Effect of prefeeding, sowing rate and sowing pattern on efficacy of aerial 1080 poisoning of small-mammal pests in New Zealand

Abstract

Context. Aerial poisoning using sodium fluoroacetate (1080) is an important but controversial technique used for large-scale control of brushtail possums (Trichosurus vulpecula) and other pests in New Zealand. The technique reliably produces near total kills of possums and rats, provided that many tens of baits (and therefore many tens of individually lethal doses) are sown for each target animal present.Aim. The aim of this study was to further refine aerial 1080 poisoning by determining the effect of prefeeding, sowing rate, and sowing pattern on effectiveness.Methods. Eighteen experimental treatments comprising all possible combinations of three sowing rates (1, 2, and 5 kg/ha of bait), three frequencies of non-toxic prefeed (0, 1, and 2) and two sowing patterns (parallel and cross-hatched) were applied to each of two forested areas. Treatment effectiveness was assessed from changes in the rate of interference recorded on baited cards for three species: possum, ship rat (Rattus rattus) and mouse (Mus musculus).Key results. Outcomes were highly variable, ranging from increases in pest activity to near total reductions. Possum reductions were highest where one or two prefeeds were used, and at the higher sowing rates (2 or 5 kg/ha), but with some interactions between these factors. For rats, two prefeeds resulted in the highest reductions but sowing rate had no effect. For mice, post-poisoning indices were often high, indicating low effectiveness.Conclusions. Some treatments were highly effective so poor kills were unlikely to have resulted from pests not encountering bait, or the bait being unpalatable. Rather they appeared to reflect sub-lethal poisoning either as a result of low acceptance (as a result of a lack of familiarity and/or satiation) or bait fragmentation. We infer that for possum and rats prefeeding helps reduce this risk of sub-lethal poisoning not only by increasing familiarity, but also (in conjunction with high sowing rates) by increasing the bait encounter rate, particularly for possums.Implications. There is scope to further reduce the amount of toxic bait sown and the cost of poisoning, without compromising efficacy, by fine-tuning the balance between prefeeding and sowing rate based on which species are being targeted and, for possums, reducing bait fragmentation.

Field Trial of an Aerially-Distributed Tuberculosis Vaccine in a Low-Density Wildlife Population of Brushtail Possums (Trichosurus vulpecula)

“…In line with those examples of aerial vaccine delivery, our studies first confirmed that aerial delivery of sachet baits containing live BCG was likewise technically feasible, and straightforward given the technological developments that have already taken place for aerial delivery of toxic baits in pest control in New Zealand [15,42]. The desired ultimate outcome from our studies (demonstration of a reduction in TB prevalence in possums by aerial vaccination) appears to have possibly been achieved since the measured M .…”

“…Like the lipid baits, these cereal baits were lured with chocolate powder and anise but were not enclosed in sachets, and were sown using a helicopter-borne broadcast-sowing bucket [42] flown along eighteen 2.6 km-long parallel flight paths spaced 150 m apart, at a rate of 175 baits/ha. For vaccine deployment (September 2011), sachet-held baits were dropped (via delivery chute) from a helicopter flying along the same flight paths at low speed at 25–100 m above ground level.…”

Unexpected consequences of control: competitive vs. predator release in a four-species assemblage of invasive mammals

“…We chose four study locations in mixed podocarp – broadleaved forest in the North Island of New Zealand (Table 1). Two of the four locations, Whirinaki Forest Park (38°43′ S, 176°40′ E) and Mokaihaha Ecological Area (38°11′ S, 176°03′ E), were chosen because they were areas where possum control was to be carried out using aerially applied 1080 poison, creating a possum removal treatment (Nugent et al. 2011).…”

Behaviour-manipulating parasites as adjuncts to vertebrate pest control

“…Ship rat control at forested sites in New Zealand often takes the form of maintenance efforts every year to keep numbers below pre-determined levels (Taylor et al, 2009). Alternatively, it is suggested that more intensive control could be carried out every third year, to prevent seed mast-driven population irruptions from occurring (Nugent et al, 2011). We thus simulate these two regimes with control imposed as a point reduction in population size (across all age classes) in early spring.…”