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Special Issue Article: Tropical rat eradication. The response of black rats (Rattus rattus) to evergreen and seasonally arid habitats: Informing eradication planning on a tropical island. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Grant A. Harper

James C. Russell

Martijn van Dinther

Nancy Bunbury

Rat eradications on tropical islands have been less successful than operations in temperate climates. This is likely due to poor understanding of the factors unique to tropical regions that rat populations respond to, such as high numbers of land crabs, aseasonal climates and habitats not found at higher latitudes. On Aldabra Atoll, southern Seychelles, black rats were monitored for one year in three habitats over three climatic seasons to investigate changes in density and breeding to inform planning for a possible rat eradication. Rats bred all year in mangrove forest and in two of three seasons, including the dry season, in Pemphis forest, probably resulting from the saline tolerance of these habitats: lush vegetation and seeds were available there during the dry season. In contrast, rats from the adjacent mixed-scrub habitat only bred in the wet season due to desiccation of vegetation and lack of fresh water during other times of the year. Bait consumption trials showed that all rats ingested dyed bait when applied at 15 kg/ha, despite high rat densities and substantial bait interference by non-target species, but not at an application rate of 10 kg/ha. A novel bola technique was tested for distributing bait into mangrove forest, where aerially applied rat bait would normally be lost due to tidal inundation. The method is likely to improve rat exposure to bait in mangrove forest and other habitats on tropical islands, and warrants further development.

Special Issue Article: Tropical rat eradication. Invasive rat interactions and over-invasion on a coral atoll. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Anderson S.H

Caut. S

Lee. M.

Russell. J.C

Invasive rats are found on most island groups of the world, and usually more than one species has invaded. On tropical islands populations of different invasive rat species can co-exist on very small islands, but the population dynamics of such co-existing rat species, their impact on each other, and the mechanisms of coexistence are not well known. This lack of knowledge is a barrier to improving the success rate of tropical island rat eradications. Through an exhaustive trapping eradication campaign on a small tropical island, we study the population structure of historically established Rattus exulans where R. rattus have colonised within the last fifty years and over-invaded. We contrast this R. exulans population with a nearby island population where R. exulans exist alone. Recently invaded R. rattus numerically and morphologically dominate R. exulans; however stable isotope analyses show that the trophic position of R. exulans remains consistent regardless of the presence of R. rattus, once differences in trophic foundations of islands are accounted for. Although the trophic position of both rat species is indistinguishable, R. rattus is able to dominate R. exulans through interference competition. Our eradication attempt was interrupted by a tropical cyclone and ultimately unsuccessful, but there is some evidence that R. rattus reduced control device availability to R. exulans, which has important implications for multi-species control operations.

Special Issue Article: Tropical rat eradicationFactors associated with rodent eradication failure. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Alifano. A

Griffiths.R

Holmes. N.D

Pott. M

Russell. J.C.

Wegmann. A.S

Will.D

Invasive rodents have an overwhelmingly detrimental impact to native flora and fauna on islands. Rodent eradications from islands have led to valuable biodiversity conservation outcomes. Tropical islands present an additional suite of challenges for rat eradications due to unique characteristics associated with these environments. To date tropical island rat eradications have failed at a higher rate than those undertaken outside the tropics. Critical knowledge gaps exist in our understanding of what drives this outcome. We collated an in-depth dataset of 216 rodenticide based rat eradication operations (33% of all known rodent eradications) in order to determine correlates of eradication failure, including both project implementation factors and target island ecology, geography and climate. We assessed both failed and successful projects, and projects inside and outside the tropics, using random forests, a statistical approach which compensates for high dimensionality within, and correlation among, predictor variables. When assessing all projects, increasing mean annual temperature, particularly above 24 °C, underscored the higher failure rate and greater difficulty of rodent eradications on islands in lower latitudes. We also found clear trends in eradication failure for factors unique to the tropics, including the presence of land crabs burrowing and hermit crabs, and coconut palms (Cocos nucifera). The presence of agriculture was also associated with failure. Aerial operations had a higher success rate than ground-based methods but success with this technique was less likely in the presence of hermit crabs and other non-target bait consumers. Factors associated with failure in ground-based eradication methods suggested limitations to project scaling such as island area and number of staff. Bait station operations were less likely to succeed when using stopping rules based on measures of rodent abundance. Factors influencing rat eradication failure in tropical environments continue to require a deeper understanding of tropical island dynamics to achieve a higher rate of eradication success.

Feasibility Assessment for the Removal of Pacific Rats (Rattus exulans) from Late Island. Reports 1 & 2

Bonham, J.

Griffiths, R.

Island Conservation

Predator-Free Rakiura. An economic appraisal.

Available Online

Morgan, Gareth

Simmons, Geoff

This report estimates the benefits of making Rakiura and surrounding islands predator free. The proposal is to do this in two phases, starting with the Halfmoon Bay area (denoted in this report as HMB) before progressing to the rest of the island (denoted in this report as full).

Feasibility Assessment for the Removal of Pacific Rats (Rattus exulans) from Late Island

Available Online

Bonham. J

Griffiths. R.

Late is an isolated and uninhabited island located about 55 km WSW of the island of Vava'u, in the Kingdom of Tonga. Late supports a tropical broad-leaf forest ecosystem, one of the most threatened ecosystem types in the world and one of the best remaining tracts of diverse native forest in Tonga. Owing to its relatively unmodified forest communities, Late is also a global stronghold for two IUCN listed species of bird, one native mammal, and six species of reptile.

Onotoa Island Myna Management Report

Available Online

Teremita. K.

This report is based on official trip made to Onotoa early this year 2014. IAS project under ECD together with ALD from MELAD was made to fulfill the obligation of ECD as an implementing agency. In 2012, there is a survey trip made to confirm the distribution and number of myna birds on Onotoa in order to set up appropriate actions to cease the disturbances and destruction caused by this bird. Thus, the programs of this trip are to educate the locals on how to construct myna (mynah) bird traps and to encourage instinctive knowledge for eradication using their own resources and conduct an outreach program on inter-island bio-security role. This report therefore will highlight activities, findings and data update on numbers, challenges and recommendations that will aim to improve upcoming responses.

Operational Plan for the eradication of Pacific Rats (Rattus exulans) from Late Island

Available Online

Bonham, J.

Griffiths, R.

This plan sets out the operational detail, logistics and framework for a planned eradication of introduced Pacific rats from Late Island (1,731ha) in the Kingdom of Tonga. The method for the eradication is the delivery of grain-based bait containing the anticoagulant brodifacoum, into every potential rodent territory on the island. This will be done during the driest part of the year when rodents are potentially most vulnerable due to lower relative availability of natural food supplies. Because of the islands size and complex topography, the bait will be applied aerially using a helicopter with an underslung bait spreading bucket. Aerial application has been successful in eradicating rodents from many islands around the world, and the logistics and methodology are based upon similar successful operations. Mitigation measures will be required for key non-target species, especially the Friendly-ground dove. Monitoring of rodents and native species before and after the operation will be required to assess the success and effect of the operation.

Operational Plan Toloa Rainforest Restoration Project 2014-2020

Climate Change Resilience, BRB

Available Online

James Atherton

The Operational Plan for the Toloa Rainforest Restoration Project was prepared for the Ministry of Environment, Energy, Climate Change, Disaster Management, Meteorology, Information and Communication (MECCDMMIC), Tupou College and other partners under the Global Environment Facility Pacific Alliance for Sustainability (GEF-PAS) funded Prevention, control and management of invasive alien species in the Pacific Islands project.

Valuing the impact of selected invasive species in the Polynesia-Micronesia hotspot, final report

Available Online

Aalbersberg, Bill

Boudjelas, Souad

Brown, Pike

Daigneault, Adam

Greenhalgh, Suzie

Mather, John

Nagle, William

Invasive species pose an enormous threat in the Pacific: not only do they strongly affect biodiversity, but they also potentially affect the economic, social, and cultural wellbeing of Pacific peoples. Invasive species can potentially be managed and that their impacts can potentially be avoided, eliminated, or reduced. However, neither the costs nor the numerous benefits of management are well understood in the Pacific. Thus, the goals of this project were: A) to account for both the costs and benefits of managing invasive species; B) to prepare empirically grounded advocacy materials to help increase investment in the management of invasive species; C) to help governments prioritise investment in managing these species; and D) to build capability for undertaking economic assessments in the future. To accomplish these goals, we undertook cost-benefit analyses (CBAs) of managing five species that are well established on Viti Levu, Fiji: spathodea campanulata (African tulip tree), herpestus javanicus (small Asian mongoose), papuana uninodis (taro beetle), pycnonotus cafer (red-vented bulbul), and merremia peltata (merremia vine). Next, we conducted a comprehensive training programme on the CBA for invasive species management for professionals from the Pacific. Third, we collaborated with Pacific organisations to develop a uniform guide to conducting CBAs with numerous examples from the region. We also designed a flexible Microsoft Excel-based tool for conducting CBAs, enabling professionals who did not attend the training course to nevertheless undertake rigorous CBAs on invasive spsecies management. Finally, we developed advocacy material and publicised findings from this project to promote investment in invasive species management. This report details these activities in turn. It also includes numerous appendices that include the tools, guidance documents, and advocacy materials developed under this project.

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