Article

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.

Wedelia, creeping oxeye, or the trailing daisy, a deceptively beautiful, bright emerald-green creeper with bright yellow daisy-like flowers, is one of the world's most aggressive weeds and is listed among these other destructive organisms as one of the worlds 1000 worst invasive alien species. IT is now firmly established in Melanesia and throughout the Pacific islands.

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.

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.

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.

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.

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 Kuramoo, or Blue Lorikeet (Vini peruviana), is listed by IUCN as threatened. Formerly, the species was widespread on the Society and Tuamotu ISlands, but it became extinct on Tahiti, Moorea and other large islands in the Society Group early this century and is now also extinct on many other islands on which it once occurred. Today, in French Polynesia, it apparently survives only on two small islands in the Society Group and several in the Tuamotu Group.

During a survey of the birds of the Cook Islands from July-September 1973, the birds of the islands of Atiu, Mitiaro, Mauke and Mangaia were investigated for the first time. Series of seven land birds that apparently represent undescribed forms were collected. This paper gives descriptions of these forms, in advance of a fuller report on their biology and that of the other birds seen.