Why 0.02%? A review of the basis for current practice in aerial 1080 baiting for rabbits in New Zealand

Sodium fluoroacetate (1080) has been used as an aerially distributed toxin against mammalian pests in New Zealand since the 1950s. Although its use for rabbit (Oryctolagus cuniculus) control ceased temporarily after the illegal release of rabbit haemorrhagic disease virus (RHDV) in 1997, there has been a recent resurgence in the use of aerial baiting with 1080 to control rabbits as the efficacy of RHDV has fallen. Current practices for rabbit control using 1080 have changed little since the 1980s, with high sowing rates and low toxin loadings commonplace. The lack of ongoing development in baiting practices for rabbit control contrasts sharply with continued improvements in the aerial 1080 baiting practices for brushtail possums (Trichosurus vulpecula) in New Zealand, such as a shift to a comparatively high 1080 loading and using much lower application rates of prefeed and toxic bait. These modifications have resulted in an overall reduction in the amount of toxin used for possum control. The disparity in these two approaches prompted a formal review of the rationale on which the current 1080 baiting practices for rabbits are based. Two issues emerged strongly. First, the current low toxin loading used (0.02–0.04% 1080 in bait) is not based on experimental optimisation in New Zealand but, rather, on research conducted several decades earlier in Australia. Second, despite long-standing concerns about the quality of carrot bait used in New Zealand, current bait manufacturing and distribution practices still produce large numbers of small sublethal fragments. Thus, the current New Zealand practice of multiple prefeeds and very high sowing rates of bait with a low 1080 loading used against rabbits seems to have resulted from the need to compensate for the low toxic loading and poor quality control of the bait (carrots). We, therefore, suggest that there is considerable potential to improve current aerial 1080 baiting practices for controlling rabbits in New Zealand. More generally, these findings also help illustrate that ‘best’ pest-management practice may sometimes be based on pragmatic solutions aimed at overcoming unrecognised internal constraints that are in fact avoidable. Refining and modernising vertebrate pest-control programs, so that they better meet efficacy requirements and contemporary public expectations, therefore requires understanding not just that a solution works, but also how it works.