Modelling the cost-effectiveness of wallaby control in New Zealand

Bennett?s wallaby (Macropus rufogriseus rugogriseus) was introduced to South Canterbury in New Zealand?s South Island in 1874. The species rapidly established populations throughout the region, and by the 1940s had increased to levels where it had become a significant agricultural pest. Potential wallaby-control techniques include the use of shooting teams with dogs and deployment of 1080 either from the air or as gel applied to foliage. For livestock graziers, shooting teams are probably the least cost-effective of these techniques (i.e. highest cost per unit reduction in average wallaby density), but are preferred to either form of 1080 poisoning because the latter require stock to be withheld from treated areas. In this study, we combine a simple model of wallaby population dynamics with empirically derived estimates of the density-dependent variation in wallaby-control costs to contrast the relative cost-effectiveness of these control techniques. Variation in wallaby density was predicted from a logistic population model modified for the positive effects of rainfall on rates of change in wallaby abundance. The model was fitted to estimates of density- and rainfall-dependent variation in the instantaneous rate of change in wallaby abundance (r), derived from catch?effort data recorded by shooting teams. Comparison of the control techniques demonstrated that the cost-effectiveness of hunting with dogs was lower than that achieved by either poisoning technique, and increased exponentially as progressively lower wallaby densities were targeted. This increase reflected the higher variable cost of locating wallabies to shoot as their density declined. In contrast, because 1080 poisoning is dominated by the fixed costs of bait or gel deployment, overall costs increased linearly as lower wallaby densities were targeted, and the frequency of poisoning was increased. Of the two 1080 poisoning methods considered, deployment using gel applied to foliage was always more cost effective than aerial distribution of bait.

Author David Choquenot and Bruce Warburton
Date 12/04/2006
Year 2006
Secondary title Wildlife Research
Volume 33
Number 2
Institution Landcare Research
Pages 77-83
Notes Notes
Region NZ