Macquarie Island World Heritage Area
Plan for the Eradication of Rabbits and Rodents on Macquarie Island
The Plan for the Eradication of Rabbits and Rodents on Subantarctic Macquarie Island 2007
can be downloaded from our publications section.
Frequently Asked Questions
What is the problem with introduced mammals?
In recent years rabbit damage on Macquarie Island has increased significantly. This has resulted in serious vegetation degradation and is impacting on burrowing seabirds that require vegetation cover around their breeding habitat.
More recently, landslides at least partially caused by rabbit grazing were responsible for the deaths of penguins and damage to visitor boardwalks on the island.
Rodents are also having a significant impact on the island, with rats in particular eating the eggs and chicks of burrow-nesting petrels. With no vegetation on the island higher than tussocks, all species must breed on or in the ground, where they are easily found by rodents.
What is being done about the problem?
An eradication plan has been developed and work has started on some preliminary aspects of that plan, including:
- A trip to the island in April 2007 established an automatic weather station to assist in planning helicopter flights for spreading poison baits.
- Trials involving the deployment of bait pods and over-flight of penguin rookeries.
- North Head, which is a small peninsula located immediately north of the island’s main base, will be fenced off with a rabbit-proof fence, and rabbit control measures undertaken.
- 10 plots will be enclosed to protect specific plant species that may not recover from severe grazing.
- Two shooters will be deployed in spring 2007 to work on reducing rabbit numbers at specific locations.
Why has it taken so long to address the problem or rabbits and rodents?
Funding had to be identified for the plan. Beginning implementation without certainty of the funding available would be counterproductive in terms of planning and logistics.
Why was the rabbit and rodent 'explosion' not foreseen when the cats were eradicated from the island?
The dramatic increase in rabbit numbers since 2001 is the result of a combination of factors and associated cumulative impacts. The removal of cats has been one factor, but it is certainly not the only factor. Rabbit numbers were estimated to be higher in the 1960s when cats were present. This was the reason for introducing myxomatosis in 1979, which was the major factor in controlling rabbit numbers. The island’s rabbit population has developed resistance to the myxoma virus over recent years and additionally, it is no longer available in Australia, with the result that it is losing its effectiveness as a control mechanism. An additional factor is that there have been a series of warmer and drier winters that have contributed to higher survival rates of rabbit kittens.
How will the rabbits, rats and mice be eradicated?
The eradication of rabbits, rats and mice on Macquarie Island will be achieved by two phases of an eradication plan:
Firstly, helicopters will spread pellet baits containing brodifacoum – an anti-coagulant poison - that all three target species will consume. Trials using these baits were conducted on the island in 2005. Differential GPS computers in the helicopters will ensure accurate coverage of bait spreading which should eradicate all of the rodents and at least 95 per cent of rabbits. This technique has proven very successful in other island eradication operations around the world.
Following the bait drops, field teams will follow up on the ground eliminating surviving rabbits by shooting, fumigating and trapping them. Dogs will also be used to search for rabbits, and are considered critical in locating surviving rabbits in the rugged terrain of Macquarie Island.
Won’t poisoning the rabbits be cruel?
The use of poisons is an accepted practice in dealing with pest species. There is no other technique available which has proven successful in eradicating pest species on sub-Antarctic islands. Various toxins were considered and brodifacoum was identified as being the most suitable. All three target species (rabbits, rats and mice) are known to consume the baits. The toxin used is no different to rat poison available for household use.
Suggestions have been made through the media about releasing neutered cats, foxes, Tasmanian devils or other predators – what is wrong with doing that if they will eat the rabbits?
While cats were a predator of rabbits, they also preyed heavily on burrowing seabirds. In the 1970s an estimated 60,000 seabirds were eaten by cats each year. Any predator released on the island will eat whatever it can find, not just rabbits. For example, in New Zealand, stoats were introduced to control rabbits. This introduction is commonly regarded as one of the worst mistakes ever made in New Zealand due to their impacts on native animals and in particular, bird species.
Furthermore, the presence of a predator is not an eradication method – it is a control method and thus unsuitable for the goal of eradicating rabbits and rodents.
What about using myxomatosis and/or RHVD?
Myxomatosis has been used to control rabbits on the island for over 25 years and was the main control method. Further supplies are now unavailable and the virus is losing its effectiveness on the island. RHVD (calicivirus) is not an eradication tool but may be suitable in some areas for rabbit control. It is however ineffective against rodents so baiting would need to be done to eradicate them anyway. Additionally, the Calicivirus has not been as successful in moist cool environments such as Macquarie Island as in more arid areas.
What about just shooting the rabbits?
Shooting is occasionally used as a rabbit control method. It has never been used successfully to eradicate rabbits from islands. The rugged terrain of Macquarie Island and its size mean that shooting will not be a feasible option for eradication. Furthermore, shooting of rabbits will not achieve any reduction of rats or mice, which are also having serious effects on fauna and flora. It is important to note that this project is about eradicating these three species, and the techniques used in eradication operations are different to control operations.
What if a penguin or albatross dies from poisoning?
The baiting will be done in winter to coincide with the absence of most of the indigenous species on the island, thus minimising or avoiding any effects on their populations. Trials have been conducted on the island with non-toxic baits to determine the response of native birds to the baits, and operational planning reflects the need to keep non-target impacts to a minimum. Recovery of the vegetation on the island following rabbit eradication, and removing rats as a predator, will vastly improve conditions for all native species. Some species are vulnerable to secondary poisoning. The impacts of the baiting operation on wildlife and human health will be addressed in the Environmental Impact Statement that is being prepared.
When will the eradication program be undertaken?
Aerial baiting operations will be undertaken between May and September for the following reasons.
• There is less natural food around for the rabbits and rodents thus a greater attraction for them to eat the baits.
• There are lower number of rabbits and rats during winter (less breeding and higher mortality) so there are fewer animals to target.
• Baiting during this period avoids the breeding season for native animals thus reducing the chance of affecting them. In addition many native species leave the island for the winter avoiding disturbance to them.
• It avoids the summer tourist season so no tourism operators will be affected.
Why is the eradication program so expensive?
The high cost of the eradication program is mainly due to a number of factors – the isolation of Macquarie Island means the cost of shipping is significant. Helicopter operations are also expensive. A prolonged follow-up period searching out surviving rabbits requires sufficient staff to apply pressure to the rabbit population, so employment costs are a significant component. We would hope that some savings can be made, however comparable eradication programs have shown that it’s unwise to underestimate the cost of eradication of feral pests.
How long will it take?
The operation will take up to seven years.
Why so long?
A minimum of two years is required to achieve the relevant environmental and other approvals and detail the complex logistical planning required. Training of specialised dogs to the required standard also takes time and is of critical importance to the success of the operation. Following the aerial spreading of poison bait, up to five years is planned for locating and eradicating surviving rabbits, and the monitoring required to ensure that none were missed. The project may be completed much earlier if sufficient pressure is applied to the rabbit population.
Is it too late anyway – have the values of Macquarie already been lost?
The natural ability of the island’s ecosystem to restore itself is demonstrated by the revegetation apparent in fenced exclosure plots, and the return of grey petrels to breed on the island in 2000 following eradication of feral cats. Removal of the animals causing the current decline in the island’s values will, in time, enable the island to recover.
Have the full range of options from a reduction of rabbit numbers to partial control to eradication been considered?
Yes the options of control versus eradication have been considered in the eradication plan. Eradicating rabbits and rodents is the best way to protect Macquarie Island’s indigenous flora and fauna. It is also the most cost efficient and humane in the medium to long term. There have been successful pest eradications on other sub-Antarctic islands and the knowledge and experience gained in these operations will be applied to the Macquarie Island program.
In the short term, however, a control program for rabbits will help to reduce overall numbers and therefore impacts.
Isn't the rabbit population explosion part of a normal boom and bust cycle and won’t their numbers fall naturally as part of this cycle?
Rabbit numbers have been monitored on Macquarie Island since the 1970s. Climate and myxomatosis have influenced numbers over that time but there is not a demonstrated boom and bust cycle. An annual cycle is evident with numbers decreasing in winter months.
Are there any private providers of these pest control/eradication services and if so, have their advice and quotations for this program been sought?
A number of experts who have conducted pest eradications on islands around the world contributed to developing the eradication plan for Macquarie Island and their experience was invaluable. The draft plan was also reviewed by experts in this type of work, both within Australia and overseas. There may be opportunities for private contractors to provide services for this program.