be experimental, hence it has not been considered a feasible option for rodent eradication currently or in the foreseeable future.

Repeated baiting of uncertain oral contraceptives on an inhabited and rugged island across seasons or capturing, vaccinating, and releasing every member of a single gender of the LHI rodent population was not considered feasible. The lack of data and tools disqualified the use of fertility control from detailed consideration.


How much poison was used?

Less than 1.2kg of the active ingredient (toxin) Brodifacoum has been used in total over all baiting applications.

Each pellet has a Brodificoum concentration of 20 parts per million, 2 ½ times lower than the bait that can be bought in shops.

Can the Board do more than two aerial bait applications?

No, we only have approval for two.
The project, including aerial baiting, cannot deviate from what was presented in our original application documents as this is what our permits and approvals are based on. More than two aerial baiting applications would be in breach of our approval conditions and exceed our project budget.

Did the community and visitors have advanced notice of a bait application?

Before any bait was distributed on the island, the community and all tourists were informed via emails, letters, posters, phone calls and handouts about the nature and timing of the operation and the need to avoid ingesting or handling baits.

Was the aerial baiting done over people’s houses?

No. Aerial baiting was not undertaken in the settlement area. Residents on the edges of the settlement had a say in how far they wanted aerial baiting from their properties. We could not legally aerially bait within 150m of a house without owners consent. Where we had people’s consent we still did not aerially bait within 30m of houses. There were three different setups for the bait buckets (see below). The directional swathe was used for the edges of the aerial baiting areas to only spread bait on one side of the helicopter, i.e. away from houses.

If the program has been considered safe, why do you need to do monitoring afterwards?

Scientific monitoring is considered standard practice and prudent for a project such as this. Monitoring before, during and after provides evidence of whether anything has changed or not. It can indicate progress toward achieving project goals, it can provide reassurance, it can be used in decision making for many other projects.

How was the baiting undertaken and over what time period?

Baiting was undertaken using a combination of aerial, hand broadcasting and bait stations. No aerial baiting was undertaken over the settlement area. The aerial and hand broadcasting was undertaken twice over a one-month period to minimise any gaps in the bait broadcast and expose any surviving young that have recently emerged from the nest after the first baiting. Bait stations around the settlement area were monitored by work crews and loaded with bait as required between late May and November.

After a non-toxic baiting trial on Lord Howe Island in 2007, results showed that both 5.5 mm and 10mm baits in all three habitats were in advanced stages of decomposition after 55 days and 164.2 mm of rainfall.  Further monitoring showed that all baits had completely disappeared by 100 days.

Bait stations will be physically removed from properties following ground baiting operations, with the final ground baiting date being Friday November 1st.

How did you plan to get the rodents off the sides of the mountains especially where there are cliffs and caves?

Spreading bait from a bucket slung under a helicopter has been very successful in removing all rodents in similar situations such as Campbell Island (11,300 hectares) which has 300m cliffs and sea caves. A successful rat and cat eradication was undertaken on Raoul Island (2900 hectares, ) in the Kermadec group – about 2000 km east of Lord Howe – between 2002 and 2006. Raoul is similar topographically to Lord Howe although its mountains at 516m are not a high as those on LHI. A project is also underway on 352,800 hectare South Georgia Island in the South Atlantic which includes mountains up to 2900m in height.

What happened to all the dead rodents after the baiting occurred?

Approximately 50-70 employees, many from the island community, were required for the eradication operational phase to assist with its implementation. With the bait station monitoring occurring throughout the settlement area, crews were also engaged in collecting as many dead rodents as possible and disposing of them appropriately to minimise the impacts to residents and the environment.

In the vast majority of cases, rodents were found to return to underground nests where they died.

Why was 2019 the right time to eradicate rats and mice?

Lord Howe Island is not unique in having rats and mice, but it did have a rare opportunity to solve the problem. Most inhabited islands around the world have rats, as does every major city, and some manage them better than others. Lord Howe did a good job of managing them around the settlement but they were still impacting on most of the island and they wouldn’t have gone away unless we did something to get rid of them.

A window of opportunity

The complete eradication of invasive rodents has been carried out on over 300 islands around the world. It had been done elsewhere and success was now possible on Lord Howe Island. There were solid precedents for what needed to be done and how to do it. Careful feasibility planning indicated it could be done here, and this led to the availability of funds and expertise to protect Lord Howe Island. The window would not have stayed open for long; if the eradication did not go ahead, the funds would have gone back to the mainland as they were not available for other projects on the island.


Everywhere in the world we are seeing a frightening trend: resistance to once effective treatments including antibiotics and pesticides. This is currently happening with TB where strains are appearing which are resistant to all normal antibiotics. Similarly, many other bacteria are becoming resistant to penicillins (which were far more effective when introduced 70 years ago). Prior to the REP, mice on Lord Howe Island were already resistant to Warfarin, one of the earlier rodenticides

Imagine an island without rats and mice

Lord Howe is special in many ways, and its unique wildlife, history and its people are reflected in its World Heritage status. Removing rodents completely and for good makes it even more special and enhances a worldwide reputation as an ecotourist destination. Rodents were only being controlled on a small percentage of the island. Elsewhere they were having a major impact on the wildlife and vegetation. Without the rodents, plants and wildlife will flourish. People no longer have to bait around their homes and businesses. There now will be no more risk of the ongoing poisoning of native species that was happening or the risk to children or dogs.


How do we keep rodents off the island after the eradication?

The LHI Biosecurity Strategy has recently been revised to significantly increase the level of protection from introduction (or reintroduction) of invasive species. It is important to note that biosecurity on the island will be improved against a number of non-native species in order to keep a wide range of invasive plants and animals off the island.  However, special consideration will be given to keeping rodents off the island. The Biosecurity Strategy will continue to be revised and updated after the REP process.


Wildlife Impact
What will be the impact on birds and plants?

Expect increasing numbers and types of birds and other wildlife

Eradicating rats and mice from LHI is expected to result in marked increases in the abundance of land birds and seabirds. Eradicating these rodents from LHI will reduce the risk of extinction of many threatened species and help protect the island’s biodiversity and World Heritage status.

There will be substantial increases in the distribution and abundance of the LHI skink and gecko, all species of land snails, as well as many other creatures. There will be an increase in the abundance of seeds and seedlings, increasing recruitment of many threatened plants and enhancing the process of forest regeneration.

With the rats and mice gone, bird populations will flourish, increasing in abundance to levels not seen for many decades. Nesting colonies of storm-petrel and Kermadec petrel are likely to re-establish on the main island. Also, the opportunity would then exist to return some of the species that have been lost from LHI, such as the, fantail, warbler, pigeon and boobook.

Biodiversity monitoring has been conducted throughout the project. Once complete, it will provide quantitative results on changes in species richness and abundance.

What would happen if bait went into the sea?

To minimise the amount of bait that went into the sea, as much as possible of the area around the lagoon and other sites such as Ned’s beach was hand-baited. While it was not possible to guarantee that no bait would go into the sea where aerial broadcasting took place, as it was important to get bait as close to the high tide line as possible, this was minimised by the use of a deflector in the bucket which directed the bait just out one side.

Studies on other island eradications have shown that the small amounts of bait that enter the water disintegrate quickly, particularly in areas with high wave action.  The low-moderate application rate of brodifacoum (0.4 g/ ha) for the LHI REP, low solubility, high dilution factor in the marine environment and one off eradication mean that any sea water contamination would be of a sufficiently low magnitude as to not present a significant risk to marine life or humans through any activity (including swimming or snorkelling).

What about fish, was it true there would be a ban on catching and eating fish after the eradication?

No, there was no fishing ban proposed. No impacts to fish and marine life were expected due to the very small amount of bait likely to enter the ocean, the huge dilution factor and because Brodifacoum is practically insoluble in water. The Human Health Risk Assessment overseen by the NSW Chief Scientist looked at the potential for human exposure from fish and concluded that transfer of Brodifacoum to seafood would not be expected to present a risk to residents and visitors. It did not recommend the need for a fish ban here, however to be extra safe we advised visitors and locals to avoid eating the livers of fish caught in the lagoon for the duration of the project.

As an additional precaution, samples of sea water and local fish were laboratory tested for any Brodifacoum residue before and after baiting occurred.

What about the whale strandings on Kaua‘i?

There have also been unsubstantiated claims that the stranding and death of five pilot whales in Kauai could be linked to the Lehua eradication. Personnel from multiple agencies worked together to conduct a necropsy (post-mortem examination) on all five whales to investigate the cause of stranding. The preliminary results showed no obvious cause of death. Samples were taken and sent out to labs for further analysis which may provide more insight into the general health of these animals as it may relate to possible infectious pathogens, toxins, trauma, and individual organ function. The liver tissue of the whales was also be tested for the presence of the rodenticide (diphacinone) which was applied at Lehua Island. Samples came back negative for any traces of rodenticide, ruling out poisoning from the eradication as a cause. Mass stranding’s for this particular species are fairly common globally. Since pilot whales are social, when one individual strands, others tend to follow (not necessarily for the same cause of stranding).

World Heritage
How does the eradication affect Lord Howe Island’s World Heritage Status?

Successful eradication would protect and enhance the Island’s World Heritage Status. Tim Badman, the Director of the IUCN World Heritage Programme wrote to confirm support for the program.

Why are islands so important for biodiversity?
  • Islands make up less than 5% of the earth’s land area, but are home to an estimated 20% of all bird, reptile, and plant species.
  • Islands also contain 40% of all critically endangered species, and extinction rates are disproportionately greater on islands.
  • 80% of all known extinctions have occurred on islands.
  • Nearly a quarter of the world’s plant species exist only on islands.
  • Some individual islands are home to hundreds—or even thousands—of plant and animal species found nowhere else in the world (endemic species). Other islands have a few or even a single unique endemic species.
  • Many islands are home to species yet to be described by science. We don’t even know what we might be losing—such as sources of food or medicine.
  • On islands, species under threat of extinction have nowhere else to go so they must be protected on-site.
  • Many migratory species breed and raise their young only on a few islands, or sometimes only on one single island.

Source: Island Conservation


Was human health at risk during the REP?

No. Provided basic precautions were taken, the risk of brodifacoum poisoning during the eradication was remote.

The previous practice of using rodenticides (such as Ratsak Plus® and Talon®) containing brodifacoum on an ongoing basis for rodent control on Lord Howe Island posed an ever present risk for residents, their pets and local wildlife. The eradication of rodents removes the need for the ongoing use of rodenticides and the risks that go with it.

How should people interact with baits?

For the most part, the risk to human health associated with the eradication operation was similar to those that previously existed through the domestic use of products like Talon®. In brief, it was suggested that the baits be treated like any other poison, i.e. not eaten or handled. Residents with children already exercised care when using baits domestically. Baits previously used domestically have a much higher concentration of brodifacoum, 2.5 times greater than the baits that were used in the eradication. However, there were more baits on the ground during the eradication and it was recommended care be taken with children and those unable to read the signage that is posted.
The only way residents could have been exposed to brodifacoum absorption from the skin was by handling baits directly. However, for there to be any adverse effects a person would have needed to handle large quantities of bait for long periods of time. The risk of such exposure was negligible.

What should someone do if they came into contact with bait?

Swallowing one or two baits seldom requires medical treatment. In the extremely unlikely event that medical treatment was required (involving vitamin K injections), antidotes were made available. Nevertheless, anyone who suspected brodifacoum poisoning was recommended to seek medical advice.

Visitors and Residents REP Information Sheet PDF 499 KB

Was there a danger from dust?

Only those working directly with the baits around the helicopter were exposed to significant dust. All of these staff members wore protective equipment.  Bait was not spread in high winds which minimised the risk of any dust being dispersed.

What about water tanks?

Aerial baiting was not conducted over the settlement and was not conducted in high winds. Combined with the fact that brodifacoum has very low solubility in water i.e. would sink to the bottom of a tank and bind with any material there, it means that there was effectively no risk to human health from dust in water tanks.

What about my vegetable garden?

Brodifacoum has very low solubility in water, and therefore is not taken up by plants. Therefore, no exposure risk was anticipated from plant-based food grown on the island.

As an added precaution there was no bait put in vegetable gardens. These areas were baited by bait stations or hand broadcast bordering gardens as per the Property Management Plan for each site.

What about the water and soil?

To date, brodifacoum residues have not been detected in water bodies following any aerial baiting operations—not surprising, given that brodifacoum has very low solubility in water.

The baiting operation was conducted to avoid bait going into the lagoon and minimised the entry of baits into the ocean.

What we already knew, fresh water:

From other aerial baiting operations, we knew that there was a very low chance of any streams and other water bodies on Lord Howe Island containing detectable levels of brodifacoum, much less biologically harmful concentrations, as a result of the eradication.

Because brodifacoum has very low solubility in water and binds strongly to soils it was unlikely to get washed into the marine environment. Any baits entering streams or other water bodies sink, and disintegrate, usually within a few hours, depending on turbulence and rate of flow. The minute amount of brodifacoum in the bait (20 parts per million) settles in the sediment where it binds to organic material and breaks down.

Brodifacoum binds strongly to soil particles, where it is broken down by soil micro-organisms to its base components, carbon dioxide and water. While the cereal bait pellets disintegrate and disappear within 100 days or so, the toxin itself takes longer to break down but by this stage the concentration is so low that it poses no risk to humans or wildlife.  Laboratory studies have shown that brodifacoum is effectively immobile (i.e. not leached) in the soil.

Nonetheless, water samples have been collected at various intervals after the baiting and analysed by an independent laboratory to reassure residents and tourists that the water (along with locally produced milk and locally caught fish) was not contaminated.

In the marine environment, outside the lagoon:

Outside the lagoon, any baits that may have entered the ocean would be exposed to wave action and strong currents resulting in rapid breakdown and dispersal. This, together with the high dilution factor, and the fact that brodifacoum has very low solubility in salt water, means that the potential risk to marine organisms was very low.

In the marine environment, within the lagoon:

Within the lagoon, the physical breakdown of baits would not be as rapid, so entry of baits into the lagoon was prevented by hand distribution of bait, rather than aerial distribution, along the accessible shoreline of the lagoon. As there was very low risk of brodifacoum being at detectable levels in the streams, any water entering the ocean or lagoon was unlikely to carry detectable levels of brodifacoum.

Fact Sheet Brodifacoum – is it the best choice? PDF 774 KB

My Property

What happened on individuals' properties?

The Property Management Plans (PMPs) included the agreed baiting methods for each lease on the Island, including the settlement area. They were discussed and negotiated with the leaseholders / residents individually and considered mitigation of specific risks and areas of concern on individual properties. The PMPs do not impact on the tenure of the leases. As discussed during the Property Management Planning process, livestock owners only began reducing their cattle numbers once the operational phase proceeded.

What changes did individuals have to make?

Any available alternative food options for rodents (particularly food waste) posed a significant risk to the REP as it reduced the likelihood of every rodent eating a lethal dose of toxic bait.

To reduce this risk we asked that all food scraps be kept in a secure food waste bin and taken to the Waste Management Facility. This also included ceasing the dispersal of scraps as food for chickens and other livestock. While many residents were already in this routine, we did not wish to inconvenience anyone and provided a collection service to residents if requested. Our team Waste Management Officer, Josh Owens, began collecting food waste bins every Wednesday from the 3rd April.