Why is Macquarie Island special?
Macquarie Island is an Australian sub-Antarctic island located 1500 kilometres southeast of Hobart, Tasmania. It is the only island in the world composed entirely of oceanic crust and rock from the Earth’s mantle. The island’s remote and windswept landscape supports vast congregations of wildlife, and was inscribed on the World Heritage List in 1997, in recognition of its geological significance and outstanding natural beauty.
Macquarie Island is one of only a very few islands in the Pacific sector of the Southern Ocean where fauna in the region can breed. Around 3.5 million seabirds and 80,000 elephant seals arrive on the long, thin strip of mountainous terrain each year to breed and moult. Fur seals are re-establishing populations on the island after nearly being exterminated by commercial sealing operations in the early 19th century.
The island was declared a Wildlife Sanctuary in 1933 and designated as a State Nature Reserve in 1972, in recognition of its important sub-Antarctic flora and fauna; including several species not found elsewhere—such as the royal penguin. In 1977 it became a UNESCO Biosphere Reserve and in 2002 was listed on the Register of Critical Habitat. It is the only island under Australian jurisdiction that provides a breeding habitat for the wandering albatross and the grey-headed albatross, both of which are considered as vulnerable to extinction.
These numerous designations reflect the importance of the reserve’s natural values, and why it’s necessary to protect them for future generations.
The Tasmanian Government’s Parks and Wildlife Service (PWS) manages the island as a nature reserve, and manages its World Heritage values on behalf of the Australian Government. The Australian Government maintains an Antarctic Division research station and a Bureau of Meteorology weather station on the island.
What problems are caused by introduced species?
In recent years there has been a significant increase in damage to vegetation caused by rabbits on Macquarie Island. Vegetation communities are a critical part of the Macquarie Island ecosystem as they protect soil and rocks from weathering, stabilise steep slopes and provide habitat for invertebrates and burrow-nesting seabirds. In 2006 landslides caused at least partially by rabbit grazing, buried penguins and damaged visitor boardwalks.
Rodents have a significant impact on the island, as they eat plant foliage, flowers and seeds, which prevents seedling recruitment. As there are no trees or shrubs on the island, all species must breed on or in the ground, where they can fall prey to ship rats. Rats eat the chicks and eggs of burrow-nesting petrels. Mice and rats also prey on invertebrate species.
Was the eradication of cats responsible for the increase in rabbit numbers?
No, not solely. A combination of factors was involved. These included the removal of a major predator, feral cats, resistance to the myxoma virus leading to reduced effectiveness within the island's rabbit population, and the unavailability of new stocks to continue spreading the virus.
What does the eradication project involve?
The eradication of rabbits, rats and mice on Macquarie Island should be seen as three specific eradications being conducted concurrently, in order to maximise the efficient use of resources. The proposed techniques are based on the successful eradication of introduced species on other islands and on the characteristics of each of the three target species.
In the first phase, helicopters will spread pellet baits containing the toxin brodifacoum. Global Positioning System (GPS) units in the helicopters ensure an accurate bait coverage, which should eradicate all of the rodents and remove a high proportion of rabbits. This methodology has successfully eradicated rodents from many islands around the world.
After aerial baiting, field teams will follow up on the ground eliminating surviving rabbits by shooting, fumigating and trapping them. Dogs will be used to indicate where rabbits are surviving, and are considered critical in locating rabbits in the rugged terrain of Macquarie Island.
Work undertaken on the project to date includes:
- • An automatic weather station was established on the southern plateau in 2007 to assist in determining weather patterns – an important factor for planning helicopter flights for spreading poison baits
- • Trials testing the effectiveness of bait pods and the effects of helicopters flying over penguin rookeries were conducted in 2007 and 2008. Non-toxic baits have also been trialled to assess weathering characteristics and palatability of the bait, and whether non-target species are likely to be at risk from the bait
- • 28 plots around the island were fenced to protect plant species that may not recover from severe rabbit grazing
- • Dogs have been trained to detect rabbits and to ignore native animals on Macquarie Island
- • Portable huts have been fitted out for field staff accommodation
How has the poison been selected?
The use of poisons is an accepted practice in dealing with pest species, as no other techniques have proven successful in eradicating rodents on large sub-Antarctic islands. Various toxins were considered and brodifacoum was identified as being the most suitable. The toxin is the same as that used in some rat poisons that are widely available for domestic use.
Will native animals be affected by aerial baiting?
The need to minimise impacts on native species has been an important consideration in all planning. The baiting will be conducted in winter when most of the native animals have left the island, thus avoiding or minimising effects on their populations.
However, some mortality of non-target species was expected as this has been the case in other island eradication programs. An Environmental Impact Statement was prepared to assess the likely impact of the project and this identified that some bird species would be at risk from primary poisoning as a result of ingesting baits and secondary poisoning from scavenging on dead animals that have eaten the baits. Of the bird species native to Macquarie Island, 80 per cent were unaffected by baiting.
Trials conducted on the island with non-toxic baits showed that most native bird species are not interested in the pellets, although some gulls may consume them.
Eradicating rabbits and rodents will vastly improve conditions for native species, and at least 28 native bird species are expected to increase in population, following a successful pest eradication.
When aerial baiting occurs teams will search for and remove poisoned carcasses following baiting. This is expected to result in fewer deaths among non-target species that scavenge dead animals.
When will the aerial baiting occur?
The winter months are the best time to conduct aerial baiting for the following reasons:
- • Many of the native animals depart the island for winter
- • Rabbit and rodent numbers decline during winter due to a lull in breeding and higher mortality, meaning there are fewer animals to target and fewer need to be killed
- • There is a greater chance the rabbits and rodents will eat the baits, as there is less vegetation available for them to consume at this time of year
- • It avoids the summer tourist season so tourism operators will not be affected.
How long will the eradication project take?
The aerial bait drop was scheduled for winter 2010. Unfortunately, adverse weather conditions prevented completion of the aerial baiting and it was completed in winter 2011. After aerial baiting, three years has been allocated for the eradication of surviving rabbits. Once the last known rabbit has been removed, a monitoring period of two years will commence to check thoroughly for any indications of rodents or rabbits surviving.
Is it too late – have the values of Macquarie Island been lost?
The natural ability of the island ecosystem to restore itself has been demonstrated by the revegetation evident within fenced exclosure plots, and the return of grey petrels to breed on the island in 2000 following eradication of feral cats. Removal of the pest animals that are causing the decline in the island’s values will, in time, give the island environment the conditions needed for recovery.
Will the island need to be revegetated once rabbits are removed?
Macquarie Island has harsh growing conditions for plants and recovery of some vegetation communities may take decades.
Exclosure plots constructed on the island since the 1960s have demonstrated that the rate of vegetation recovery can be high in favourable sites. Because of that recovery, no revegetation activity is currently proposed. (see a series of photos of an exclosure plot constructed in 2006 - PDF 786Kb
What if this doesn’t work – what are the other options?
If the project is unsuccessful in eradicating any or all of the three target species, future management may involve control of rabbits to low numbers and possible future eradication attempts for rodents. Before this could be considered, the lessons learnt from this project would need to be carefully assessed along with the ongoing development of eradication techniques.
Eradicating rabbits and rodents is the best way to protect Macquarie Island’s native flora and fauna and World Heritage values. There have been successful pest eradications on other islands, and this project is benefiting from that experience. The project is very ambitious, but the conservation gains from a successful eradication are immense.