Watching an island transform Monitoring Macquarie Island after a massive intervention

IMAGE: ALEKS TERAUDS

In a time of rampant biodiversity decline, it’s heartening to consider that sometimes, ABOVE: Justine Shaw has watched the ebb and when we set our minds to it, grand things can be achieved. For that is exactly what flow of Macquarie Island’s natural wonder - from degraded World Heritage site, to a world-first happened on sub-Antarctic Macquarie Island where a multi-million dollar eradication island-wide predator control experiment. program saw the removal of rabbits, rats and mice in 2013. In the aftermath of species can do to an island ecosystem, it is also this effort, beautiful things are emerging. DrJustine Shaw from the University of turning out to be a wonderful case study and Queensland is leading a TSR Hub project seeking to learn from this experience and learning opportunity of what can be achieved if monitor how ecosystems respond. Here she explains what has happened. those invaders can be removed.

Far to the south of the Australian mainland biological structure has been under relentless Since the 1970s rabbits were controlled lies a large chunk of rock and soil known as attack from a several vertebrate invaders. through the introduction and continued Macquarie Island; it’s about 1500km from deployment of the myxomatosis virus. Feral The island was an important destination Hobart. So special is this place that it is on the cats were eradicated from Macquarie in 2000 for seal hunters who, over 180 years ago, World Heritage register as a geologically unique but it was always acknowledged this partial took cats to the island. Several decades later island with incredible aesthetic values. It is also solution wasn’t enough. The motivation for they released rabbits as a food source and a treasure trove of endemic and threatened cat eradication at the time was to ensure that unintentionally introduced rats and mice. All species. But the natural values of this World- burrowing petrel species did not go extinct on of these mammals made the island their home. Heritage island have been steadily eroding over the island, which was achieved. Rabbits, rats Over time these species pushed several native the past century as the island’s physical and and mice remained on the island. The rabbit species to the edge of extinction (and caused population went through another explosion in the extinction of at least two endemic bird the 2000s, due most likely to the eradication subspecies). And the rabbits had devastating impacts on the island’s cover of native vegetation recovery due to previous myxo success.of cats, a The reduction big breakthrough in the efficacy came of myxowith theand successful eradication of rabbits, rats and mice vegetationMacquarie (leadingIsland is tocurrently significant home soil to erosion). 12 EPBC- listed species; an endemic orchid, endemic in a program that commenced in 2013 through cushion plant, an endemic cormorant, 3 species a large-scale aerial baiting program that cost of burrowing petrel, four species of albatross, two species of giant petrel, two species of seal Key messages and the Antarctic tern. Many of these species were preyed upon by cats and rats, or indirectly The eradication of cats, rats, rabbits impacted through disturbance and habitat loss and mice from Macquarie Island by grazing rabbits, or changes in predation promises to transform the island’s pressure due to prey availability. Mice had a big ecological trajectory Monitoring the transformation will Grey petrel numbers are increasing following the spiders). impact on native invertebrates (and specifically removal of vertebrate pests. be important in guiding island- So, while Macquarie is yet another horrible eradication programs world-wide example of what a small group of non-native 4 Science for saving species LEFT: Grazing and burrowing rabbits removed vegetation resulting in substantial landslipping and erosion. RIGHT: Macquarie Island megaherb (dominated by Pleurophyllum hookeri), is now recovering following the acoustic recorders were deployed on Macquarie eradication of the rabbits. Island to survey the nesting burrowing petrels $24.8 million (that also included targeted Burrowing petrels are another good target for follow-up hunting). It was the largest, most monitoring. They were preyed upon by cats and that(for theresurveys first time). areas PhD-student where we have Jez Bird historic will ambitious and most expensive multi-species rats, and their nesting habitats were greatly data.undertake This will more enable field workus to estimatethis coming trends season in vertebrate eradication program ever attempted altered by rabbit grazing. While it has been relative abundance and the breeding success of in Australia. (The eradication was jointly assumed they will recover, we currently have funded by the Australian and Tasmanian state little data to support this. We do not currently of species monitoring, and examine known governments. Logistic support was provided by know if all species will respond the same and at sitesthese to petrels. identify Jez an will island-wide review existing approach methods to the Australian Antarctic Division.) the same rate. monitoring seabird presence and abundance. How has the island ecosystem responded to Skuas are another focus. This native predatory It is planned that all three PhD students will such a large-scale management intervention? bird ate rabbits, and some were poisoned be travelling south this summer to undertake during the eradication process (an anticipated out. I have assembled a team of collaborators; but unavoidable form of collateral damage of of Primary Industry, Parks, Water and scientistsI’ve been privilegedfrom other to universities lead a project (Melbourne, to find the project). Skuas also prey on burrowing Environmentmore field work. is a The key Tasmaniancollaborator Department in this Monash, UTAS), and Tasmanian state and petrels so there are some interesting and project. The project is also funded and supported federal government agencies. As part of this complex feedback interactions that are likely by the Australian Antarctic Science Program. effort we have recruited three PhD students to play out now that the cats, rats and rabbits who will examine different aspects of species are gone, and the prey available to skuas has and ecosystem recovery. Two are based within changed. It is of great relevance to managers what is happening on Macquarie Island is the TSR Hub at the University of Queensland, and threatened species scientists (locally and withoutNo-one can precedent. forecast I whatcan say, they however, will find there because is one is at the Institute of Marine & Antarctic globally) to determine the impacts of skua an enormous sense of excitement as the island’s Studies at the University of Tasmania. predation on threatened borrowing petrels. native ecosystems begin to recover after a century and a half of disruption. through a variety of historical sources and the whole. There is much greater value to the project than The first stage of the project has been to trawl What have we found so far? ‘Good’ responses on databases to collate records of where species simply documenting change and informing Preliminary work by PhD-student Melissa have been observed and studied. We are using management on Macquarie Island. Since the Houghton has shown that spiders are archival imagery and remote sensing to identify eradication, there have been other rodent increasing in abundance and distribution when and where rabbit grazing and burrowing eradications undertaken on sub-Antarctic South following the rodent eradication. had the greatest impacts on vegetation and threatened species habitat. This work is in conjunction with the Tasmanian Parks and eradication. As they are listed under the globalGeorgia island and Antipodes conservation islands, research and morecommunity are Grey petrels have increased since cat Wildlife Service. Agreement on the Conservation of Albatross & isproposed eagerly watchingfor Gough what and Marion happens Islands. on Macquarie The Petrels, there is much interest in determining Island in the hope that it will inform what we their population status and future trajectory. might do on other islands. is proposed in years to come, with the goal of New field data have been collected, and more tracking ecosystem change into the future. All As already mentioned many brown skuas For me the excitement of what is occurring on of these elements will assist in the development (several hundred) died during the eradication Macquarie Island is very personal as I have of an optimal long-term monitoring strategy process when they ate poisoned rabbit witnessed so much change on this unique for the island. Furthermore, this project will carcasses. But what happened afterwards? sub-Antarctic island over recent decades. In quantify the conservation return-on-investment Preliminary results collected by PhD-student my time I have seen the island inscribed as of the eradication program. The hope is that Toby Travers show a reduction in the breeding World Heritage; been present when cats were we can assist with decisions relating to island population and the reproductive output of eradicated; and then the rats, mice, and rabbits eradications all around the planet. the island skua population. This summer we removed. Now Macquarie is bouncing back will focus our efforts on investigating how the with a tremendous growth in its unique native brown skua diet has changed following rabbit vegetation. We are seeing the return of the grey for monitoring. Among these were some of the eradication, particularly to understand what the petrel, the recovery of endemic orchids, and invertebratesWe have identified found several on the ‘obvious’island (including candidates predation pressure may now be on burrowing who knows what’s more to follow… spiders). They were a major prey item of mice, petrels. and to a lesser extent rats, and rabbits greatly For further information transformed their habitats. They play a major The burrowing habit of the petrels makes then role in nutrient cycling on the island. Justine Shaw [email protected]

very difficult to monitor. Last summer, bio- 5