Cyanide induced aversions in the possum (Trichosurus vulpecula): effect of route of administration, dose, and formulation.

Possums (Trichosurus vulpecula) are New Zealand's main vertebrate pest. Control practices using poisons are likely to remain the most cost effective methods for the immediate future but poisons may be avoided in the field. A series of experiments were conducted to determine whether cyanide bait avoidance involved conditioned food aversions (CFA) induced by sublethal cyanide ingestion. Food aversions were conditioned in three experiments using intraperitoneal or oral routes of administration with three different cyanide formulations over a range of doses. Across all experiments there was a direct relationship between dose and the proportion of animals developing CFAs. When administered orally, doses greater than 5 mg/kg resulted in more than 50% of surviving animals developing aversions. Route of administration or formulation appeared to have no differential effect on development of CFA. Although there was considerable variation between individuals in the degree of aversion shown this may be one mechanism that could account for poor possum kill rates in some poisoning operations.