1080-induced bait aversions in wild possums: influence of bait characteristics and prevalence

Abstract

The current experiment aimed to determine the proportion of wild-caught possums from previously poisoned and non-poisoned populations that developed aversions to 1080 baits. In addition, we aimed to identify the bait characteristics mediating the ongoing aversions. In an initial test, animals from areas previously exposed to a 1080 control-operation avoided 1080 baits (60–80%), whereas few naive animals (0–20%) avoided these baits. The baits comprised a green-dyed, cinnamon-lured cereal loaded with 0.08% 1080. As a result of the exposure to the toxic baits, over 80% of the naive animals subsequently developed aversions to those baits. Sixty-nine of these averse animals were allocated to one of 16 bait-treatment groups in a factorial design balanced for population, sex, age and bodyweight. Each bait was characterised by four factors: (a) presence or absence of 1080, (b) presence or absence of green dye, (c) lure type (cinnamon or orange), and (d) bait type (No. 7 or carrot). The presence or absence of 1080 or green dye did not influence the degree of bait avoidance. Lure type had a significant effect on consumption, with 53% of possums avoiding an orange bait compared with 73% for cinnamon baits. Bait type also had a significant effect on avoidance rates, with carrot baits being avoided by 42% of possums compared with 83% for No. 7 baits. Changing the bait type would appear to hold the greatest promise for overcoming aversions by possums to cereal bait.