1080-baits for fox control: Is everything all that it seems?

Abstract

The Red Fox (Vulpes vulpes), wild Dog (Canis lupus familiaris), Rabbit (Oryctolagus cuniculus), and feral Pig (Sus scrofa) can have a significant and profound impact on biodiversity and/ or agricultural production in Australia (Saunders et al. 1995; Williams et al. 1995; Choquenot et al. 1996; Fleming et al. 2001). Baiting programmes with 1080 (sodium fluoroacetate) form an integral and, in some cases, the only means by which the impacts of these invasive species can be managed over a large-scale (Saunders et al. 1995; Williams et al. 1995; Choquenot et al. 1996; Fleming et al. 2001). However, in recent times, there has been growing concern among some Australian rural communities that some 1080 products are not as effective as they once were, particularly those used for baiting foxes. Although such reports are often anecdotal, their increasing frequency is of concern. Recently, the Malleefowl Preservation Group in Western Australia conducted a semi-formal survey of their Newsletter readers regarding the effectiveness of 1080 products against Foxes, wild Dogs, and Rabbits. Over 40 responses were received from 15 different postcode regions with up to 50% of these respondents believing some 1080 products were no longer effective (Malleefowl Preservation Group unpublished data). Similarly, participants in coordinated community 1080-baiting programmes in Victoria surveyed during 2004/05 suggested that poor bait take, loss of efficacy, risk to farm dogs, and the high associated costs were the main reasons for less than ideal control programmes (McPhee 2005). This suggests that questions regarding the effectiveness of 1080 products are not unique to Western Australia. More recently, in NSW, the effectiveness of some 1080-baiting programmes was shown to be less than ideal, even when a coordinated approach was used (Gentle 2007a; Bengsen In Press). In one instance, such a programme with 3 mg 1080 baits reduced fox abundance by only 30% (Bengsen In Press). There are a number of reasons why baiting programmes may have, or are perceived to have failed (see below), including the loss of effectiveness of the active ingredient against the target species. With respect to foxes, the only assessment of their sensitivity to 1080 was a provisional study undertaken in the late 1980s when the sensitivity to 1080 of 11 foxes was determined: 3 from the Australian Capital Territory (ACT) and 8 from Western Australia (WA) (McIlroy and King 1990). The provisional nature of this study precluded a detailed estimate of the sensitivity of these foxes to 1080. Moreover, it is also possible, and probably highly likely, that the sensitivity of Australian foxes to 1080 has changed since the assessment undertaken in the 1980s. This Forum Essay raises some of the possible reasons for any decreased baiting effectiveness, particularly the impact of any decrease in the sensitivity of foxes to 1080. The original data of McIlroy and King (1990) are reworked so as to gain estimates of the Lethal Dose 50 and Lethal Dose 99 values and their associated 95% Confidence Limits. The implications of these findings for pest management and conservation programmes, and some suggestions for future research, are also discussed.