Rabbit populations in most of Australia fluctuate mainly in response to variation in rainfall. In the drier rangelands, rabbit numbers increase during favourable seasons and decline during droughts to around 1% of peak numbers. Therefore long-term trends are difficult to identify.
In some higher rainfall areas, rabbit numbers have fallen in recent years because of cropping, warren ripping and property development. Rabbits often remain abundant in habitats where they are difficult to control, such as rocky hills and other refuges.
After the introduction and establishment of the virus causing myxomatosis in the early 1950s, rabbit numbers fell dramatically, and rabbits died out in some marginal habitats.
The impact of the disease was greatest in the semi-arid areas where the carriers (vectors) of the virus, mosquitoes, are seasonally abundant.
The impact was less in those areas where there are few mosquitoes, such as Tasmania, Western Australia and some tableland regions.
The introduction in 1968 of the European rabbit flea (Spilopsyllus cuniculi), an alternative, more perennial vector, resulted in large reductions in rabbit populations in Tasmania, south-western Western Australia, on tablelands, and in parts of South Australia.
The 1993 introduction of an aridadapted Spanish flea (Xenopsylla cunicularis) is intended to cause similar reductions in the drier rangelands, and its spread and efficacy are currently being evaluated.
The efficacy of myxomatosis declined in the 1950s but has remained more or less constant since then and myxomatosis still plays a major role in limiting rabbit numbers. The present density of rabbits in Australia compared to the situation before myxomatosis was introduced is not known.
On average, rabbit numbers are thought to be about 5% of premyxomatosis abundance in the higher rainfall areas and perhaps 25% in the rangelands. Although the resistance of rabbits to the virus has increased, this has probably been balanced by the evolution of more virulent strains of the virus.
The effectiveness of myxomatosis in the long term cannot be predicted, so no reliance should be placed on its continued efficacy.
Development of a strategic management approach:
Colonial governments and their successors relied on stringent legislation requiring landholders to undertake control. Various techniques were used, including shooting, poisoning, fencing, and even the intentional spread of predators such as cats.
Most techniques were relatively ineffective, although with determination and persistence, and using rabbit-proof fences as boundaries, some landholders achieved sustained, low rabbit densities and occasionally complete local eradication.
Most evidence indicates that successful rabbit management requires integrated action at the state, regional and local level. Land managers need a clear understanding of techniques and goals and they need to accept responsibility for the action required.
Extension programs increase general awareness and understanding of the damage rabbits cause and what can be done to alleviate the problem. An essential part of raising public awareness will be well-trained and motivated state and territory workers.
Technical and Further Education Colleges can have an important role in training people in techniques of extension, damage assessment and control.
What is the strategic approach?
The emphasis in these guidelines is not on killing rabbits, but rather on their efficient and strategic management to reduce the damage they cause to production and conservation values in the most cost effective way.
Rabbits are but one factor in a complex and changing agricultural environment that includes a highly variable climate, fluctuating commodity prices, other animal and plant pests, farm stock and the profitability of farming businesses. Farmers need to consider investment in rabbit management in the context of investment in other areas of the farm business unit.
Rabbits also need to be considered in relation to their impact on natural and seminatural ecosystems, and on the biodiversity within them. A strategic approach to the management of rabbits developed in these guidelines is based on four key activities:
Defining the problem:
— The problem should be defined in terms of rabbit damage and the reduction in rabbit density required to reduce or prevent the damage.
Developing a management plan:
— Land managers must establish clear objectives in terms of the desired production or conservation outcome sought. Options for rabbit management include local eradication, strategic management, crisis management and no management.
Eradication will rarely be a feasible goal. These guidelines strongly recommend sustained, strategic management as the principal management option.
Implementing the plan:
— A local or regional approach to rabbit management is usually most effective. This generally requires coordinated action by individual property owners and government and other agencies.
Monitoring and evaluating the program:
— Monitoring has two aspects. Operational monitoring assesses the efficiency of the control operation. Performance monitoring involves gathering information to determine whether the strategy is meeting the desired long-term production or conservation goal.
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