Duration of cyanide-induced conditioned food aversions in possums

Learned aversions developed following sublethal ingestion of poisons are reported to be long-lived in many pest species. This study aimed to identify the duration of bait aversions following poisoning with a common poison (cyanide) used for possum control in New Zealand. Groups of possums with bait aversions (following cyanide poisoning) were reexposed to the bait (flavoured food) in a 2-choice test, at intervals of 1, 3, 6, 12, or 24 months. The relative intakes of the bait (used as the measure of bait aversion) did not differ between treatments (0.21, 0.21, 0.27, 0.32, and 0.20) for the 5 groups, respectively. The effect of repeated reexposures to the bait was also tested. The proportion of flavoured food eaten was 0.11, 0.19, 0.23, 0.33, and 0.36 for 1 to 5 reexposures, respectively. There was a significant increase in intake with repeated exposure. Thus, cyanide-induced aversions were strong and lasted for at least 24 months. The aversions weakened over several reexposures to the bait, but only for those individuals that had weaker initial aversions.