Since the first sealing crew landed at Macquarie Island in 1810 a series of alien, or pest, animals were introduced to the island. Some with the hope they would benefit the men stationed to harvest seal and penguin oil, such as sheep, cats and wekas, and some unintentionally, like the rats and mice that jumped ship and found a new home. Three non-native bird species can be seen on Macquarie Island – Starling, Redpoll and Mallard. These birds were first observed on the island not long after they were introduced to New Zealand and Australia in the late 19th century, suggesting they migrated to the island independently.
By the end of the 1980’s most of the introduced animals – wekas, dogs, donkeys, goats, sheep, poultry – had either died off or been eradicated, but there remained large populations of feral cats, rabbits, black rats and mice. The cats were eradicated by 2000 but the rabbits, rats and mice were entrenched, their numbers noticeably increasing with the removal of the cats who had been their only predator on the island.
The island’s ecosystem was in crisis. Unchecked by predators rabbits caused landslips through burrowing into and over-grazing the ubiquitous tussock grasses and herbs, taking over seabird nesting burrows. Rats gorged on bird eggs and invaded nests across the island, and swam across to near-shore sea stacks on nest raids. Mice preyed on bird eggs and invertebrates, and stripped the flowers and seeds of the islands plant life.
The urgent need for action to halt the destruction caused by these pest was identified in the Macquarie Island World Heritage Area Management Plan 2006 which identified the removal of pest animals as one of the highest priorities for protecting and restoring the islands unique natural ecosystems. The extent of the damage caused by these pests is documented in the Macquarie Island in Danger report prepared by the University of Tasmania for the World Wildlife Fund (WWF). WWF went on to provide support for the Pest Eradication Project.
The result was the highly successful Macquarie Island Pest Eradication Project, carried out by the Tasmanian Parks and Wildlife Service with support from the federal government.
Begun in 2007 the project was the biggest of its kind ever undertaken, with the goal to eradicate the three pest species. Successful whole-island pest eradication programs had been completed before, most notably the New Zealand Department of Conservation’s Campbell Island rat eradication program, which cleared the Subantarctic island of the Norwegian rat by the end of 2005. Techniques from this program were adapted for use on Macquarie Island, which has become a success story in its own right.
The main strategies used in the Pest Eradication Project were aerial bait drops using helicopters, followed up by hunting and the use of rabbit and rat detection dogs. The first bait drops occurred in the winter of 2010, over a small section of the islands rugged south coast. The first round of bait drops were halted due to extreme bad weather. This baiting was successful in killing off large numbers of rabbits and rodents, but had a big impact on the islands seabirds. Rangers began to notice dead Northern and Southern Giant Petrels, Skuas and Kelp Gulls that had been feeding on the poisoned carcasses of dead rabbits. This secondary poisoning, as its known, was an identified risk of the project and after the 2010 season the project was reviewed to address the risk and reduce the impacts on seabirds, some of them listed as threatened or vulnerable to extinction. A government review made the point that “If rabbits and rodents are not eradicated, the local extinction of a number of burrowing petrel and perhaps eventually albatross populations from the Island is likely…. All experts consulted by the Review in session were of the view that, despite the risk of bird mortalities, the Eradication Program should be continued to address the severe and continuing degradation of Macquarie Island ecosystems and impacts on bird populations.”
The aerial baiting was completed in 2011 and while there continued to be some seabird deaths, the staff on the island were collecting as many rabbit carcasses as possible to reduce the risk of them being scavenged. The baiting was completed in July 2011, and by August hunters, with specially trained hunting dogs, were deployed on the island to track down and exterminate any surviving rabbits. In 2011, ABC’s Landline program did a special on the eradication project and its dedicated staff.
The last rabbit was killed in November 2011, and hunters continued to patrol the island into 2012-13 to ensure no rabbits resurfaced. In 2013 rodent detection dogs and their handlers arrived on the island to track down and eliminate any remaining rats and mice. They patrolled the island for a year, clocking up over 91,000kms walking all over the island.
The dogs employed in the project were all specially trained to detect rodents or rabbits, but to leave birds and other wildlife undisturbed. These hard-working dogs have become the public face of the Pest Eradication Project, with a series of stamps commemorating them being released by Australia Post in September 2015.
The 2014 Evaluation Report on the Pest Eradication Project states that the island’s ecosystem is already recovering following the removal of pests. The tussock grasses and herbs that were stripped by rabbits are re-growing in some eroded areas, and rangers and staff on the island have reported that there is an increase in the amount of spider webs and moths to be seen on the island. This is attributed to the removal of mice, which prey on moths, spiders and other invertebrates. It’s also been noted that some seabirds are recovering, with an increase in breeding attempts by Grey petrels. The observations of rangers and staff are essential in monitoring the effects of the eradication project, and the return of the islands ecosystem to a more balanced state.
The coming decades will show the true extent of the success of the Pest Eradication Project as seabirds, who are notoriously slow breeders, increase their presence on the island and fledge their young. The islands vegetation will slowly secure the slopes and soils from landslips and erosion as it re-grows unhindered by grazing. It will be fascinating to follow the progress of the islands environment, and how it changes and adjusts to being pest free. The Australian Antarctic Divisions’ website has regular updates on Macquarie Island, and includes current observations by staff of life on the island.