Offshore Islands Conservation Programme ANTIGUA & BARBUDA Feasibility study for the eradication of black rats Rattus rattus from Redonda, with new observations on the island’s biodiversity and ecology By ELIZABETH A. BELL Wildlife Management International Limited and JENNY C. DALTRY Fauna & Flora International 2012 Cover illustrations: Red‐footed boobies (Adam Long, British Mountaineering Council); Redonda (Jenny Daltry, Fauna & Flora International – Offshore Islands Conservation Programme); Black rat eating prickly pear on Redonda (John Cancalosi, Fauna & Flora International); Turk’s cap cactus (Dave Turnbull, British Mountaineering Council). THE OPINIONS OF THE AUTHORS DO NOT NECESSARILY REFLECT THE OPINIONS OF THE PARTNER ORGANISATIONS OF THE OFFSHORE ISLANDS CONSERVATION PROGRAMME. PUBLISHED BY Offshore Islands Conservation Programme St. John’s, Antigua RECOMMENDED CITATION Bell, E.A. & Daltry, J.C. (2012) Feasibility Study for the Eradication of Black Rats Rattus rattus from Redonda, with New Observations on the Island’s Biodiversity and Ecology. Report from Wildlife Management International Ltd and Fauna & Flora International to the Offshore Islands Conservation Programme, St John’s, Antigua and Barbuda. The award-winning Offshore Islands Conservation Programme (OICP) was established in 1995 as the Antiguan Racer Conservation Project, and operates under a Memorandum of Understanding between the Government of Antigua and Barbuda, Environmental Awareness Group, Durrell Wildlife Conservation Trust, Fauna & Flora International, Island Resources Foundation and Black Hills State University. This partnership is working towards the Vision of healthy, functioning coastal ecosystems that are sustainably managed for the conservation of native wildlife and for the benefit of local people. Our activities include environmental education, endangered species management, invasive species control, habitat restoration, research and monitoring, and strengthening local governance and management capacity. This study was funded under the US Fish & Wildlife Service’s Neotropical Migratory Bird Conservation Act (grant no. F10AP00785, “Conserving Antigua’s Most Critical Bird Habitats). Contact details: Ms. Elizabeth ‘Biz’ Bell Dr. Jenny Daltry, FRGS Ms. Natalya Lawrence Senior Ecologist Senior Conservation Biologist, Project Coordinator Wildlife Management International Ltd Fauna & Flora International Offshore Islands Conservation PO Box 45, Jupiter House, Programme Spring Creek Station Road Environmental Awareness Group Marlborough 7244 Cambridge CB1 2JD PO Box 2103, St John’s New Zealand United Kingdom Antigua, West Indies www.wmil.co.nz www.fauna-flora.org www.eagantigua.org Email: [email protected] Email: [email protected] Email: [email protected] EXECUTIVE SUMMARY Rodents have been successfully eradicated from hundreds of islands ranging in size from 1 to 11,200 hectares throughout the world, including more than 20 islands in the Caribbean. These cases demonstrate how safely and effectively rats can be eliminated, and the remarkable benefits their removal can bring to both wildlife and people. Some of the best examples are in Antigua and Barbuda, where a dozen islands have been cleared of alien invasive black rats Rattus rattus since 1995. In recent years, a number of organisations and individuals, including technical staff of the Environmental Awareness Group and Government of Antigua and Barbuda, have put forward the idea of eradicating rats from Redonda to support the recovery and conservation of the island’s biodiversity. At approximately 53 ha, planar area (or circa 80 ha, surface area), Redonda is one of the largest islands in Antigua and Barbuda and has been identified in the national land use plan as a priority site for environmental conservation. This report presents the findings of a study to determine the methods and cost of eradicating rats from Redonda, and examines the possible benefits this could bring to wildlife and people. The study entailed a trip to Redonda from 10-14 April and 18 April 2012, a literature review, and a series of consultations with key government and non-governmental stakeholders on Antigua. While the main focus of our study was on the rats, this report also contains new information on the status and ecology of native wildlife and the feral goats on Redonda, which will also assist with conservation planning. Redonda has been formally recognised as an Important Bird Area and supports rare and unique animals and plants of both national and global importance. At least three endemic lizards still remain: Redonda ground lizards Ameiva atrata, Redonda tree lizards Anolis nubilus and an unnamed dwarf gecko Sphaerodactylus sp.; all of which qualify as globally threatened according to the findings from this survey. Birds include regionally, even globally, significant colonies of brown boobies (774 pairs), masked boobies (164 pairs), red-footed boobies (over 150 pairs) and magnificent frigatebirds (119 pairs), plus smaller numbers of red-billed tropicbirds, brown noddies and bridled terns. However, the seabird colonies appear smaller and less diverse than they ought to be, and there is a dearth of terrestrial birds - only two peregrines and a few zenaida doves were observed in April 2012. Seventy species of plants and a few invertebrates have been recorded, but some species are also feared to be extinct and more extensive surveys are warranted. No amphibians or native mammals have been recorded. The Eurasian black rats on Redonda are unusually large and their density is exceptionally high. Use of trapping lines indicated that Redonda has at least 70 rats per hectare, or a total population of approximately 5,500 rats. Only black rats are known to be present: brown rats R. norvegicus and house mice Mus musculus were not detected during this or previous studies and it appears that previous reports of brown rats were in error. The omnivorous black rats are having a very severe impact on the wild animals and plants of Redonda. Rats were observed killing seabird chicks larger than themselves, while autopsies of trapped rats found the rats eating a wide range of food items including various plants, seabird eggs and chicks, lizards and goat droppings. Many native birds, reptiles, plants and invertebrates have already disappeared, and many remaining species are now critically scarce. Species not seen for many years include the last Antiguan burrowing owls Athene cunicularia amaura and the endemic Redonda skink Copeoglossum redondae. Their decline is almost certainly linked to predation by rats. The island’s high density of rats, remote location and very rugged terrain presents a number of challenges. As described in this report, the research team carried out a full site assessment, measured rat density and distribution, identified and evaluated risks, difficulties and mitigation measures, conducted bait trials to test whether the rats would accept rodenticide, identified non-target species, and evaluated different 1 methods and materials. This assessment concludes that the eradication of black rats from Redonda is technically feasible, and this report outlines the set out the operational options and technical requirements for the proposed eradication. The aim of the proposed operation should be to eradicate all rats from Redonda while minimising any adverse impacts on the environment, non-target species and people. It is recommended that the eradication takes place outside the hurricane season, ideally January to April, in a combined aerial and ground- based operation using rodenticide containing the anticoagulant brodifacoum. The proposed eradication techniques have proven to be safe and effective and are supported by similar operations in the Caribbean and around the world. Up to 13 persons will be required to complete this work effectively: five helicopter team members (including pilot and ground crew) and eight ground-based operators. Additional persons will be required to monitor wildlife, logistical support, communications and outreach on Antigua & Barbuda and Montserrat. This rat eradication operation would involve a number of stages. Necessary tasks include: (i) produce a detailed Operational Plan; (ii) obtain required permits and approvals; (iii) continue stakeholder consultation; (iv) prepare tenders and contracts; (v) establish monitoring and research programmes; (vi) appoint eradication personnel; (vii) purchase all equipment and bait; (viii) implement the rat eradication (i.e. baiting and evaluation); (ix) develop and implement a post-eradication biosecurity strategy to prevent rats and other species from (re)invading Redonda; and (x) design and implement long-term monitoring of flora and fauna species and the ecosystem to measure the effects of the rat eradication. It may also be necessary to (xi) move some of the endemic lizards to a temporary ex-situ facility on Antigua during the eradication operation to remove any risk of direct or secondary poisoning. Monitoring to detect any surviving or invading rats should also be continued, with a final evaluation of the success of the eradication carried out after two years. Taking into account the relatively large size of Redonda and its remote location, rugged terrain, high transport costs and lack of infrastructure, the rat eradication operation would cost approximately US$250,000. We recommend allocating up to US$630,000 over four years to include necessary pre- and post-eradication monitoring, biosecurity, contingency costs and a temporary ex-situ facility