Rodent control in the conservation of endangered species
The commensal rodent pest species have spread from their ancestral homes in Asia to inhabit many natural ecosystems worldwide. The introduction of these exotics has often had a significant effect on endemic plant and animal species but their impact has, perhaps, been most severe on off-shore and oceanic islands where nesting birds, insects, terrestrial molluscs, reptiles and amphibians are all vulnerable. Conservationists have used a variety of control approaches either to reduce or eliminate the pressure of competition and predation exerted by introduced rodents on island populations of endangered species. Successful projects have involved a sequence of carefully-planned operations. Firstly, an assessment of the nature and scope of the rodent threat is undertaken to permit the development of a control programme with the maximum chance of success. A second element is the estimation of the likely impact of intended control operations on non-targets in these highly sensitive environments. A pilot study may be required prior to the third and final stage, that of implementation and then monitoring the effect of the programme on target pests, sympatric non-targets and the species that are the object of the conservation effort. The anticoagulant rodenticide brodifacoum (trade names 'Klerat' and 'Talon') is used in conservation projects worldwide. This paper puts forward general principles for adoption when employing this compound for conservation and exemplifies the approach advocated with descriptions of a number of projects undertaken for the benefit of a variety of endangered species.