Dual 1080 bait switching for killing cereal-bait-shy possums

To help develop new tactics for the local elimination of possums using a fast-acting toxin (1080; sodium fluoroacetate), we tested whether possums that had survived a cereal 1080 baiting could be poisoned with an alternative peanut butter paste (PB paste) bait that differed greatly in appearance, texture, smell, and taste. A two-stage field trial was undertaken in 2018 in three 50−80 ha study blocks in mature pine forest near Rotorua. All three blocks were baited with hand-laid cereal 1080 baits without first pre-feeding with non-toxic cereal bait, and then baited again 49 days later with hand-laid 1080 PB paste. All three blocks were baited (‘pre-fed’) with non-toxic PB paste at some time before toxic PB paste was deployed: one block before the cereal 1080 baiting, one block after, and one block both before and after. The non-pre-fed cereal 1080 baiting killed 72.4% of 134 radio-collared possums. Subsequent trail camera monitoring of freshly deployed non-toxic cereal baits recorded 31 visits by possibly half of the 19 radio-collared possums that had survived the 1080 cereal baiting but did not record any bait consumption by them, indicating likely bait aversion. The PB-paste baiting killed 22 of 24 (92%) radio-collared survivors of the cereal 1080 baiting. The two survivors not killed had not been pre-fed before the cereal 1080 baiting. These results indicate that switching to a different bait type can effectively target survivors of current best practice operations, and hints that pre-feeding with the different bait type may be most effective if it is conducted before the possums are exposed to any form of 1080 bait. The finding provides a new tactic that could help achieve complete local elimination of possums through the novel use of tools that are already available.