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Feasibility Plan to Eradicate Common Mynas (Acridotheres Tristis) From Feasibility Plan to Eradicate Common Mynas ( Acridotheres tristis ) from Mangaia Island, Cook Islands John Parkes Landcare Research PO Box 40, Lincoln 7640 New Zealand Landcare Research Contract Report: LC0506/184 PREPARED FOR: Tapororoanga Ipukurea Society PO Box 649 Avarua, Rarotonga Cook Islands DATE: September 2006 Reviewed by: Approved for release by: Jane Lattimore Andrea Byrom Scientist Science Leader Landcare Research Wildlife Ecology and Epidemiology 3 Contents Summary ...........................................................................................................................5 1. Introduction .......................................................................................................................6 2. Methods.............................................................................................................................7 3. Impacts of Mynas..............................................................................................................8 3.1 Impacts on native animals........................................................................................8 3.2 Mynas as vectors of weeds and diseases..................................................................9 3.3 Impacts on people ..................................................................................................10 4. Feasibility of Eradication ................................................................................................10 4.1 Lessons from past attempts....................................................................................10 4.2 Feasibility planning................................................................................................11 5. Control Options...............................................................................................................15 5.1 Review of options ..................................................................................................15 5.2 Primary control – poisoned baits ...........................................................................15 5.3 Secondary control of survivors ..............................................................................17 6. An Eradication Strategy ..................................................................................................18 6.1 Preparation and training.........................................................................................19 6.2 Initial knockdown phase ........................................................................................20 6.3 Secondary phase.....................................................................................................21 6.4 Stop rules and surveillance phase ..........................................................................21 6.5 Operational monitoring..........................................................................................22 7. Measuring Benefits and Consequences...........................................................................22 7.1 Benefits to biodiversity..........................................................................................22 7.2 Social benefits........................................................................................................22 7.3 Adverse consequences of success..........................................................................22 8. Conclusions and Recommendations................................................................................22 8.1 Is eradication of mynas justified? ..........................................................................22 8.2 Is eradication feasible?...........................................................................................23 8.3 What needs to be resolved before beginning an attempt?......................................23 8.4 What would it cost?................................................................................................23 8.5 Border control ........................................................................................................24 8.6 Information campaign............................................................................................24 9. Acknowledgements .........................................................................................................24 10. References .......................................................................................................................24 Appendix 1 Current known distribution of common mynas in the Pacific. Unless stated the information is taken from the ISSG database (M. Browne, pers. comm.). ..................................................................................................................27 Landcare Research 4 Landcare Research 5 Summary Common mynas ( Acridotheres tristis ) have been introduced (often as a biocontrol for insects) or colonised many islands in the Pacific. They are one cause of decline in some native bird species such as endemic kingfishers, and are a pest when they damage fruit and compete for food put out for domestic animals. The Taporoporoanga Ipukarea Society (TIS) of the Cook Islands proposes to eradicate mynas from Mangaia Island (5180 ha) to protect kingfishers and commissioned this study to determine whether this is feasible and what would need to be done to reduce the risks of failure or overcome constraints during such an attempt. The Pacific Invasives Initiative supported this study partly because of the potential biodiversity and societal benefits to Mangaia, but partly to act as a demonstration for the management of mynas on other islands. The report concludes that eradication of mynas is justified and technically feasible. Three operational phases are likely to be required. The first is on initial knockdown that targets all mynas using toxic baits. The second phase would involve locating and killing survivors of the initial knockdown using a variety of control tools. The third phase requires ongoing surveillance (and reaction if required) until it is clear no mynas remain. The first phase would be conducted over about 2 months during winter. The second phase should be planned to end before the following winter, and the third phase will depend on whether this succeeds. The attempt would be novel at this scale, and so has an unresolved element of technical risk. These risks of failure or of adverse consequences are identified and ways suggested to minimise them. Constraints on the use of the preferred technique for the initial phase – the use of an avicide called DRC1339 – are identified as largely the risk to non-target domestic animals such as chickens, and these can be avoided. It is estimated that the costs to achieve eradication with appropriate levels of monitoring would be about NZ$100,000. Two risks remain to be resolved. First, while the Mangaia Resource Council has approved the development of this feasibility plan and initial surveys of where mynas roost, they will need to give their final consent to proceed once they have seen the plan. There was general, although not unanimous, community support to get rid of the mynas expressed at preliminary meetings on the island. Second, there is an unresolved risk from the lack of experience in bird control and in large- scale project eradication project management by the TIS. This can be resolved by including appropriate technical advisors in the project delivery team, along with TIS and local people. A cause of many past failures to eradicate pests from islands when even the best method fails to kill 100% in the initial control effort has been lack of commitment and a process to deal with survivors. Sustaining a presence on the island by TIS staff (they live in Rarotonga) may be difficult during this secondary phase of the operation. Landcare Research 6 1. Introduction Mangaia Island (5180 ha) is the second largest island in the Cook Islands. It is located 200 km from Rarotonga and has a population of about 700 people. The island is a makatea (raised coral reef) but is interesting because the original volcano has remerged in the past and provided rich volcanic soils amid the fossil coral. Common mynas were first introduced to Mangaia in the early 20 th century but did not establish invasive populations until a major release of birds from Rarotonga, made in 1964 in response to the damage to coconuts by a stick insect ( Graeffea crouanii ). Common mynas ( Acridotheres tristis ) and their cousins the jungle myna ( A. fuscus ) are native to India but have been introduced or subsequently invaded many countries (Long 1981; Lever 1987) including many islands in the Pacific (Appendix 1). Despite earlier support for mynas as a means of biocontrol of insect pests and a perception that, at least in some cases, the birds may have controlled the insects, mynas today are generally seen throughout the Pacific at best as a nuisance and at worst as a serious pest. Common and jungle mynas continue to expand their range either naturally (Upolu to Savai’i) or by hitching rides on ships (Upolu to Fakaofo). The common myna is listed as one of the world’s worst invasive species (IUCN 2000), and several island states with mynas have expressed a desire to eradicate or control them. However, this is easier said than done! The Pacific Invasives Initiative (PII) received three proposals to eradicate mynas: one to eradicate a very recent introduction of a few birds on Fakaofo Atoll in the Tokelau Islands (the birds turned out to be jungle mynas), one to eradicate the
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