New Zealand Journal of Zoology ISSN: 0301-4223 (Print) 1175-8821 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzz20 From small Maria to massive Campbell: Forty years of rat eradications from New Zealand islands David R. Towns & Keith G. Broome To cite this article: David R. Towns & Keith G. Broome (2003) From small Maria to massive Campbell: Forty years of rat eradications from New Zealand islands, New Zealand Journal of Zoology, 30:4, 377-398, DOI: 10.1080/03014223.2003.9518348 To link to this article: https://doi.org/10.1080/03014223.2003.9518348 Published online: 30 Mar 2010. Submit your article to this journal Article views: 1990 Citing articles: 141 View citing articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tnzz20 New Zealand Journal of Zoology, 2003, Vol. 30: 377-398 377 0301–4223/03/3004-0377 $7.00/0 © The Royal Society of New Zealand 2003 From small Maria to massive Campbell: forty years of rat eradications from New Zealand islands DAVID R. TOWNS species such as large flightless invertebrates, lizards, School of Biological Sciences tuatara, forest birds, and some species of plants. The Victoria University of Wellington most ambitious campaigns have been on remote New Zealand subantarctic Campbell Island (11 300 ha) and warm and temperate Raoul Island (2938 ha), aimed to provide Science and Research Unit long-term benefits for endemic plant and animal Department of Conservation species including land and seabirds. Other islands that could benefit from rat removal are close inshore Private Bag 68 908, Newton and within the natural dispersal range of rats and Auckland, New Zealand* stoats (Mustela erminea). Priorities for future email: [email protected] development therefore include more effective KEITH G. BROOME methods for detecting rodent invasions, especially Northern Regional Office ship rats (Rattus rattus) and mice (Mus musculus), Department of Conservation broader community involvement in invasion P.O.Box 112 prevention, and improved understanding of Hamilton, New Zealand reinvasion risk management. Keywords kiore; Pacific rat; Rattus exulans; Abstract Over the last four decades the eradica- Norway rat; R. norvegicus; ship rat; R. rattus; tion of rats from islands around New Zealand has eradication; adaptive management; Breaksea Island, moved from accidental eradication following the Mercury Islands; Kapiti Island, Tuhua Island; exploratory use of baits for rat control to carefully rodenticide; brodifacoum; aerial spread; legal planned complex eradications of rats and cats (Felis constraints; Resource Management Act 1991; catus) on large islands. Introduced rodents have now invasion biology; benefits; costs; cultural issues been eradicated from more than 90 islands. Of these successful campaigns, those on Breaksea Island, the Mercury Islands, Kapiti Island, and Tuhua Island are used here as case studies because they represent INTRODUCTION milestones for techniques used or results achieved. In about 1962, ship rats invaded Big South Cape Successful methods used on islands range from bait Island off southern New Zealand. Subsequently, the stations and silos serviced on foot to aerial spread last populations of bush wren (Xenicus longipes) and by helicopters using satellite navigation systems. The short-tailed bat (Mystacina robusta) disappeared development of these methods has benefited from along with at least one species of large invertebrate adaptive management. By applying lessons learned (Atkinson 1989). This was not the first recorded from previous operations the size, complexity, and invasion of islands by rats in the New Zealand cost effectiveness of the campaigns has gradually archipelago (Atkinson 1973). However, it was one increased. The islands now permanently cleared of of the first to be documented, including an account introduced rodents are being used for restoration of of attempts made to save the species under threat island-seabird systems and recovery of threatened (Atkinson & Bell 1973; Atkinson 1989). Unfortunately, these failed for all but the South Island saddleback (Philesturnus c. carunculatus) *Address for correspondence. (Bell 1978). Given that such islands are storehouses Z03016; online publication date 16 October 2003 for much of New Zealand's biodiversity (Daugherty Received 24 April 2003; accepted 31 July 2003 et al. 1990), the progressive demise of unique 378 New Zealand Journal of Zoology, 2003, Vol. 30 remnants of the New Zealand flora and fauna to Polynesian colonisation in about 1200-1300 AD invading rodents then seemed inevitable. (Anderson 1991; McFadgen et al. 1994). Two Awareness of this potential ecological catastro- additional species of rat were introduced phe formed the background for a meeting held in subsequently by Europeans. Norway rats (Rattus 1976 organised by the Department of Lands and norvegicus) dispersed from ships during exploration Survey to discuss and collate information on control- of New Zealand from 1769, and ship rats spread ling the spread of rodents into reserves (Dingwall et throughout New Zealand after about 1860-1890 al. 1978). The participants came to the depressing (Atkinson 1973). The disappearance of kiore from conclusion that unless existing controls on island much of mainland North and South Island coincided landings were enforced, the spread of rodents would with the arrival of mice and ship rats (Atkinson 1973; continue unchecked. Put simply, if rats invaded an Taylor 1975). island, "the prospect of complete extermination…. by conventional control methods is considered remote" Distribution of rats and their effects on island (Wodzicki 1978). But in one of the great species breakthroughs of New Zealand conservation A review by Atkinson & Taylor (1992) concluded biology, even as these conclusions were published, that rats had reached at least 113 (33.5%) of the 337 those unlikely eradications were already being islands over 5 ha. Rats also occupied numerous achieved using methods and products available at islands of less than 5 ha (Taylor 1989). The current the time. pattern of rat distribution in New Zealand is Below, we outline how eradication of rats from influenced by several ecological and historical New Zealand islands has progressed over 40 years factors including interspecific competition, size and from unexpected eradications on small islands of less complexity of habitat, historical opportunity to than 5 ha to sophisticated and logistically demanding invade, and nowadays, history of rodent eradications. campaigns on islands of more than 11 000 ha. We Large islands (>1000 ha) may support more than one also outline the financial costs and biological rat species, plus mice, and other predators including benefits of selected campaigns, changes in legal stoats and cats (Atkinson & Taylor 1992). Of the rat constraints, and examine where future efforts may species on islands, kiore may coexist with mice and focus. at least one other species of rat. However, kiore For the purposes of this review we distinguish usually now survive only on the smaller and more between eradication and control. Eradication distant islands, perhaps due to a lack of contact with involves the complete removal of a species from a other rats (but see Roberts 1991). Regardless of rat location into which there is little chance of reinvasion species present, islands less than 1500 m from the by natural dispersal. Control is a reduction of the mainland are also accessible to stoats. The effects population size of a species, by sustained and of rats on island species are therefore sometimes constant effort (Parkes 1990). We also refer to complicated by other species of rodents or additional adaptive management, which is viewed here as the predators other than rats. use of new information to adjust a strategy or goal Kiore have frequently survived on islands as the in order to learn from experience (Lessard 1998 and only introduced predatory mammal. Therefore, references therein). For example, this approach has models of the effect of rodents without complicat- been applied successfully in New Zealand to ing effects of other pests are best constructed for management of kokako (Calleas cinerea) (Innes et New Zealand species using islands inhabited only by al. 1999) and to intensively managed mainland sites kiore (Atkinson & Towns 2001). Circumstantial (Saunders & Norton 2001). evidence of these effects has been based on between- Three species of rats now occupy the New island comparisons and investigation of the fossil Zealand archipelago. Their introduction was closely record. These methods have revealed localised associated with the arrival of people. The first to extinctions of large flightless invertebrates, arrive was the Pacific rat or kiore (Rattus exulans), especially the darkling beetle (Mimopeus elongates) possibly with visiting voyagers from the Pacific (Watt 1986), as well as large nocturnal skinks such about 2000 years ago (Holdaway 1996). If this as Cyclodina alani (Whitaker 1978). The decline to proposal is correct, kiore were probably on the extinction of at least six species of passerine birds mainland of New Zealand for a considerable period also coincided with the arrival of kiore on the before dispersing to many of the smaller islands mainland (Atkinson 1989; Holdaway 1999). following the establishment of permanent Similarly, the shells of two species of large land Towns & Broome—History of rat eradications from New Zealand islands 379 Fig. 1 Map