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Special Issue Article: Tropical rat eradicationBest practice guidelines for rat eradication on tropical islands. Biological Conservation. Volume 185, May 2015

Island and Ocean Ecosystems, BRB

Available Online

Boudjelas. S

Broome. K

Cranwell. S

Griffiths. R

Keitt. B

Millett. J

Pitt. W

Samaniego-Herrera. A.

Invasive vertebrates are a leading cause of the extinction on islands and rats (Rattus spp.) are one of the most damaging to island ecosystems. Methods to eradicate rates from islands are well established and there have been over 580 successful eradications to date. Increasingly, rat eradications are being implemented on tropical islands, a reflection of the need to protect the threatened biodiversity in the tropics. Yet rat eradications on tropical islands fail more frequently than those in temperate climates. In an effort to identify the main reasons for the lower success rate on tropical islands and possible solutions, a workshop was convened with the 34 experts in rat eradication, tropical rodent and island ecology and toxicology. The workshop focused on projects using aerial broadcast of brodifacoum, a 2nd generation anticoagulant, because this approach had provided the highest success rate for eradicating rodents from islands. The workshop participants reviewed previously identified challenges to successful rat eradications on tropical islands including increased insect and crab densities resulting in competition for bait, year round or unpredictable timing of breeding rats and increased or unpredictable availability of alternative, natural foods. They also identified a number of new, likely reasons for the lower success rate on tropical islands and provided recommendations for how to address these risks in the planning and implementation of rat eradications. While the success rate of aerial broadcast rat eradications in tropical environments is quite high at 89%, it is hoped that by following the recommended best practices provided in this paper, future success rates will be closer to the 96.5% demonstrated for aerial broadcast rat eradication on temperate islands.

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

Island and Ocean Ecosystems, 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

Island and Ocean Ecosystems, 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 eradication. Trophic roles of black rats and seabird impacts on tropical islands: Mesopredator release or hyperpredation? Biological Conservation. Volume 185, May 2015

Island and Ocean Ecosystems, BRB

Available Online

Le Corre. M.

Ringler. D

Russell. J.C

Rats contribute to the decline of tropical seabird populations by affecting their breeding success through direct predation of eggs and chicks. When they coexist with other predators, invasive rats may also generate indirect interactions via the changes they impose on the structure of communities and trophic interactions following invasion (hyperpredation process), or when apex predators are eradicated from the ecosystem (mesopredator release effect). Understanding these effects is necessary to implement restoration operations that actually benefit threatened seabird populations. We investigated these processes on two French tropical seabird islands of the western Indian Ocean, Europa and Juan de Nova, where black rats coexist with two different apex predator species (introduced cats and potentially native barn owls). The parallel use of several methods (diet analysis, stable isotopes, seabird monitoring) to identify trophic roles of rats revealed that the direct impact of rats on seabirds was particularly high on Europa where only rats and owls occur, with high consumption of chicks resulting in low breeding success for several seabird species. We also suggested that hyperpredation associated with top-down regulation of cats is occurring on Juan de Nova, although territoriality of cats may buffer this process. Conversely we found evidence that mesopredator release effect is unlikely, irrespective of the apex predator identity. Considering the most likely effects on both islands we provided recommendations on eradication priorities to mitigate the risk of local extinction that seabirds are currently facing.

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

Island and Ocean Ecosystems, 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.

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.

Restoration of Nu'utele and Nu'ulua Islands (Aleipata group), Samoa, through the management of introduced rats and ants

Available Online

Tye, A. & Butler, D. J.

Status of birds, peka (flying foxes) and reptiles on Niue island

Available Online

Butler, D.J.

Powlesland, R.G.

Westbrooke, I.M.

During 1021 September, quantitative surveys were carried out of birds and flying foxes using the same techniques as applied in earlier surveys, and searches carried out for a rare parrot and lizard. Bird counts showed that the lupe or Pacific imperial-pigeon population has recovered following a decline between 1994 and 2004 though the current hunting rate is considered unsustainable. Miti or Polynesian starling numbers have gradually declined over the period 19942012 which is a concern and hard to explain. Rat predation is a possible cause. There was also an indication that pekapeka or white-rumped swiftlet numbers have declined though more investigation is needed to confirm this. We were unable to find any hega or blue-crowned lory though a few individuals were reported to us. Numbers are clearly very low and the next step must be to gain a better understanding of where the species regularly occurs so that management can be applied.

Restoration of Nu'utele and Nu'ulua Islands (Aleipata Group), Samoa through the management of introduced rats and ants - CEPF final project completion report

Island and Ocean Ecosystems, BRB

Available Online

Tye, Alan

Encyclopedia of biological invasions.

Island and Ocean Ecosystems, BRB

Rejmanek, Marcel

Simberloff, Dadniel

This encyclopedia illuminates a topic at the forefront of global ecology - biological invasions, or organisms that come to live in the wrong place. Written by leading scientists from around the world, the book addresses all aspects of this subject at a global level - including invasions by animals, plants, fungi, and bacteria - in succinct, alphabetically arranged articles. Scientifically uncompromising, yet clearly written and free of jargon, the volume encompasses fields of study including biology, demography, geography, ecology, evolution, sociology, and natural history and features many cross-references, suggestions for further reading, illustrations, an appendix of the world's worst 100 invasive species, a glossary, and more. The book features articles on well-known invasive species such the zebra mussel, chestnut blight, cheatgrass, gypsy moth, Nile perch, giant African snail, and Norway rat and details regions with especially large numbers of introduced species including the Great Lakes, Mediterranean Sea, Hawaiian Islands, Australia and New Zealand. This work will be of great value in ecology and conservation science. Invasive species are a severe and exponentially growing problem of the environment, and one difficult even to characterize, much less contain.-Edward O. Wilson, author and scientist "Second only to habitat loss mixed with climate disruption, invasive species represent the next most serious threat to biodiversity. The Encyclopedia of Biological Invasions, written by an impressive group of experts, now makes available to conservation biologists, managers, decision makers, and concerned citizens a comprehensive single source of this key topic."-Paul R. Ehrlich, co-author of The Dominant Animal

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