Abstract
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.
Highlights
Invasive small mammal pests pose major threats to conservation and production values globally, but are typically expensive to control or eliminate at large scales
It was introduced from Australia to New Zealand over 160 years ago to establish a fur trade, and has become a major pest, causing extensive damage to conservation values, agricultural crops and forest plantations, and by spreading bovine tuberculosis [1]
Topography and density of vegetation, very large reductions in possums and rat densities could be achievable at similar cost to conventional aerial 1080 baiting, and at lower cost compared with conventional ground based poison baiting
Summary
Invasive small mammal pests pose major threats to conservation and production values globally, but are typically expensive to control or eliminate at large scales. In New Zealand, two major pests, the Australian brushtail possum (Trichosurus vulpecula) and the ship or black rat (Rattus rattus) are controlled by poisoning over millions of hectares. It was introduced from Australia to New Zealand over 160 years ago to establish a fur trade, and has become a major pest, causing extensive damage to conservation values, agricultural crops and forest plantations, and by spreading bovine tuberculosis [1]. Such operations are often designed to target the three species of introduced rats, R. rattus which has major impacts on native fauna [3]
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