Evaluating opossum poisoning operations by interference with non-toxic baits

From eight trials made during 1967-69 a technique was developed for estimating the reduction, by poisoning, of opossums (Trichosurus vulpecula) from the extent of interference with non-toxic flour-paste baits. The model assumes that opossums do not, through experience and learning, search for other baits close by.
The trial data showed that contagion, an increase in levels of bait interference from night to night and very high acceptance levels were a consequence of baits having been preferentially placed on open ridges and spaced too closely.
Manipulation of baits on randomly-located lines showed that if baits were spaced 40 yards apart and lines were at least 200 yards apart there was little evidence of contagion.
Procedures are given for using interference levels from poisoned areas and untreated control areas to estimate kills.