Refining operational practice for controlling introduced European rabbits on agricultural lands in New Zealand

Abstract

European rabbits (Oryctolagus cuniculus) pose a major threat to agricultural production and conservation values in several countries. In New Zealand, population control via poisoning is a frontline method for limiting rabbit damage, with large areas commonly treated using the metabolic toxin sodium fluoroacetate ('1080') delivered in bait via aerial dispersal. However, this method is expensive and the high application rates of the active ingredient cause public antipathy towards it. To guide reductions in cost and toxin usage, we evaluated the economics and efficacy of rabbit control using an experimental approach of sowing 1080-bait in strips instead of the commonly-used broadcast sowing method (i.e. complete coverage). Over a 4-year period we studied aerial delivery of 0.02%1080 on diced carrot bait over ∼3500 ha of rabbit-prone land in the North and South islands. In each case, experimental sowing via strip patterns using 10-15 kg of bait per hectare was compared with the current best practice of aerial broadcast sowing at 30-35 kg/ha. Operational kill rates exceeded 87% in all but one case and averaged 93-94% across a total of 19 treatment replicates under comparable conditions; there was no statistical difference in overall efficacy observed between the two sowing methods. We project that strip-sowing could reduce by two thirds the amount of active 1080 applied per hectare in aerial control operations against rabbits, both reducing the non-target poisoning risk and promoting cost savings to farming operations. These results indicate that, similarly to the recently-highlighted benefits of adopting strip-sowing for poison control of introduced brushtail possums (Trichosurus vulpecula) in New Zealand, aerial strip-sowing of toxic bait could also be considered a best practice method for rabbit control in pest control policy.