Myths and misconceptions about pest animal impact and management
The traditional and commonly held attitude towards pest animals is that if they are present, they are causing significant damage and must be controlled. Whilst it is true that a pest animal will usually have some impact, the issues to be considered are: the extent of this impact; whether there are more significant impacts on the agricultural production or conservation values being protected; and whether it is technically, economically or socially feasible or sensible to do anything about this impact.
Often it is assumed that pest animal impact is directly related to pest animal numbers - that is, the more pest animals, the more impact. The assumption that follows from this is that any reduction in pest numbers will achieve a proportional reduction in impact. However, often this is not the case. For example, rabbits may not compete significantly with grazing stock until pasture availability decreases below a certain point (for example, during summer or drought). Thus controlling rabbits at times of high pasture biomass may not achieve immediate production benefits (although it may enhance the sustainability of production through dry periods).
Controlling populations of feral pigs, foxes or wild dogs may not achieve desired reductions in impact if a few 'rogue' individuals are responsible for most of the damage and these are not removed by the management program.
On the controversial topic of feral cats, whilst diet studies show that they consume many native animals, populations of these species are often stable and it seems that some species can coexist with feral cats in some cases. However, in other areas, management of feral cats may be necessary to ensure the survival of smaller, less stable native animal populations which are more susceptible to local extinction through a range of pressures including predation and chance events such as drought and fire.
Focusing on the impact rather than the pest animal is likely to resolve the above issues. Pest animal research which quantifies impact often finds that it is overestimated and that there are sometimes more significant agricultural or environmental impacts which can be more readily resolved.
Principles and Strategies of Pest Animal Management
Risk assessment model for the Import and Keeping of Exotic Vertebrates in Australia