Rabb¡t Scourge Strips Macquarie lsland Bare

Corey Bradshaw finds that rabbits are wreaking havoc on Macquarie lsland, and says it's time they were eradicated.

twas goodtobe back on Macquarie but sad, dirby clumps of dried and mafted Island, the oft-called "Green Sponge" vegetation in which turmels had been and most southerlypart of Austualia, dug ttroughout. At first I couldn't quite after an 18-month absence. I had believe the change that had occurred, returned to continue my field work and then the reason for this devastation examining the foraging ecology and bor¡nded ahead of me and up the slope behaviour of southern elephant seals - the intooduced . ØS, Ja¡lFeb 2003,pp.24-28) with two Most Australiars are familiar with the new PhD students about to st¿rt their problems that introduced rabbits have projects. caused in our country - the destuction Our research activities are varied, but of native vegetation, the fouling of agri- probably the most important are the cultural areas, and the maintenance of daily searches ofthe northern beaches inkoduced predators like foxes and cats. for seals returning from their at-sea Probablyfew of us, however, axe aware migrations. The characteristic westerþ that intooduced rabbits have been a long- problem winds were blowing across the isthmus standing for the more remote A juvenile southern elephant seal sleeps at about 30 knots that December and seemingly "pristine" comers of the among rabbit-denuded tussock grasses and moming, and the beaches were littered globe. patches of annual meadow grass. with recently weaned elephant seals, Although I had come to be rather king and gentoo penguins, giant petrels familiar with the sight of rabbits on 1810 and soon became a hot spot for the and subantarctic skuas. Macquarie Island since my first visit in harvesting of seals andpenguirs forpelts I was walking south from the 1999, I had never before noticed such and oil. Australian Antarctic Program's base blatant devast¿tion of the life. What Inscribed as a World Heritage Area toward a beach we call Cabbage Cove had happened in the past few years? primarily for its unique geologr in 1997, when something odd struck me. The Were other areas of the island affected the island has seen ahost of human and cabbage were gone! equally? Was anything being done to non-human visitors, among them the In less thart 2 years the hjllsides of control these pests? deliberate and accident¿l introductiors Cabbage Cove, so named for the lush Macquarie IsÌand is ayoung island in of rabbits, cats, weka, rats, mice and and dense stand of Macquarie Island terms of its geological, ecological and many more vertebrate, invertebrate and cabbage usually growing there, had been anthropological history. This 12,800 plant species. Although some of these stuipped bare. Even the tall and robust hectare "rock" in the middle of the species have nowbeen eradicated, such stands of tussock grass were nothing Southern Oceanwas orùy discovered in as weka and most recently cats, others remain a signif.cant problem. Rabbits were first introduced during the 1870s by the New ZeaLand sealing company Elders as a source of fresh food for the seal harvesters. $ rapidly e4panding and successfulpoprfation of rabbits soon covered mobt of the Sllcn- long island. It is interesting and fright- ening to note that Macquarie Island had been free ofverbebrate herbivores before Before and after: rabbit grazing cuts down the hookeri. the introduction of rabbits.

May 2oo4t sftiëîîte | 23 Healthy Macquarie lsland cabbage.

reached pre-control numbers. During thattime, research has demonshated a number oftuends. The large decline immediately followingthe first application of myxoma virus res-ilted in more luxurious growth of the existing vegetation, although some plant qpecies did not recover for another decade or so. The charismatic native tussock grass and the megaherb Plez- rophgllum hookeri both recovered as rabbit numbers decreased, suggesting that these plant species were once more widespread on the island. The Macquarie Island cabbage showed much improvement as well, but it is the most sersitive of the larger plant qpecies to rabbit grazng. Thus my imme diate observation in Cabbage Cove

seemed to s u ggest a recent and relatively large increase in rabbit numbers since my last visit in 2002. Feral cats and rabbits had an inter- esting relatiorship on Macquarie Island, and the eradication ofthe cat popula- tion by 2002 may shed some light on Lush growth of Macquarie lsland cabbage and tussock grass (top) have been stripped bare (below) by rabbits. the recent increases in rabbit numbers. Cats were present on the island from Seal a¡rd penguin hawesting ceased However, it wasn't until the late 1970s, the 1820s onwards, so the introduction altogether in 1919, and it wasn't until when the population was estimated at of rabbits in the 1870s provided a rich 1948 that the frst year-round Australian 150,000, tlntthe intuoduction of myxoma new food resource. Indeed, an analysis National Antarctic Research Expedition virus and its invertebrate vector, the of cat diet revealed a rapid switch to base was established. It was apparent European rabbit flea" resulted in declines rabbits upon their reintroduction, with to the visiting scientists that rabbits and ofthe rabbit population by an order of fewer mice and native sea birds taken the other feral species were doing exces- magnitude. However, despite the nearly as a result. sive damage to the island's sensitive annual reintroduction of the m)¡r(oma Withthe intuoduction of the m)Ð(oma plant biota, so an eradication program virus combined with opportunistic virus, the number of sick and dying based on shooting was eventually set in shooting since 1978, the rabbit popr-rla- rabbits again increased the proportion of motion in the late 1960s by the cslRo, tion persists today. rabbits eaten by cats. However, the Australian Antarctic Division and the Although the rabbit popr-rlation has benefit of more dying rabbits was short- Tasmanian Department of Primary fluctuated in the years since controls lived - as soon as the major rabbit Industry. began, the population has never again decline had occurred, cats resumed z¿ I Sftilëîïtê rMay 2oo4 Corey Bradshaw with an endemic coastal cushion plant (Azorella macquariensis) growing A rabbit carcass picked over by subantarctic above the reach of rabbits. skuas - a common site on Macquarie lsland. eating many of the more susceptible possible that the enhanced skua popu- scavenger-predators, and an associated burrow-nesting bird species such as Iation may be restricting the recovery of reduction in sea bird mortality. Antarctic prions, fairy prions, sooty the rarer and more-sensitive sea birds. But rabbits may also serve some shearwaters and white-headed petoels. On one recent excursion beside a small beneflcial functiors within this sensitive Although we can now feel good about lake on the plateau where hundreds of ecosystem. It appears that many vascular the eradication of cats and the associ- Antarctic prions breed I noticed quite a plant species have beneflted from the ated reduction in sea bird mortality, few prion remairs from skua kills. Thus, presence of rabbits due to selective rabbits still continue to change the aprobable outcome of the eradication of grazing of more-palatable competing biological community. rabbits on Macquarie Island will be re- species, changes in the cover of domi- Approximately 4 years after the rabbit distribution and reduction in these nant species, variation in the water table control began, the number of subantarctic skua breeding sites decreased by 54% on the plateau but increasedby 17%in coastàl areas. These results are likely to be the result of a rediskibution of breeding in relation to the more-available prey resources in coastal areas, such as penguins, eggs and dead seals, after the rabbits began to decline in the higher altitudes of the island. It aJso appeared to me that there has been a steady increase in the number of skua on Macquarie Island since I first started coming here in 1999. It isn't unusual to see skuas busily ripping rabbit carcasses to shreds, chasing young rabbits, or even picking aparl rabbits dying from myxoma virus. Skuas are aJso opporh-rnistic hr¡nters of the smaller A weakened rabbit infected with myxoma virus. Vegetation on Macquarie lsland burrowing sea bird species, so it is recovered when myxoma virus was first introduced.

May 2oo4l sti1ëi¡ite | 25 Subantarctic skuas feeding on a recently killed rabbit. Skuas may need to predate greater numbers of burrowing sea birds if rabbit populations were eradicated from Macquarie lsland.

and increased opportunities for these colonisation by these non-natives. $2.5 million, 19 people, hro ships, five species to colonise disturbed axeas (e.9. Despite the odd beneflt that rabbits helicopters and more than 120 tonnes burrowing sites and terrestial scrapes). may engender to some plant and animal of cereal pellets laced with rat poison. The restriction of tussock grass may species, either directly or indirectly, I An eradication of rabbits and rats also provide an inadvertent reduction in believe most people would agree that from Macquarie Istand has been contem- the distribution of ship rats that use it rabbits have overstayed their welcome plated for many years, but now with the as aprimary habitat. Ship rats are oppor- on Macquarie Island. But where do we success story of Campbell Island I tunistic predators of many burrow- go from here? believe the time is ripe for action. nesting sea birds, so an eradication of As I write this, the trvo Tasmanian Rabbits could be dispatched in much rabbits may result in an increase in both Parks and Wildlife Service rangers are the same marìner as the rats on Camp- tussock and rat distribution that may actively spreading the myxomavirus and bell Island by using cereal-based baits Iead to increased mortality for the more shooting rabbits in high-dersity areas, containing the anticoagulant brodifa- isolated sea bird colonies. as they've done since the 1970s, but coum. This, along with intensive At several other isolated clearly these actions are irsuffrcient. shooting, the maintenance of myxoma subantarctic islands where rabbits also kr 200 1 the N ew Zealand govemment virus and several years of follow-up occur, such as Kerguelen Island and completed one ofthe world's mostambi- monitoring cor:ld bring aboutthe end of Marion Island, grazing has impeded the tious pest eradication projects on Camp this long-term feral species. plant qpecies spread of inhoduced such bell Island T00lcnsouth of NewZealand. It's nowup to the Ausúalianpeople to as the common dandelion and turf This 11,300 hectare island, which was raise the necessaxy funds for such an grass. These weed species do not occur discovered around the same time as endeavour, and I believe that aterting on Macquarie Island, although a Macquarie Island, was home to a large more Australians about the issue is the nur-nber of other inhoduced plants have population of introduced Norway rats first step. Perhaps for the relatively managed to establish themselves, that had been resporsible for the extinc- modest sum of $3-4 million we could grass including annual meadow and tion of at least three land-bird species witress the eradication of the remaining mouse-ear chickweed. However, the and the near-eradication of many sea major vertebrate pests.from this impact of introducedplants is relatively birds. subantarctic jewel in Australia's crown. small compared with other islands else- Now, several years after the project, where. There is no evidence that they the eradication of rats on Campbell Corey Bradshaw completed this research while working as a poldoctoral research fellow w¡th the Antarctic W¡ldlife are displacing native vegetation, and Island is touted as a mqjor conservation Research Un¡t of the University of Tasman¡a's School of an eradication of rabbits would result success. However, its success r¡/as due Zoology. Last month he commenced work as a Senior Research Fellow w¡th Charles Damin LJn¡versity's Key Centre in fewer disturbed sites available for to acommittedinveshnent of more than for Tropi€l Wildlife Management.

26 I stilëîite tMay 2oo4