Turning the Tide: The Eradication of Invasive Species

Proceedings of the International Conference

On Eradication of Island Invasives

Edited by C. R. Veitch and M. N. Clout

Occasional Paper of the IUCN Species Survival Commission No. 27

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Contents Preface Turning the tide of biological invasion: the potential for eradicating invasive species .................................................1

M. N. Clout and C. R. Veitch

Keynote Address Today Tiritiri Matangi, tomorrow the world! Are we aiming too low in invasives control?........................................4

D. Simberloff Papers Cat eradication on Hermite Island, Montebello Islands, Western Australia ................................................................14

D. A. Algar, A. A. Burbidge, and G. J. Angus Eradication of introduced Bactrocera species (Diptera: Tephritidae) in Nauru using male annihilation

and protein bait application techniques ..............................................................................................................19 A. J. Allwood, E. T. Vueti, L. Leblanc, and R. Bull

Man-made marinas as sheltered islands for alien marine organisms: Establishment and eradication of an alien invasive marine species.........................................................................................................................26

N. Bax, K. Hayes, A. Marshall, D. Parry, and R. Thresher The eradication of alien mammals from five offshore islands, Mauritius, Indian Ocean ............................................40

B. D. Bell The eradication of possums from Kapiti Island, New Zealand....................................................................................46

K. P. Brown and G. H. Sherley The impact of rabbit and goat eradication on the ecology of Round Island, Mauritius ...............................................53

D. J. Bullock, S. G. North, M. E. Dulloo, and M. Thorsen Introduced mammal eradications for nature conservation on Western Australian islands: a review...........................64

A. A. Burbidge and K. D. Morris Habitat refuges as alternatives to predator control for the conservation of endangered Mauritian birds.....................71

S. P. Carter and P. W. Bright Control of invasive plants on the Poor Knights Islands, New Zealand........................................................................79

G. J. Coulston Eradication planning for invasive alien animal species on islands – the approach developed by the

New Zealand Department of Conservation ........................................................................................................85 P. L. Cromarty, K. G Broome, A. Cox, R. A. Empson, W. M. Hutchinson, and I. McFadden

Eradication of buffel grass (Cenchrus ciliaris) on Airlie Island, Pilbara Coast, Western Australia............................92 I. R. Dixon, K. W. Dixon, and M. Barrett

Eradications of invasive species to restore natural biological diversity on Alaska Maritime National Wildlife Refuge ................................................................................................................................................102

S. E. Ebbert and G. V. Byrd Control and eradication of the introduced grass, Cenchrus echinatus, at Laysan Island, Central Pacific Ocean ......110

E. Flint and C. Rehkemper The eradication of Rattus rattus from Monito Island, West Indies............................................................................116

M. A. García, C. E. Diez, and A. O. Alvarez Changes in bird numbers on Tiritiri Matangi Island, New Zealand, over the period of rat eradication ....................120

M. F. Graham and C. R. Veitch Spartina anglica eradication and inter-tidal recovery in Northern Ireland estuaries. ................................................124

M. E. R. Hammond and A. Cooper Eradication of feral goats and pigs and consequences for other biota on Sarigan Island,

Commonwealth of the Northern Mariana Islands.............................................................................................132 C. C. Kessler

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The response of herbaceous vegetation and endemic plant species to the removal of feral sheep from Santa Cruz Island, California ...................................................................................................................141

R. C. Klinger, P. Schuyler, and J. D. Sterner Alien plant and animal control and aspects of ecological restoration in a small ‘mainland island’:

Wenderholm Regional Park, New Zealand. .....................................................................................................155 T. G. Lovegrove, C. H. Zeiler, B. S. Greene, B. W. Green, R. Gaastra, and A. D. MacArthur

Eradicating invasive plants: Hard-won lessons for islands........................................................................................164 R. N. Mack and W. M. Lonsdale

Eradication of Pacific rats (Rattus exulans) from Whenua Hou Nature Reserve (Codfish Island), Putauhinu and Rarotoka Islands, New Zealand. ...............................................................................................173

P. J. McClelland Alien mammal eradication and quarantine on inhabited islands in the Seychelles....................................................182

D. Merton, G. Climo, V. Laboudallon, S. Robert, and C. Mander Eradication of rats and rabbits from Saint-Paul Island, French Southern Territories ................................................199

T. Micol and P. Jouventin Cat eradication and the restoration of endangered iguanas (Cyclura carinata) on Long Cay,

Caicos Bank, Turks and Caicos Islands, British West Indies ...........................................................................206 N. Mitchell, R. Haeffner, V. Veer, M. Fulford-Gardner, W. Clerveaux, C. R. Veitch, and G. Mitchell

Comparison of baits and bait stations for the selective control of wild house mice on Thevenard Island, Western Australia .............................................................................................................................................213

D. Moro The eradication of the black rat (Rattus rattus) on Barrow and adjacent islands off the north-west

coast of Western Australia................................................................................................................................219 K. D. Morris

Eradication of introduced Australian marsupials (brushtail possum and brushtailed rock wallaby) from Rangitoto and Motutapu Islands, New Zealand.......................................................................................226

S. C. Mowbray An attempt to eradicate feral goats from Lord Howe Island......................................................................................233

J. P. Parkes, N. Macdonald, and G. Leaman Red mangrove eradication and pickleweed control in a Hawaiian wetland, waterbird responses,

and lessons learned ...........................................................................................................................................240 M. J. Rauzon and D. C. Drigot

When is eradication of exotic pest plants a realistic goal? ........................................................................................249 M. Rejmánek and M. J. Pitcairn

Management of indigenous and alien Malvaceae on islands near Perth, Western Australia .....................................254 E. Rippey, J. J. Rippey, and N. Dunlop

Practical concerns in the eradication of island snakes ...............................................................................................260 G. H. Rodda, T. H. Fritts, E. W. Campbell III, K. Dean-Bradley, G. Perry, and C. P. Qualls

An ecological basis for control of the mongoose Herpestes javanicus in Mauritius: is eradication possible? ..........266 S. S. Roy, C. G. Jones, and S. Harris

Eradication of feral pigs (Sus scrofa) on Santa Catalina Island, California, USA.....................................................274 P. T. Schuyler, D. K. Garcelon, and S. Escover

Eradication of potentially invasive plants with limited distributions in the Galapagos Islands.................................287 M. C. Soria, M. R. Gardener, and A. Tye

Island conservation in north-west Mexico: a conservation model integrating research, education and exotic mammal eradication ........................................................................................................................293

B. R. Tershy, C. J. Donlan, B. S. Keitt, D. A. Croll, J. A. Sanchez, B. Wood, M. A. Hermosillo, G. R. Howald, and N. Biavaschi

A history of ground-based rodent eradication techniques developed in New Zealand, 1959–1993..........................301 B. W. Thomas and R. H. Taylor

Early detection of invasive weeds on islands ............................................................................................................311 S. M. Timmins and H. Braithwaite

Eradication of rabbits and mice from subantarctic Enderby and Rose Islands ..........................................................319 N. Torr

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Interactions between geckos, honeydew scale insects and host plants revealed on islands in northern New Zealand, following eradication of introduced rats and rabbits ..................................................329

D. R. Towns A strategy for Galapagos weeds ................................................................................................................................336

A. Tye, M. C. Soria, and M. R. Gardener Eradicating Indian musk shrews (Suncus murinus, Soricidae) from Mauritian offshore islands...............................342

K. J. Varnham, S. S. Roy, A. Seymour, J. Mauremootoo, C. G. Jones, and S. Harris Eradication of Norway rats (Rattus norvegicus) and house mouse (Mus musculus) from

Browns Island (Motukorea), Hauraki Gulf, New Zealand................................................................................350 C. R. Veitch

Eradication of Norway rats (Rattus norvegicus) and house mouse (Mus musculus) from Motuihe Island, New Zealand...........................................................................................................................353

C. R. Veitch Eradication of Pacific rats (Rattus exulans) from Fanal Island, New Zealand. .........................................................357

C. R. Veitch Eradication of Pacific rats (Rattus exulans) from Tiritiri Matangi Island, Hauraki Gulf, New Zealand ...................360

C. R. Veitch Eradication of alien plants on Raoul Island, Kermadec Islands, New Zealand .........................................................365

C. J. West Removing cats from islands in north-west Mexico ...................................................................................................374

B. Wood, B. R. Tershy, M. A. Hermosillo, C. J. Donlan, J. A. Sanchez, B. S. Keitt, D. A. Croll, G. R. Howald, and N. Biavaschi

The evolution and execution of a plan for invasive weed eradication and control, Rangitoto Island, Hauraki Gulf, New Zealand..............................................................................................................................381

S. H. Wotherspoon and J. A. Wotherspoon Impacts and control of introduced small Indian mongoose on Amami Island, Japan................................................389

F. Yamada It’s often better to eradicate, but can we eradicate better?.........................................................................................393

E. S. Zavaleta Abstracts Removing a diverse suite of invasive threats to recover an endangered Hawaiian bird species

and its dry forest habitat.......................................................................................................................................406 P. C. Banko, S. Dougill, L. Gold, D. Goltz, L. Johnson, P. Oboyski, and J. Slotterback

Introduced Neotropical tree frogs in the Hawaiian Islands: Control technique development and population status............................................................................................................................................406 E. W. Campbell, F. Kraus, S. Joe, L. Oberhofer, R. Sugihara, D. Lease, and P. Krushelnycky

Tackling tussock moths: strategies, timelines and outcomes of two programmes for eradicating tussock moths from suburbs of Auckland, New Zealand.....................................................................................407 J. R. Clearwater

Recovery of invertebrate populations on Tiritiri Matangi Island, New Zealand following eradication of Pacific rats (Rattus exulans) ............................................................................................................................407 C. J. Green

Restoration of tree weta (Orthoptera: Anostostomatidae) to a modified island.........................................................407 C. J. Green

Control of cats on mountain “islands”, Stewart Island, New Zealand.......................................................................408 G. A. Harper and M. Dobbins

The status of invasive ant control in the conservation of island systems...................................................................408 P. D. Krushelnycky, E. Van Gelder, L. L. Loope, and R. Gillespie

The effectiveness of weeded and fenced ‘Conservation Management Areas’ as a means of maintaining the threatened biodiversity of mainland Mauritius...............................................................................................408 J. R. Mauremootoo, C. G. Jones, W. A. Strahm, M. E. Dulloo, and Y. Mungroo

Preparation for the eradication of Norway rats (Rattus norvegicus) from Campbell Island, New Zealand...............409 P. J. McClelland

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Island quarantine – prevention is better than cure .....................................................................................................409 P. J. McClelland

The role of parasitoids in eradication or area-wide control of tephritid fruit flies in the Hawaiian Islands...............410 R. H. Messing

Response of forest birds to rat eradication on Kapiti Island, New Zealand...............................................................410 C. Miskelly and H. Robertson

Sustained control of feral goats in Egmont National Park, New Zealand..................................................................410 D. M. Forsyth, J. P. Parkes, D. Choquenot, G. Reid, and D. Stronge

Pacific rats: their impacts on two small seabird species in the Hen and Chickens Islands, New Zealand.................411 R. J. Pierce

Seabird re-colonisation after cat eradication on equatorial Jarvis, Howland, and Baker Islands, USA, Central Pacific......................................................................................................................................................411 M. J. Rauzon, D. J. Forsell, and E. N. Flint

Direct and indirect effects of house mice on declining populations of a small seabird, the ashy storm-petrel (Oceanodroma homochroa), on Southeast Farallon Island, California, USA......................................................412 K. L. Mills, P. Pyle, W. J. Sydeman, J. Buffa, and M. J. Rauzon

Managing pest mammals at near-zero densities at sites on the New Zealand mainland............................................412 A. Saunders

Control of feral goats (Capra hircus) on Santa Catalina Island, California, USA.....................................................412 P. T. Schuyler, D. Garcelon and S. Escover

Control of the invasive exotic yellow crazy ant (Anoplolepis gracilipes) on Christmas Island, Indian Ocean .........413 D. J. Slip

Preventing rat introductions to the Pribilof Islands, Alaska, USA ............................................................................413 A. L. Sowls and G. V. Byrd

Ecological restoration of islands in Breaksea Sound, Fiordland, New Zealand ........................................................414 B. W. Thomas

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The effects of alien invasive species on biodiversity havebeen described as “immense, insidious and usually irre-versible” (IUCN 2000).

There is no doubt that invasive species can cause severeeconomic and ecological damage (Mack et al. 2000). Theymay soon surpass habitat loss as the main cause of eco-logical disintegration globally (Vitousek et al. 1997,Chapin et al. 2000) and are probably already the main causeof extinctions in island ecosystems. The breaching ofbiogeographic boundaries by the widespread, recent hu-man transport of species has caused rapid and radicalchange in biological communities, including multipleextinctions. To minimise further extinctions and other eco-logical changes, the most important priority is to reducethe risks of new invasions. After prevention, the next pri-ority is to eradicate existing invasive species, where this ispossible. These aims are embodied in the United NationsConvention on Biological Diversity, which states that par-ties to this convention should “ prevent the introductionof, control or eradicate, those alien species which threatenecosystems, habitats or species”.

Extinction is irreversible, but there is a growing realisa-tion that biological invasions themselves can sometimesbe reversed. With good planning, adequate techniques andsustained effort, it is now possible to eradicate many typesof invasive species, especially in the early stages of aninvasion, or where a population is confined to an island orlimited habitat.

Turning the tide of biological invasion by eradicating in-vasive species can yield substantial benefits for biodiversityconservation, by raising opportunities for ecological res-toration and the re-introduction of threatened species. Itcan also yield major economic benefits, by permanentlyremoving the cause of damage to crops, livestock or na-tive biodiversity, and obviating the need for costly per-petual control. Where feasible, eradication is typically moreenvironmentally sound and ethically acceptable than long-term control. Sustained control may involve the perpetualuse of toxins, trapping or shooting, and can entail moreenvironmental risks and many more animal deaths than a

brief eradication campaign. In this context, the recent suc-cessful action by animal ethicists to prevent the eradica-tion of an incipient population of grey squirrels (Sciuruscarolinensis) in Italy is a particularly sad example(Genovesi and Bertolino 2001). Many more squirrels willundoubtedly die in control attempts in the years to comethan would have been killed in eradication of the initialpopulation. Likely consequences of this invasion (as withso many others) are damage to crops and natural ecosys-tems and the decline of native species.

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There is a well-accepted set of conditions which must bemet for the eradication of any population (Bomford andO’Brien 1995). These standard conditions for success areproper planning, a commitment to complete, putting theentire population of the target species at risk, removingthem faster than they reproduce, and preventing re-inva-sion. Additional conditions, which are often necessary andalways desirable, are support from local people and anability to demonstrate the benefits of the eradication pro-gramme.

It is easiest to meet the necessary eradication conditionsfor isolated, small populations of species with low repro-ductive rates and no dormant life stages. Not surprisingly,the most notable successes to date have therefore involvedthe eradication of vertebrates (especially mammals) fromisolated islands. Over the past 20 years, as techniques andconfidence have improved, it has proved feasible to eradi-cate even quite small vertebrates from larger and largerislands. For example, in New Zealand, Norway rats (Rat-tus norvegicus) are now being eradicated from islands upto 11,000 ha in area. This is more than three orders ofmagnitude larger than the islands from which this specieswas first eradicated c. 40 years ago (Fig. 1).

It is fortunate that invasive mammals are among the easierspecies to eradicate, because they are also among the mostecologically damaging, especially on islands. Manyextinctions of vulnerable birds, reptiles, and plants havebeen attributed to introduced mammals (Atkinson 1989),so the increasing ability to eradicate them is especiallysignificant.

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M. N. Clout1 and C. R. Veitch21 Centre for Invasive Species Research, SGES, University of Auckland, Private Bag 92019,

Auckland, New Zealand. E-mail m.clout@auckland.ac.nz 2 48 Manse Road, Papakura,New Zealand.

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Turning the tide: the eradication of invasive species

2

Established populations of plants, insects and other spe-cies with dormant life stages (eg. soil seedbanks) and highintrinsic rates of increase present more of a challenge foreradication, even in isolated populations. Typically, theeradication of plant populations involves a long campaign,involving the sustained removal of individuals before theyset seed. In the longer term these species will be just asdamaging to ecosystems as the more rapid and visibleimpact of many mammals.

In many situations, the feasibility of eradication will alsobe affected by risks to non-target species. This may pre-vent the use of certain techniques and limit the use of oth-ers. In some situations the risks to non-target species (in-cluding livestock, pets, crops and people) currently pre-cludes the attempted eradication of some invasive species.However, some non-target deaths are acceptable if eradi-cation of the invasive species is achieved and recovery ofthe affected non-target species is likely to be rapid. Forexample, in the course of the eradication of brushtail pos-sums (Trichosurus vulpecula) from Kapiti Island, NewZealand, 181 birds were killed in traps, 39% of which werekereru (Hemiphaga novaeseelandiae) (Cowan 1992). Fol-lowing the possum eradication (and subsequent eradica-tion of rats by poisoning), the forest recovered substan-tially and kereru abundance rose up to six fold (Veltman2000).

A factor that often affects the feasibility of any eradica-tion is the dispersal abilities of the weed or pest speciesconcerned. This affects re-invasion potential and may dic-tate continued vigilance even when the original popula-tion has been eradicated. For example, plants that are dis-

persed by birds or wind are more likely to re-invade anisolated island than those that depend on browsing mam-mals, gravity, explosion, or water dispersal. Human trans-port remains the most likely re-invasion pathway for mostinvasive species, emphasising the fact that prevention ofinvasion is of the utmost importance.

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There have been substantial recent advances in our abilityto eradicate invasive species, exemplified by the increas-ing size of islands from which invasive vertebrates suchas rodents have been eradicated (Fig. 1). We can antici-pate more successful eradications of invasive vertebratespecies, as existing technology and approaches are applied.Eradications of invertebrates and plants may pose greaterchallenges and require more sustained campaigns, but thegeneral principles remain the same and there have beennotable successes, some of which are described in thisvolume.

A topic which merits greater attention when planningeradications is that of ecosystem response to species re-movals (Zavelata et al. 2001). There may be unexpected(and sometimes unwanted) consequences of eradications,such as the ecological release of invasive plants when anintroduced herbivore is removed, or irruptions of prey spe-cies after the removal of a predator. Such effects need tobe borne in mind when planning eradications. Knowledgeof the ecological relationships of invasive species is a keyprerequisite when planning their removal from an ecosys-tem. These relationships raise opportunities as well as risks:for example it is possible to remove invasive prey species(e.g. rodents) and their introduced predators (e.g. cats) ina single poisoning operation, through deliberate second-ary poisoning of the predators via their toxic prey.

As more eradications are attempted worldwide, it is in-creasingly important that lessons are learned from eachand every one of these attempts (whether successful orunsuccessful) and that the information gained and skillslearned are shared. This volume (and the conference onwhich it was based) is a contribution to the vital process ofsharing knowledge to combat the threat of invasive alienspecies.

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Our aim in organising the 2001 ISSG Conference on Eradi-cation of Invasive Species and editing its proceedings intoa peer-reviewed volume was to bring together conserva-tion practitioners and scientists who are at the forefront ofthe battle against alien invasive species. This volume isintended to share their insight and practical experience witha wider audience. We thank all of the participants at the

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conference, especially those who have contributed papersto this volume. We also thank all those who peer-reviewedpapers and assisted in other ways with its production. Spe-cial thanks are due to Carola Warner, secretary to the IUCNInvasive Species Specialist Group, who helped us through-out with the task of compiling this book

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Atkinson, I. A. E. 1989. Introduced animals andextinctions. In Western, D. and Pearl, M. (eds.). Con-servation for the twenty-first century, pp. 54-69. Ox-ford, New York.

Bomford, M. and O’Brien, P. 1995. Eradication or controlfor vertebrate pests. Wildlife Society Bulletin 23: 249-255.

Chapin, F. S.; Zavaleta, E. S.; Viner, V. T.; Naylor, R. L.;Vitousek, P. M.; Sala, O. E.; Reynolds, H. L.; Hooper,D. U.; Mack, M.; Diaz, S. E.; Hobbie, S. E. and Lavorel,S. 2000. Consequences of changing biodiversity. Na-ture 405: 234-242.

Cowan, P. E. 1992. The eradication of introduced Aus-tralian brushtail possums, Trichosurus vulpecula, fromKapiti Island, a New Zealand nature reserve. Biologi-cal Conservation 61: 217-226.

Genovesi, P. and Bertolino S. 2001. Human dimension as-pects in invasive alien species issues: the case of thefailure of the grey squirrel eradication project in Italy.In: McNeely, J. (ed.). The great reshuffling: human di-mensions of invasive alien species, pp. 113-119. IUCN,Gland, Switzerland.

IUCN 2000. Guidelines for the prevention of biodiversityloss due to biological invasion. IUCN – The WorldConservation Union, Gland, Switzerland.

Mack, R. N.; Simberloff, D.; Lonsdale, W. M.; Evans. H.;Clout, M. and Bazzaz, F. A. 2000. Biotic invasions:causes, epidemiology, global consequences and con-trol. Ecological Applications 10: 689-710.

Veitch, C. R. 1995. Habitat repair: a necessary prerequi-site to translocation of threatened birds. In M. Serena,(ed.). Reintroduction biology of Australian and NewZealand fauna, pp. 97-104. Surrey Beatty & Sons,Chipping Norton, Australia.

Veltman, C. 2000. Do native wildlife benefit from possumcontrol? In T. Montague (ed.). The brushtail possum:biology impact and management of an introduced mar-supial, pp. 241-250. Manaaki Whenua Press, Lincoln,New Zealand.

Vitousek, P. M.; D’Antonio, C. M.; Loope, L. L.;Rejmanek, M. and Westbrooks, R. 1997. Introducedspecies: a significant component of human-caused glo-bal change. New Zealand Journal of Ecology 21: 1-16

Zaveleta, E. S.; Hobbs, R. H. and Mooney, H. A. 2001:Viewing invasive species removal in a whole-organismcontext. Trends in Ecology and Evolution 16: 454-459.

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D. SimberloffDepartment of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 U.S.A.

Abstract Eradication of invasive non-indigenous species is often viewed as an impossible goal and an approachhistorically typified by high-profile failures. However, there have been a surprising number of successful eradicationsof animals, plants, and even microorganisms. Although the majority of successes have concerned geographically-circumscribed invasions (e.g., on small islands), others have rid substantial continental areas of invaders (e.g., Anoph-eles gambiae from north-eastern Brazil, or smallpox from the entire Earth). Successful eradications share three fea-tures: (1) sufficient economic resources must exist for the project to be completed, (2) clear lines of authority must exist;someone must be in charge and must be able to compel cooperation, and (3) the biology of the target organism must beadequately researched and appropriate. For many but not all eradication attempts, probability of rapid re-invasion mustbe low for success to ensue. Further, even when the above criteria are met, an eradication attempt, even if successful,can lead to unforeseen problems, such as mesopredator release or a proliferation of non-indigenous weeds at the ex-pense of native plants. Finally, not only can attempted eradication of widely distributed invaders be costly, but it cangenerate non-target impacts (e.g., on human health or species of conservation concern), the importance of which will beweighed differently by different stakeholders. Thus, successful eradication may be as much a function of political skilland public education as of technology. When eradication is feasible, a benefit-cost analysis may help indicate when itis the best management strategy. To date, eradication has been a rather idiosyncratic matter, often resting on the driveand ingenuity of one person or a few people. This has partly resulted from lack of public interest in invasions. Otherdevelopments in management of invasions should increase the appeal of eradication attempts. The evolution of morecomprehensive monitoring and reporting systems, as well as more rapid response procedures, should lead to the morefrequent eradication of invasions before they become metastatic. However, even invasions that escape initial elimina-tion and spread widely may be susceptible to eradication. Many invasions that would, a priori, appear suitable by theabove criteria for eradication have not been attacked because no one has mustered the enthusiasm to try it or generatedthe political support to provide the necessary resources and framework. Moreover, we do not know the geographiclimits of current technologies. For example, just how great an investment would be required to rid a large island orsubstantial continental region of a pestiferous mammal? As with many other aspects of the invasion problem, eradica-tion may largely be a victim of an unwarranted fatalism that could generate the very outcome that is most feared – infact, we are not doomed to the biotic homogenisation of the Earth, but we will surely lose this war if we do not aim high.

Keywords defeatism; invasion economics; re-invasion; restoration; side effects.

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As biologists and the public worldwide increasingly rec-ognise the damage caused by invasive non-indigenous spe-cies (Mooney 1999), they usually assume that maintenancemanagement is the appropriate response. “Maintenancemanagement” means controlling an invader at a densitylow enough that we can tolerate the damage it causes.Maintenance options typically include mechanical, chemi-cal, and biological control, plus ecosystem management(Simberloff 2002). Although politicians occasionally callfor eradication of a new invader, the total removal of everysingle individual remains a controversial goal (e.g., Myerset al. 1998), and much of the scientific community viewsit as a bad idea (e.g., Dahlsten 1986) for three reasons: itis seen as unlikely to succeed, it may be costly, and it mayimpose substantial collateral damage. Some famous failederadications exemplify these problems. Probably the mostnotorious was the 14-year eradication project for the im-ported fire ant (Solenopsis invicta) in the southeasternUnited States (Davidson and Stone 1989), a legendary fi-

asco in terms of collateral damage (including to humans)and expense (over USD200 million) termed “the Vietnamof entomology” by E. O. Wilson (Brody 1975). The biol-ogy of the ant rendered successful elimination over verylarge areas impractical. This campaign probably wors-ened the fire ant invasion by causing greater mortality forits natural enemies than for the fire ant itself.

However, many invaders have been successfully eradicated(Myers et al. 2000; Simberloff 2001). To my knowledge,the earliest insect eradication was the elimination of thetse-tse fly (Glossina spp.) from the 126 km2 island ofPrincipe in the Gulf of Guinea (Lapeyssonie 1988). Theflies were introduced in cargo from Africa in 1825, andsleeping sickness was noted beginning in 1859, ultimatelyreducing the human population ten fold. A four-personteam completely eradicated the fly (and the disease) be-tween 1911 and 1914. In 1956, a tse-tse fly was againnoticed on Principe, and a large scientific team was imme-diately dispatched to the island, where they captured 66,894flies in two months. With the aid of traps, insecticides,

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extensive brush-clearing, and massive hunting to reducepopulations of pigs and wild dogs, the fly was again eradi-cated at a cost of £7500 and has not been seen since.Principe is an island (though not a tiny one), and manysuccessful eradications have occurred on islands. Theserange from small ones, such as the elimination of the screw-worm fly (Cochliomyia hominivorax) from Curaçao(Baumhover et al. 1955), Asian citrus blackfly(Aleurocanthus woglumi) from Key West (Hoelmer andGrace 1989), Oriental fruit fly (Dacus dorsalis) from Rotaand Guam (Steiner et al. 1955, 1965, 1970), and Pacificrats (Rattus exulans) from Tiritiri Matangi (Veitch 2002),to very large ones, such as nutria (Myocaster coypus) fromGreat Britain (Gosling 1989), yellow fever from Cuba(Fenner et al. 1988), and the melon fly (Bactroceracucurbitae) from the entire Ryukyu Archipelago, includ-ing Okinawa (Iwahashi 1996; Kuba et al. 1996).

Though many of the most striking recent eradications haveremoved various mammals from islands (e.g., Veitch andBell 1990; Chapuis and Barnaud 1995; Day and Daltry1996a, 1996b; Pascal 1996; Day et al. 1998; Pascal et al.1998; Varnham et al. 1998; Bell 1999; Donlan et al. 1999),successful eradication is not just an island phenomenon.The most widespread eradication eliminated smallpox fromthe face of the Earth (Fenner et al. 1988). One of the mostimpressive continental eradications was that of the Afri-can mosquito (Anopheles gambiae), a vector of malaria,from 31,000 km2 of north-eastern Brazil (Soper and Wilson1943; Davis and Garcia 1989). Other eradications fromlarge parts of continents include the screw-worm (first fromFlorida, then from the southeastern United States, then fromMexico, and most recently from several Central Ameri-can nations (Reichard et al. 1992; Galvin and Wyss 1996)),the cattle tick (Boophilus annulatus) from over a millionkm2 of the United States (Klassen 1989), and bovine con-tagious pleuropneumonia from the United States (Fenneret al. 1988). For the cattle tick example, there is occa-sional re-invasion (see below). Eradication from smallercontinental areas is fairly common, such as that of the gi-ant African snail (Achatina fulica) from a region of southFlorida (Mead 1979) and part of Queensland, Australia(Colman 1978), the medfly (Ceratitis capitata) from 20Florida counties (references in Simberloff 1997a), yellowfever from Panama (Fenner et al. 1988), karoo thorn (Aca-cia karoo) from Western Australia and Victoria, andTaurian thistle (Onopordum tauricum) from Victoria(Weiss 1999; R. Groves, pers. comm. 2000).

Of course, besides famous failures such as the fire ant cam-paign, there are many other attempted eradications thathave not resulted in the complete elimination of an invader;surely there are more such cases than total successes. Ihave not attempted a tally, because the literature is tooscattered and grey, and because colloquial use of the term“eradication” makes it difficult to assess exactly what is afailure (Simberloff 1997a, 2001). Often public figures(e.g., Chiles 1996) and even scientists (e.g., Langland andSutton 1992) use “eradication” to mean partial removaland substantial control. In these instances total eradica-tion was never even attempted. Should such a campaign

be viewed as a failure? This assessment seems undulyharsh if the same method used in the eradication campaignwould have been used for maintenance management, andif substantial control results even though elimination is notcomplete, as in the attempt to eradicate Spartina spp. fromNew Zealand (Nicholls 1998).

In the remainder of this paper I attempt to parse the suc-cesses and failures to seek guidance as to when eradica-tion is feasible. Do common features characterise suc-cessful campaigns? Do similar problems plague manyfailures? At the outset, I emphasise that I am not address-ing whether society as a whole wants a particular invaderremoved or even controlled. Often one faction wants toeliminate a species that others see as a boon – note thebattle in Australia over Echium plantagineum, termedPaterson’s curse by ranchers and Salvation Jane by apia-rists (Cullen and Delfosse 1985). Rather, assuming thatsociety does want to control a particular species, I will askwhat is the best means.

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Eradication on a small scale may not require enormousresources; the enthusiasm and hard work of a single per-son or a small, non-governmental organisation may evensuffice. For example, a dedicated group of scientists (theIsland Conservation & Ecology Group) has succeeded inremoving various combinations of feral cats (Felis catus),Norway and black rats (Rattus norvegicus and R. rattus),house mice (Mus musculus), rabbits (Oryctolagus cunicu-lus), goats (Capra hircus), sheep (Ovis aries), and burros(Equus asinus) from nine islands in north-west Mexico(Donlan et al. 1999). However, for large areas, costs areoften huge. For 50 infestations of 16 plant pests of Cali-fornia, Rejmánek et al. (2000) found that log (cost) in-creased linearly and rapidly with log (infested area). Suc-cessful large regional eradications have been supportedby significant government resources and/or private invest-ment. The Brazilian eradication of Anopheles gambiae wasfunded by the Rockefeller Foundation and the Braziliangovernment (Davis and Garcia 1989), the screw-wormeradication in the United States and Mexico cost UnitedStates taxpayers USD750 million (Reichard et al. 1992),while the reduction of the African root parasite witchweed(Striga asiatica) in the Carolinas from 162,000 ha in the1950s to c. 2800 ha now entailed the massive support andcooperation of the United States government and the stategovernments of North and South Carolina (Westbrooks1993). Of course, huge budgets do not ensure success –witness the fire ant eradication disaster. However, for eradi-cation over substantial areas, big budgets are generally aprerequisite (Myers et al. 2000; Simberloff 2001b).

The fact that expense increases rapidly as area of an inva-sion increases leads to the dictum that it is best to eradi-cate early (e.g., Simberloff 1997a; Weiss 1999; Myers etal. 2000). Although some longstanding, widespread inva-sions have been eradicated, likelihood of success is obvi-ously improved and cost minimised if an invasion is nipped

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in the bud. This fact argues for effective early warningand rapid response machinery (Simberloff 1997b; Weiss1999), a subject beyond the scope of this paper. Two casesexemplify the benefits of acting very quickly when eradi-cation is the goal. The Caribbean black-striped mussel(Mytilopsis sallei), was discovered in 1999 in Cullen Bay(600 megalitres, 12.5 ha), Darwin Harbour, within sixmonths of its arrival and before it had spread further inAustralia. Within nine days the bay had been quarantinedand treated with 160,000 l of liquid bleach and 6000 met-ric tonnes of CuSO

4. All living organisms were believed

killed, and the mussel population was eradicated (Myerset al. 2000; Bax et al. 2002). The tropical alga Caulerpataxifolia could almost certainly have been eliminated inthe Mediterranean soon after its discovery, when it wasrestricted to a few square metres in front of the Oceano-graphic Museum of Monaco, but the effort was delayedfor years and the alga now infests several thousand hec-tares of the coasts of Spain, France, Monaco, Italy, andCroatia (Meinesz 2001). By contrast, an effort to eradi-cate a small infestation of the same alga near San Diegowithin a year of its discovery seems promising (Meinesz2001). An attempt to combat a much larger infestationnear Los Angeles using similar methods is more problem-atic.

Some expenses of eradication campaigns can be substan-tial and not obvious at the outset (Myers et al. 1998). Kill-ing the first 99% of a target population can cost less thaneliminating the last 1%. This fact can become a problemwith governmental funding authorities, who may be in-clined to lessen support for a programme once the prob-lem subsides, rather than see it through to completion(Schardt 1997; cf. Mack and Lonsdale 2002). Costs ofmonitoring may increase when pest densities are very low,yet intensive monitoring is the only effective way to deter-mine when to end an eradication campaign. Dependingon the target species and the means employed to removeit, an expensive public relations campaign may be neededto ensure public support, and lawsuits may have to be con-tested (Myers et al. 1998). For instance, for just part of aCalifornia medfly eradication project, 14,000 claims werefiled for damage to car paint, and the state of Californiapaid USD3.7 million (Getz 1989).

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It is always difficult to induce large groups of people withdiverse interests to support a programme when the ben-efits seem unequally distributed, and eradication frequentlyfalls in this category. Because eradication can, by its na-ture, be subverted by one or a few individuals, some gov-ernment agency or interagency entity must have the abil-ity to compel cooperation (Myers et al. 2000; Simberloff2001b). In nations or regions with strong distrust of gov-ernment, such authority will automatically generate oppo-sition (cf. Perkins 1989). Specific concerns about the eradi-cation techniques may be so vehement that only a stronggovernmental authority can enact the programme. Aerialspraying of malathion to eradicate medflies fostered wide-

spread complaints about discomfort or threats to humanhealth in California (Penrose 1996) and Florida (Anon.1997). Killing large vertebrates by trapping, hunting, orpoisoning often generates vocal opposition – witness theoutcry over snaring feral pigs (Sus scrofa) in the Hawaiianislands (Van Driesche and Van Driesche 2000), trappingnutria in Great Britain (Gosling 1989), and shooting monkparakeets (Myiopsitta monachus) in the United States(Simberloff 1997a).

When human health is at stake, as in the tse-tse eradica-tion on Principe or in Nigeria (Oladunmade et al. 1986) orthe malaria mosquito eradication in Brazil, even heavy-handed government control is less likely to generate op-position. When an eradication campaign directly ben-efits agriculture, and the costs and possible side-effectsare borne by the entire public as in spraying malathion tokill medflies, perceived inequities are more likely to gen-erate conflict (Simberloff 2001b). Most eradications at-tempted for conservation purposes have occurred on smallislands, often with little or no human population, and op-position has usually been minimal. Until conservationachieves a higher value in the eyes of the entire public, Ipredict that attempts to eradicate ecological pests over wideareas will engender hostility because of economic or emo-tional costs or side-effects. On a small scale, the localattempts to eradicate Asian long-horned beetles(Anoplophora glabripennis) by felling urban trees in Chi-cago and New York, and to eradicate citrus canker inFlorida by destroying citrus trees, gave a foretaste of com-plaints that will arise if this campaign must be greatly ex-tended (e.g., Stout 1996; Toy 1999; Sharp 2000); of course,the ultimate purpose in these instances is silvicultural oragricultural more than ecological. I know of no large-scale eradication projects conducted solely for conserva-tion purposes, though some carried out primarily for agri-cultural or silvicultural reasons are perceived as havingconservation benefits (e.g., that of the gypsy moth(Lymantria dispar)(Myers et al. 2000)).

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A sufficiently-determined effort can probably eradicate al-most any species in a small enough area, but certain bio-logical features can make a target less tractable. Wheneradication must be conducted over a large region, the bi-ology of the target species may be particularly crucial andthe scientific knowledge must be profound (Fenner et al.1988; Myers et al. 2000; Simberloff 2001b). Some traitsconducive to successful eradication are obvious – for ex-ample, large mammals are far easier to find than smallinsects, while plants with a soil seed bank are more diffi-cult to eliminate than those without this feature (Simberloff2001b). However, key biological traits often require sub-stantial research, usually in the vein of natural history.Biological features figure large in successful eradications:smallpox has no non-human reservoir or long-term carri-ers (Fenner et al. 1988); the giant African snail does notself-fertilise (Mead 1979); Anopheles gambiae in Brazilwas found almost exclusively near buildings (Hoelmer and

3

Grace 1989); while citrus canker (caused by Xanthomonasaxonopodis pathovar citri), eradicated in the south-east-ern United States in the early 20th century, had a very re-stricted host range and required movement of infected hostsby humans to spread (Merrill 1989). A recent successfuleradication resting on carefully-determined biology of apest and host was that of an introduced sabellid polychaete(Terebrasabella heterouncinata), parasitising abalone(Haliotis spp.) and other molluscs in Cayucos, California(Culver and Kuris 2000). The worms are specific to gas-tropod shells, especially large individuals of two commonspecies, while the gastropod hosts have pelagic larvae,ensuring their rapid re-colonisation. The removal of 1.6million highly susceptible hosts reduced the threshold hostdensity below a point at which the worm could persist.

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Is the effort to eradicate an invader worth it if rapid re-invasion is likely? One reason so many eradication at-tempts have been on islands is that their isolation suggestsimmunity from rapid re-invasion. In many circumstances,even a successful eradication campaign can be a wastedeffort because of re-invasion. In Washington state, an in-tensive campaign rid Long Lake (130 ha) of Eurasian wa-ter milfoil (Myriophyllum spicatum) (Thurston CountyDepartment of Water and Waste Management 1995).However, a public boat ramp permitted quick re-invasion,and the county switched to a programme of maintenancemanagement by hand-pulling (M. Swartout, pers. comm.1999). Other times, the probability of deliberate subver-sion of an eradication (Perkins 1989) is so high that theattempt may be futile. The reappearance of northern pike(Esox lucius) in Lake Davis, California, after its appar-ently successful eradication (Anon. 1999) probably re-sulted from sabotage (P. Moyle, pers. comm. 1999). Theease with which a single individual can subvert an eradi-cation of some species (e.g., Davis 1990) may be an argu-ment against the attempt when the goal is controversial.

In general, whether the probability of re-invasion shouldforestall an eradication campaign rests on a full assess-ment of the likely costs and benefits. There may be rea-sons to attempt eradication even if re-invasion is prob-able. For instance, sometimes the benefit of an eradica-tion campaign may be a biologically artificial one, in thattrade regulations may prohibit importation of some goodunless its region of origin is certified as free of a pest. Insuch instances, the economic benefits may be so great thatcertain re-invasion would not argue against eradication at-tempts. This is the reason government officials repeat-edly mount expensive eradication campaigns against themedfly in California and gypsy moth in parts of the UnitedStates and Canada in spite of a high probability of rapidre-infestation (Myers et al. 2000). This is not to say thatthe ecological and/or economic benefits of either of thesecampaigns might not suffice to justify them even in theabsence of trade regulations. The point I am making isthat low-level maintenance management, as opposed toeradication, is not an option because of trade regulations,

even if maintenance management would achieve greaterreal control and/or cost less.

Independent of trade regulations, an eradication campaigncan have sufficient economic, ecological, health, or evensymbolic benefits to warrant the cost even if quick re-in-vasion is certain. In the successful eradication of the cat-tle tick from the United States, described above, re-infes-tation into the lower Rio Grande River region of Texascontinually occurs through movement of infected animalsfrom Mexico; leading to frequent small control operations(Klassen 1989). No one doubts the value of this pro-gramme. The Alberta rat control programme (Bourne2000; Holubitsky 2000) is an inspirational eradicationexample despite frequent re-invasion. Norway rats (Rat-tus norvegicus) were first discovered on the eastern bor-der of Alberta in 1950. Because rats destroy crops, everylandowner and municipality in Alberta is mandated to de-stroy them, but the provincial government now pays allcosts. The bulk of the activity is conducted by pest con-trol inspectors hired and supervised by municipalities alongthe Alberta-Saskatchewan border. Every premise withina 29 x 600 km border zone is inspected at least annually,and control is effected primarily by eliminating foodsources, extensive use of anticoagulant baits, and huntingby a team of seven provincial rat patrol officers. The costis about CA$350,000 annually. Of course, re-invasion iscontinual, and every year between 36 and 216 infestationsare discovered and destroyed. However, Alberta is so rat-free that discovery of a single rat in Edmonton or Calgaryreceives full media coverage. Aside from the benefit toagriculture of eliminating crop loss to rats, the programmehas engaged the population of the entire province and sen-sitised them to the potential dangers of failing to dealpromptly and comprehensively with invading species.

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Simply removing an invader does not constitute restora-tion (Towns et al. 1997). An ecological restoration schemefounded on eradication may be defeated by re-invasion orother problems (Simberloff 2001). Key species may beextinct and no acceptable functional equivalents available.Restoration efforts are sometimes mysteriously unsuccess-ful. For instance, after eradication of predators, re-intro-duction of stitchbirds (Notiomystis cincta) to New Zea-land islands has failed to produce self-sustainingpopulations, and reasons are not apparent (Towns et al.1997). Our knowledge of community structure and func-tion is inadequate to predict with assurance the impacts ofremoving a prominent member of an ecological commu-nity. Thus, unforeseen impacts of eradication abound (ref-erences in Towns et al. 1997). Mouse densities increasedgreatly following eradication of Norway rats from MokoiaIsland. Even control of top predator densities at levels farabove eradication can lead to increases in densities of in-termediate predators (“mesopredator release”; Terborghet al. 1999) with various further effects throughout thecommunity. Elimination of a predator can also lead toincreased herbivore populations and damage; eradication

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of Pacific rats (Rattus exulans) from Motuopao Island toprotect a native snail resulted in detrimental increases in anon-indigenous snail instead. Removal of an introducedherbivore can lead to proliferation of non-indigenous weedsrather than restoration of the native plant community.Eradication of rabbits from Motunau Island led to increasesof introduced boxthorn (Lycium ferocissimum), while re-moval of grazing livestock from Santa Cruz Island (Cali-fornia) caused dramatic increases in fennel (Foeniculumvulgare) and other introduced plants (Dash and Gliessman1994). Such changes in vegetation structure followingelimination of an herbivore can, in turn, affect animalpopulations. For example, removal of cattle in bothNebraskan prairie (Ballinger and Watts 1995) and ManaIsland, New Zealand (Newman 1994) has decreased na-tive lizard populations by modifying vegetation.

Some impacts of eradication described in the previousparagraph might have been predicted, but others are soidiosyncratic that even a substantial scientific researchproject might not have suggested them. Thus, eradicationis often a large, uncontrolled experiment, and we shouldexpect unforeseen outcomes (Simberloff 2001b).

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So far, I have addressed primarily the feasibility of eradi-cating a pest, with some attention to benefits that mightaccrue even if an eradication attempt is unsuccessful, aswell as to unforeseen problems. I have thus avoided thekey question of whether eradication is an appropriate ap-proach even if it is feasible. Of course the prospect ofpermanent removal of an invader from a region, and thusthe elimination of annual management costs as well as thedanger of some delayed impact, must be very seductive.However, given the great costs that may be associated withsuccessful eradication, especially over a substantial area,society cannot undertake to eradicate every pestiferousinvader for which there is a high probability of eradica-tion success. Prioritisation of invaders for managementaction is a general problem, and eradication decisions arejust a part of that problem. Which invaders cause, or arelikely to cause, the most damage, and under what circum-stances is eradication the best of available managementoptions? Typically such decisions are based on benefit-cost analyses (Arrow et al. 1996), but benefit-cost analy-ses of many natural resource issues, particularly those re-lated to conservation, are problematic because there is oftenno market, as there is for an agricultural commodity(LeVeen 1989; Simberloff 1992). In the new field of in-vasion economics, benefit-cost analyses are especiallyproblematic and have rarely if ever been adequately per-formed (Perrings et al. 2000). One problem is the greatdifficulty in predicting the trajectory of invasions, whileanother is the difficulty of predicting the impacts of vari-ous kinds of control measures. Surely benefit-cost analy-ses will have extremely wide confidence limits for manyyears to come.

Nevertheless, in certain circumstances, it seems that aneradication attempt would surely be justified by a com-prehensive benefit-cost analysis. For smallpox (Fenner etal. 1988), the entire annual national and international costof the eradication from the inception of a full-fledged cam-paign in 1967 to its success in 1979 was only USD23 mil-lion, while the annual cost of the disease (not countingcontrol efforts) during this period to underdeveloped na-tions alone was at least USD1.07 billion, and worldwidewas estimated as USD1.35 billion. The annual cost ofcontrol efforts before the eradication campaign just in theUnited States was USD150.2 million. Even if the cam-paign had not succeeded, so long as it had even a moder-ate probability of success, it would seem to have been anappropriate investment.

Just a rapid glance at the annual current management costs(not including losses and damages) estimated for someinvaders in the United States (Pimentel et al. 2000) sug-gests that even an expensive eradication campaign mightbe appropriate, so long as the prospects of success wereeven moderate and the attempt would not substantiallyinterfere with, or foreclose, other effective managementtechniques. Every year, the United States spends USD45million on purple loosestrife (Lythrum salicaria) control,USD3-6 million on management of Melaleucaquinquenervia, USD4.6 million to manage the browntreesnake (Boiga irregularis) on Guam, and USD100 mil-lion to deal with Dutch elm disease (Ophiostoma ulmi).However, the real prospects of successful eradication ofany of these species would have to be assessed based ondetailed knowledge of its biology, and alternative meth-ods (e.g., the recently released biological control agentsfor the first two species) may end up producing adequatecontrol at far lower than current expenditures. My pointin listing these examples is that each one entails an enor-mous annual expenditure, and I wonder if the possibilityhas been considered that total, long-lasting eradicationcould be achieved for, say, 10 or 20 times the current an-nual control cost, plus future costs of prevention. Do re-source managers typically think this big?

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There are some spectacular large-scale eradication suc-cesses. And there is a growing string of smaller successes.Further, a wide array of techniques has been successfullydeployed – sterile insect release, male annihilation, traps,pathogens, vaccination, chemical sprays and baits, hunt-ing, dogs, Judas goats, host removal, fire, and many othergory procedures. Nevertheless, eradication is almost astepchild of management of invasives, often not consid-ered as a possible solution even when the specifics of asituation might augur well for success. I see two mainreasons for this disconnect:

� First, the literature on eradication is scattered and oftenvery grey. Eradication of mammals is published in dif-ferent outlets from insect eradication, and plant eradi-cation histories, when published at all, are found in yet

5

other sources. This conference is the first internationalconference spanning the entire field of eradication, andthe number and high quality of presentations shows thatthe organisers have struck a very responsive chord. Ipredict that the published proceedings will go a longway towards both unifying the field and attracting theattention of policy makers, managers, and invasion bi-ologists. In addition, leaders of eradication projectsmust recognise high-quality, international publicationas a normal part of the job. If we want eradication tobecome a real option in managing invasive species, wehave to publicise the methods and results better.

� Second, the entire problem of introduced species seemsso overwhelming that it has induced a sort of fatalism –the forces arrayed against us, particularly the growingmovement of cargo and people in the free-trade era,seem so overwhelming that some authors see us doomedto an eventual global homogenisation (e.g., Quammen1998). Eradication, both because of publicised fail-ures and because it is, in a sense, the management ap-proach that aims the highest, falls victim to this fatal-ism even more acutely than other methods. But surelythis sense of unavoidable doom is unwarranted. Weknow that eradication can work because it has. It hasworked despite the relatively poor lines of communica-tion I have outlined above and despite what would of-ten seem to be the awesome biological powers of thetarget invader. New Zealanders have even developedan export industry of advice on, and application of, is-land mammal eradication techniques. What we do notknow are the limits of most of these technologies. Justhow large an island could be cleared of rodents by thetechniques developed in New Zealand and northwest-ern Mexico? If the political will and economic supportcould be mustered, could nutria be completely eradi-cated in North America? Rabbits in Australia? Whatabout invasive plants – under what circumstances couldthe witchweed approach be replicated? If smallpox andcitrus canker can be eradicated, are insects on conti-nents really out of the question?

I do not know the answers to these questions, but the in-spirational stories from the literature and this conferencesuggest that we should not sell ourselves short. It is worth-while to reflect on the defeatism expressed by the distin-guished scientist René Dubos (1965) as he reflected onhuman disease eradication on the eve of the successfulcampaign to eliminate smallpox: “…it is easy to write lawsfor compulsory vaccination against smallpox, but in mostparts of the world people would rather buy the vaccina-tion certificate than take the vaccine; and they shall al-ways find physicians willing to satisfy their request for asmall fee. For this reason, and many others, eradicationprograms will eventually become a curiosity item on li-brary shelves, just as have all social utopias.” One thing iscertain – we will surely lose the war against invasive non-indigenous species if we consider eradication an impossi-ble fantasy and not an attainable reality.

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I thank the conference organisers for the opportunity toaddress this exciting conference, and J. Bourne, R. Groves,M. Lonsdale, P. Moyle, M. Rejmánek, J. Spence, and M.Swartout for information on particular eradication cam-paigns. T. Campbell, R. Mack, M. Núñez, M. Tebo, andD. Towns commented on a draft of the manuscript.

� # � �� !

Anonymous. 1997. Medfly flybys cut back following com-plaints. Tallahassee Democrat, July 9, p. 10c.

Anonymous. 1999. Pike reappear, and a California city ison guard. New York Times, June 21, p. 12.

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Colman, P. H. 1978. An invading giant. Wildlife in Aus-tralia 15(2): 46-47.

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Cullen, J. M. and Delfosse, E. S. 1985. Echiumplantagineum: Catalyst for conflict and change in Aus-tralia. In Delfosse, E. S. (ed.). Proceedings of the VIInternational Symposium on Biological Control ofWeeds, pp. 249-292. Vancouver, Agriculture Canada.

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Davis, J. R. and Garcia, R. 1989. Malaria mosquito in Bra-zil. In Dahlsten, D.L. and Garcia, R. (eds.). Eradica-tion of Exotic Pests, pp. 274-283. New Haven, Con-necticut, Yale University Press.

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D. A. Algar, A. A. Burbidge, and G. J. AngusDepartment of Conservation and Land Management, Science Division, P. O. Box 51, Wanneroo,

WA 6946, Australia. E-mail: davea@calm.wa.gov.au.

������� Feral cats (Felis catus) and black rats (Rattus rattus) became established on the Montebello Islands, anarchipelago of about 100 islands, islets and rocks off the Pilbara coast of Western Australia, during the late 19th century.They were probably introduced from pearling vessels. The largest island in the group is Hermite at 1020 ha. Threespecies of native mammals and two of birds became extinct well before the British used the islands for testing nuclearweapons in the 1950s. Montebello Renewal (part of the ‘Western Shield’ fauna recovery programme) aims to eradicateferal animals from, and reintroduce and introduce threatened animals to, the Montebellos. Rats occurred on almostevery island and islet when eradication was attempted in 1996. In 1999 small numbers of rats were detected on Hermiteand two adjacent islands and work is under way to eliminate them. Feral cats occurred on several islands at varioustimes, but by 1995 were naturally restricted to Hermite. Feral cat eradication took place in 1999 and comprised twostages – aerial baiting and trapping. Aerial baiting utilised recently developed kangaroo meat sausage baits with flavourenhancers and the toxin 1080. About 1100 baits were dropped by hand from a helicopter. Hermite Island has two mainsoil types – sand and limestone. Aerial baiting primarily targeted sandy soils. Four cats, all females, remained afterbaiting. These were trapped using Victor ‘softcatch’® traps set either in association with phonic and odour lures or setin narrow runways. Eradication was achieved over a six-week period. Searches for evidence of cat activity in 2000confirmed that cats had been eradicated.

������� cat eradication; islands; cat bait; cat trapping.

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The importance of islands to the conservation of Austral-ian mammal species has been well documented (Burbidgeand McKenzie 1989; Abbott and Burbidge 1995; Burbidgeet al. 1997). One of the key factors in the historic impor-tance of islands has been that most have remained free ofintroduced predators. Burbidge (1999) highlighted thecurrent and future importance of islands to nature conser-vation and stated that ‘Australian nature conservation agen-cies need to pay more attention to the eradication of ex-otic animals from islands’.

Feral cats (Felis catus) pose a serious threat to populationsof small to medium-sized native vertebrates. Anecdotalevidence has indicated that predation by feral cats, eitheracting singly or in concert with other factors, has resultedin the local extinction of a number of species on islandsand mainland Australia. Burbidge and Manly (2002) ana-lysed the relationship between disturbances and nativemammal extinctions on Australian islands and implicatedferal cats in the extinction of these species on arid islands.They concluded that high estimated extinction probabili-ties are associated with ground dwelling, herbivorous,‘critical weight range’ mammals of high body weight onislands of low rainfall, low to moderate presence ofrockpiles and the presence of cats, foxes and rats.

Predation by feral cats also affects the continued survivalof many native species that persist at low population lev-els (Dickman 1996; Smith and Quin 1996) and has pre-vented the successful re-introduction of species to parts oftheir former range (Gibson et al. 1994; Christensen and

Burrows 1995). Control of feral cats is recognised as animportant conservation issue in Australia today and as aresult, a national ‘Threat Abatement Plan for Predation byFeral Cats’ has been developed (Environment Australia1999). The Department of Conservation and Land Man-agement (CALM), through Project ‘Western Shield’, hasbeen working over the past few years to develop an effec-tive cat control strategy. Montebello Renewal (part of‘Western Shield’), which aims to eradicate rats and catsand to reintroduce locally extinct species, provided an op-portunity to assess the effectiveness of these techniques toeradicate cats from an island.

The Montebello Islands comprise a group of over 100 is-lands, islets and rocks off the Pilbara coast of WesternAustralia. The archipelago has a tropical, arid climate. Thenearest weather station is on Barrow Island, 30 km to thesouth, which has a median rainfall of 285 mm, and meandaily maximum and minimum temperatures of 30.3°C and21.4°C respectively.

Montague (1914) conducted the first detailed biologicalsurvey of the islands in 1912. He observed the presence ofcats and noted that they had probably established from ashipwreck 20 or so years before his visit. It seems morelikely, however, that cats were introduced from pearlingvessels that were active in the area from the 1860s.Montague attributed the recent extinction of the goldenbandicoot (Isoodon auratus) to predation by cats and pre-dicted that the spectacled hare-wallaby (Lagorchestesconspicillatus) would suffer the same fate. Later surveysby Sheard (1950) and Serventy and Marshall (1964) found

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that both species had become locally extinct on the islands,confirming Montague’s prediction.

The above surveys recorded cats on Hermite Island, at1020 ha the largest island in the group. However, cats werealso observed on Trimouille Island in 1970 (Burbidge1971) and tracks were recorded by K. D. Morris on Blue-bell Island in 1985 (Burbidge et al. 2000). Surveys be-tween 1994 and 1996 found that cats were then restrictedto Hermite Island, indicating that populations on the smallerislands had died out without human intervention (Burbidgeet al. 2000).

Montebello Renewal aims to eradicate feral cats and blackrats (Rattus rattus) from the Montebello Islands to allowthe successful re-introduction of native mammal speciesand also two species of locally extinct birds: spinifexbird(Eremiornis carteri) and the black-and-white fairy-wren(Malurus leucopterus leucopterus) (Burbidge 1997). Theabsence of cats and eradication of rats from TrimouilleIsland has allowed this island to be used for the introduc-tion of species threatened with extinction on mainlandAustralia. The mala (Lagorchestes hirsutus unnamed cen-tral Australian subspecies), which is ‘extinct in the wild’

and is subject to predation by feral cats, has been success-fully established on Trimouille Island (Burbidge et al.1999, 2000; Langford and Burbidge 2001). The djoongari(Shark Bay mouse, Pseudomys fieldi), also threatened byferal cat predation, was introduced to North West Islandin June 1999 and August and October 2000.

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The Montebello Islands are located between 20º21’ and20º32’ South and between 115º31’ and 115º36’ East, ap-proximately 100 km off the Western Australian coast. Thetotal area of the islands is approximately 2300 ha withHermite Island being the largest at 1020 ha. Hermite Is-land is a difficult location on which to conduct a cat eradi-cation campaign because of its isolation, rugged terrainand absence of vehicle access. The shape of the island iselongated and highly convoluted, with a number of sandybeaches, areas of mangroves, cliffs and limestone ridgesand peninsulas (Fig. 1). Its interior is low, undulating andis vegetated with a dense mat of spinifex (Triodia sp.) withoccasional Acacia coriacea thickets on deep sand. Accesswas via small boat along Stephenson Channel and then onfoot, carrying the traps and trapping equipment.

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The programme to eradicate feral cats on Hermite Islandinvolved aerial baiting to remove the majority of the cats,followed by intensive trapping, if warranted, to removethe remaining individuals. A reconnaissance of HermiteIsland was conducted prior to the baiting programme toassess cat abundance. Searches for evidence of fresh catactivity were conducted around most mangrove stands andsandy areas on the island. These were examined daily overa five day period. The location of fresh cat activity onswept areas, its extent and the distances between sites sug-gested that at least 20 cats were present prior to baiting.

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CALM researchers have recently completed developmentof a bait to control feral cats. The bait is similar to a chipo-lata sausage. It is 20 g in weight and contains a number offlavour enhancers that are highly attractive to feral cats(Patent No. AU 13682/01). The baits were manufacturedat the Department’s Bait Factory and airfreighted to theisland. At the island the baits (National Registration Au-thority experimental baiting permit No. 1213) wereprepared for laying by thawing and then blanching (thatis, placing in boiling water for one minute). The toxin 1080(sodium monofluoroacetate) was injected into the baits ata rate of 3.0 mg/bait. A risk analysis concluded that thereare unlikely to be any significant effects on non-target spe-cies on the island. All baits were treated with an ant deter-rent compound (Coopex®) at a concentration of 12.5 g /lCoopex as per the manufacturer’s instructions. Ant