Previous Reports of Damage

Early reports on the feeding of possums were based on observations of possums in indigenous forest. They concluded that "opossums are not grass eating animals" (Mason 1958)^*, and that "the opossum is not and will never become an important grassland pest" (Howard 1963). The diet of possums in pastoral districts was first analysed by Gilmore (1965a, 1965b, 1967). He found that "where root crops were grown as winter feed for stock opossums travelled long distances to feed on them" (Gilmore 1965b), and that "clover and grasses were eaten in quantity and by large numbers of opossums throughout the year" (Gilmore 1967). He speculated that "opossums may seriously reduce the carrying capacity of the land" (Gilmore 1965a). Shortly after that, Quinn (1968) reported an instance where the carrying capacity of one farm had been raised by about 1 ewe/hectare following an intensive poison campaign against the possums, but he also stated that this case "was possibly exceptional". About the same time, surveys (consisting of questionnaires supplemented by interviews and inspections) in several agricultural districts (Anon 1966, 1967a, 1967b, 1968) all indicated that possum damage to crops and pasture was of minor importance. This is illustrated by two quotations: "crops close to forest fringes were damaged to some extent but, taking cropping as a whole, the damage was not significant" (Anon 1967b) and "opossums do eat limited amounts of pasture … but … there is no evidence that they have affected the carrying capacity of the land generally" (Anon 1967b). More recently, Harvie (1973) published the results of stomach analyses of possums collected in 1968 and 1969 from four farms including the one reported on by Quinn (1968). She estimated that pasture formed about 30 percent of the diet of possums sampled while feeding in paddocks, and, using a figure of 43 possums/ha, calculated that the stocking rate could possibly have been increased by 2.5 sheep/ha. (Recalculation of these data indicate an increased stocking rate of 1.3 sheep/ha: Fitzgerald 1977).

From our preliminary investigations, it is evident that serious localised page 199 damage can occur, particularly near forest or scrub margins. The damage to pasture and crops (such as turnips, chou moellier, lucerne) is most noticeable when paddocks are shut-up without stock (e.g. pasture shut up in autumn for winter feed).