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Help for Tonga's threatened native birds to fight back against the invasive rat

Biodiversity Conservation, BRB

Available Online

Moverley, David

Radio Australia

SPREP

Eradicating invasive rats to help protect native Tongan birds.

Rat eradication comes within a whisker! A case study of a failed project from the South Pacific

Biodiversity Conservation, BRB

Available Online

Amos. W

Brooke. M. de L

Churchyard. T

Nichols. H.J

To enhance their conservation value, several hundred islands worldwide have been cleared of invasive alien rats, Rattus spp. One of the largest projects yet undertaken was on 43 km2 Henderson Island in the Pitcairn group, South Pacific, in August 2011. Following massive immediate mortality, a single R. exulans was observed in March 2012 and, subsequently, rat numbers have recovered. The survivors show no sign of resistance to the toxicant used, brodifacoum. Using pre and post-operation rat tissue samples from Henderson, plus samples from around the Pacific, we exclude re-introduction as the source of continued rat presence. Microsatellite analysis of 18 loci enabled comparison of genetic diversity of Henderson rats before and after the bait drop. The fall in diversity measured by allele frequency change indicated that the bottleneck through which the breeding population passed was probably around 50 individuals, representing a census population of about 60-80 animals. This is the first failed project that has estimated how close it was to success.

Invasive rats on tropical islands: their population biology and impacts on native species

Available Online

Bunbury, Nancy

Harper, Grant. A,

The three most invasive rat species, black or ship rat Rattus rattus, brown or Norway rats, R. norvegicus and Pacific rat, R. exulans have been incrementally introduced to islands as humans have explored the worlds oceans. They have caused serious deleterious effects through predation and competition, and extinction of many species on tropical islands, many of which are biodiversity hotspots. All three rat species are found in virtually all habitat types, including mangrove and arid shrub land. Black rats tend to dominate the literature but despite this the population biology of invasive rats, particularly Norway rats, is poorly researched on tropical islands. Pacific rats can often exceed population densities of well over 100 rats ha?1 and black rats can attain densities of 119 rats ha?1, which is much higher than recorded on most temperate islands. High densities are possibly due to high recruitment of young although the data to support this are limited. The generally aseasonally warm climate can lead to year-round breeding but can be restricted by either density-dependent effects interacting with resource constraints often due to aridity. Apparent adverse impacts on birds have been well recorded and almost all tropical seabirds and land birds can be affected by rats. On the Pacific islands, black rats have added to declines and extinctions of land birds caused initially by Pacific rats. Rats have likely caused unrecorded extinctions of native species on tropical islands. Further research required on invasive rats on tropical islands includes the drivers of population growth and carrying capacities that result in high densities and how these differ to temperate islands, habitat use of rats in tropical vegetation types and interactions with other tropical species, particularly the reptiles and invertebrates, including crustaceans.

Invasive alien species surveys, Aleipata Islands, Samoa : Follow up visit to Nu'ulua

Available Online

GEF-PAS Invasive Alien Species Project

Between the 27th and 29th of October 2015 invasive alien species surveys were conducted as part of the GEF-PAS invasive alien species project/Samoa to help inform the Aleipata management Plan. As part of these surveys sticky traps were placed on Nuulua Island to detect the presence of Rattus sp. The sticky traps were checked after two nights with no evidence of rat presence. These sticky traps were left for a further 50 nights to increase the chances of detecting rat. As part of this return trip to Nuulua Island an incidental bird list was compiled and other species of interest (i.e. Yellow Crazy Ants and Coconut Crabs), were recorded when encountered.

Rat Eradication on the Island of Suwarrow

Available Online

Munro. E.

The Island of Suwarrow and its surrounding waters was declared a National Park in 1978 under the Conservation Act 1975. The legal opinion sought in 2001 clarifies that Suwarrow is Crown Land. Today, Suwarrow is under the jurisdiction of the National Environment Service (NES) since 2003, for the primary purpose of conserving, preserving, protecting and managing the natural resources of Suwarrow.

Special Issue on Tropical Island Conservation: Rat Eradication for Species Recovery. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

J.C. Russell ... [et al.]

Special Issue Article: Tropical rat eradicationNon-target species mortality and the measurement of brodifacoum rodenticide residues after a rat (Rattus rattus) eradication on Palmyra Atoll, tropical Pacific. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Berentsen. A.R

Eisemann. J.D

Howaldd. G .R.

Pitt. W.C

Shiels. A.B

Volker. S.F

Wegmann. A.S

The use of rodenticides to control or eradicate invasive rats (Rattus spp.) for conservation purposes has rapidly grown in the past decades, especially on islands. The non-target consequences and the fate of toxicant residue from such rodent eradication operations have not been well explored. In a cooperative effort, we monitored the application of a rodenticide, Brodifacoum 25W: Conservation, during an attempt to eradicate Rattus rattus from Palmyra Atoll. In 2011, Brodifacoum 25W: Conservation was aerially broadcasted twice over the entire atoll (2.5 km2) at rates of 80 kg/ha and 75 kg/ha and a supplemental hand broadcast application (71.6 kg/ha) occurred three weeks after the second aerial application over a 10 ha area. We documented brodifacoum residues in soil, water, and biota, and documented mortality of non-target organisms. Some bait (1419% of the target application rate) entered the marine environment to distances 7 m from the shore. After the application commenced, carcasses of 84 animals representing 15 species of birds, fish, reptiles and invertebrates were collected opportunistically as potential non-target mortalities. In addition, fish, reptiles, and invertebrates were systematically collected for residue analysis. Brodifacoum residues were detected in most (84.3%) of the animal samples analyzed. Although detection of residues in samples was anticipated, the extent and concentrations in many parts of the food web were greater than expected. Risk assessments should carefully consider application rates and entire food webs prior to operations using rodenticides.

Special Issue Article: Tropical rat eradication. Seabird recovery and vegetation dynamics after Norway rat eradication at Tromelin Island, western Indian Ocean. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Bastien. M

Danckwerts. D.K

M. Le Corre. M

Micol. T

Morey Rubio.C

Orlowski. S

Pinaud. D

Ringler. D

Seabirds are notoriously sensitive to introduced mammalian predators and eradication programs have benefitted seabird populations and their habitats on numerous islands throughout the world. However, less evidence is available from the tropics as to the benefits of rat eradication. Here, we report the seabird recovery and vegetation dynamics on a small coralline island of the tropical western Indian Ocean, eight years after Norway rat (Rattus norvegicus) eradication. Two species of seabirds were breeding before rat eradication (red-footed and masked boobies, Sula sula and Sula, dactylatra) and, in both species, the number of breeding pairs had an apparent increase of 22?23% per year after rat eradication. Such a high annual growth rate cannot be achieved by auto-recruitment only and our data suggest that immigration from other source populations never occurred in at least one of these species. We suggest that it is rather due to a rapid increase in breeding success, which rapidly increased the observed number of breeders since birds remained in the available-for-counting-as-breeders group for much longer. Two other species, the white tern (Gygis alba) and the brown booby (Sula leucogaster) were recorded breeding in 2014. The former species has not bred on the island since 1856 and the latter has never bred on the island. Plant cover (monospecific formation of the ruderal herb Boerhavia diffusa) dramatically increased from less than 30% of surface coverage to more than 70%. Although the initial restoration project was to eradicate all introduced mammals of the island simultaneously, house mouse (Mus musculus) eradication failed. Mouse density was high 8 years after rat eradication (32 mice/ha in dry season and 52 mice/ha in rainy season) but not higher than at a comparable tropical island of the region (Juan de Nova) where mice coexist with introduced black rats (Rattus rattus) and feral cats (Felis catus). These results are discussed in terms of the direct positive effects of rat eradication on seabirds and plants and the indirect positive effects of post-eradication seabird increase on soil manuring and vegetation recovery. Overall, our results show that on tropical islands, seabird and habitat recovery can be very rapid after rat eradication and should be implemented as a restoration tool wherever possible.

Special Issue Article: Tropical rat eradication. The next generation of rodent eradications: Innovative technologies and tools to improve species specificity and increase their feasibility on islands. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Baxter. G.S.

Beek. J

Campbell K.J

Eason C.T

Glen A.S

Godwin. J

Gould. F

Holmes. N.D

Howald. G.R

Madden F.M

Ponder J.B

Threadgill. D.W

Wegmann. A.S

Rodents remain one of the most widespread and damaging invasive alien species on islands globally. The current toolbox for insular rodent eradications is reliant on the application of sufficient anticoagulant toxicant into every potential rodent territory across an island. Despite significant advances in the use of these toxicants over recent decades, numerous situations remain where eradication is challenging or not yet feasible. These include islands with significant human populations, unreceptive stakeholder communities, co-occurrence of livestock and domestic animals, or vulnerability of native species. Developments in diverse branches of science, particularly the medical, pharmaceutical, invertebrate pest control, social science, technology and defense fields offer potential insights into the next generation of tools to eradicate rodents from islands. Horizon scanning is a structured process whereby current problems are assessed against potential future solutions. We undertook such an exercise to identify the most promising technologies, techniques and approaches that might be applied to rodent eradications from islands. We highlight a Rattus-specific toxicant, RNA interference as species-specific toxicants, rodenticide research, crab deterrent in baits, prophylactic treatment for protection of non-target species, transgenic rodents, virus vectored immunocontraception, drones, self-resetting traps and toxicant applicators, detection probability models and improved stakeholder community engagement methods. We present a brief description of each method, and discuss its application to rodent eradication on islands, knowledge gaps, challenges, whether it is incremental or transformative in nature and provide a potential timeline for availability. We outline how a combination of new tools may render previously intractable rodent eradication problems feasible.

Special Issue Article: Tropical rat eradication. Improving the odds: Assessing bait availability before rodent eradications to aid in selecting bait application rates. Biological Conservation. Volume 185, May 2015

Biodiversity Conservation, BRB

Available Online

Berentsen. A.R

Brooke. M.L

Cuthbert. R.J

Griffiths. R.

Holmes. N.D

Howald. G.R

Pitt. W.C

Pott. M

Ramos-Rend¢n. G

Russell. J.C

Samaniego-Herrera. A

Wegmann. A.S

Rodent eradications undertaken on tropical islands are more likely to fail than eradications undertaken at higher latitudes. We report on 12 independent rodent eradication projects undertaken on tropical islands that utilized the results of an in situ bait availability study prior to eradication to inform, a priori, the bait application rate selected for the eradication. These projects also monitored bait availability during the eradication. The results from our analysis verified the utility of bait availability studies to future rodent eradication campaigns and confirmed the influence of two environmental factors that can affect bait availability over time: precipitation prior to the study and the abundance of land crabs at the study site. Our findings should encourage eradication teams to conduct in-depth assessments of the targeted island prior to project implementation. However, we acknowledge the limitations of such studies (two of the projects we reviewed failed and one removed only one of two rodent species present) and provide guidance on how to interpret the results from a bait availability study in planning an eradication. Study design was inconsistent among the twelve cases we reviewed which limited our analysis. We recommend a more standardized approach for measuring bait availability prior to eradication to provide more robust predictions of the rate at which bait availability will decrease during the eradication and to facilitate future comparisons among projects and islands.

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