RESUMEN
Introduced brushtail possums (Trichosurus vulpecula) and rat species (Rattus spp.) are major vertebrate pests in New Zealand, with impacts on conservation and agriculture being managed largely through poisoning operations. Aerial distribution of baits containing sodium fluoroacetate (1080) has been refined to maximise cost effectiveness and minimise environmental impact, but this method is strongly opposed by some as it is perceived as being indiscriminate. Although ground based control enables precise placement of baits, operations are often more than twice as costly as aerial control, mainly due to the high labour costs. We investigated a new approach to ground based control that combined aerial distribution of non-toxic 'prefeed' baits followed by sparse distribution of toxic baits at regular intervals along the GPS tracked prefeeding flight paths. This approach was tested in two field trials in which both 1080 baits and cholecalciferol baits were used in separate areas. Effectiveness of the approach, assessed primarily using 'chewcards', was compared with that of scheduled aerial 1080 operations that were conducted in outlying areas of both trials. Contractors carrying out ground based control were able to follow the GPS tracks of aerial prefeeding flight lines very accurately, and with 1080 baits achieved very high levels of kill of possums and rats similar to those achieved by aerial 1080 baiting. Cholecalciferol was less effective in the first trial, but by doubling the amount of cholecalciferol bait used in the second trial, few possums or rats survived. By measuring the time taken to complete ground baiting from GPS tracks, we predicted that the method (using 1080 baits) would be similarly cost effective to aerial 1080 operations for controlling possums and rats, and considerably less expensive than typical current costs of ground based control. The main limitations to the use of the method will be access to, and size of, the operational site, along with topography and vegetation density.
Asunto(s)
Fluoroacetatos/toxicidad , Especies Introducidas , Control de Plagas , Plaguicidas/toxicidad , Venenos , Trichosurus , Animales , Aviación , Fluoroacetatos/economía , Masculino , Nueva Zelanda , Plaguicidas/economía , RatasRESUMEN
BACKGROUND: The metabolic toxin sodium fluoroacetate ('compound 1080') is widely used for controlling introduced mammalian pests in New Zealand. For large-scale operations, 1080 is distributed aerially in bait to kill brushtail possums (Trichosurus vulpecula Kerr) and ship rats (Rattus rattus L.). While usually successful in reducing pest populations by > 80%, widespread distribution of toxic bait is relatively expensive and raises concerns from some members of the public. Here, trials with spatial aggregation of baits in forested habitats were conducted to determine whether this can reduce toxin usage while maintaining operational efficacy. RESULTS: When 1080 baits were aggregated into clusters (by hand sowing) or into strips (by precision aerial deployment), indices of possum relative abundance were reduced by 92-100%, compared with 73-100% reductions using conventional aerial broadcasting, while all methods reduced relative abundance indices of rats by 88% or greater. Radio tracking indicated a kill rate of > 90% against possums, regardless of bait distribution method. CONCLUSIONS: Simply by modifying bait distribution patterns, spatial aggregation can be used to maintain the high encounter rate of pests with 1080 bait that is necessary for operational efficacy, while reducing current toxin usage by up to 80%. Aggregated bait delivery could have relevance for other mammalian pest control scenarios internationally.