But even in this context, where the target is an introduced pest animal, the debilitating nature of the ensuing diseases, public fears about the nature of such organisms and the potential risks to native animals means that the use of such methods to control the brushtail possum is unlikely to gain wide public acceptance. In Australia, problem populations of marsupials cannot be regarded as pests, but must be treated as desirable species requiring careful and humane management. Developing a safe means of bringing about a managed drop in population fertility would appear to be the ideal way to achieve this goal. There are significant drawbacks, however. Surgery can be traumatic to the animal and is expensive and labour-intensive.
Sterility is permanent.
For reasons of efficiency, males tend to be targeted, and virtually all males must be sterilised to make an impact on population growth. Despite these limitations, however, the technique is being applied to populations like the introduced koalas on Kangaroo Island. Research has shown that reducing male dominance behaviour in populations where this is prevalent can lead to an increase in productivity because dominant males lose the ability to suppress the breeding of subordinates. The Marsupial CRC has a small program investigating the potential of natural plant oestrogens for fertility control in captive populations. Immunocontraception Immunocontraception as a means to control fertility in free-ranging wild animals has gathered a growing number of advocates in recent decades.