Rabbits are considered the biggest feral problem in Australia
(in economic terms), estimated to cause about $200 million damage a
year. Their prodigious breeding rate, as well as their
ability to adapt successfully to most Australian habitats, means
that a single pair can increase in 18 months to 184
individuals. From an initial release of 24 wild rabbits in
1859, the population had increased to an estimated 10 billion by
1926, and rabbits were then such a serious problem that many farms
were abandoned.
The release in 1950 of the myxomatosis virus had immediate and
dramatic effect, killing 99.8% of rabbits. However, over time
there has developed a cycle of rabbits adapting to this virus and
developing resistance. The result has been that, while myxomatosis
is still considered a valuable control tool with an important role
to play in keeping rabbit numbers down, by the early 1990s it was
not enough to reduce the populations to tolerable levels.
The release of rabbit haemorrhagic disease (RHD) in 1996-98 once
again reduced populations by more than 50% in the arid areas of
Australia. This virus has been shown over time to have a patchy
distribution, affecting rabbits living in cooler, more humid
habitats less frequently and lethally. Again, although it
kills tens of millions of rabbits annually, we are still
seeing a situation where rabbits are considered a significant
problem. A study in 2004 found that rabbits are responsible
for an estimated $113 million annually in economic losses
alone.
Specific biodiversity impact information:
- In September 2007, on over 25% of 220
sites with remnant native vegetation in farmlands across
south-eastern Australia (including Tasmania) rabbits were found to
have a sharp impact on tree and shrub seedlings.
- In those sites, common species of trees
and shrubs are not able to regenerate normally and natural
biodiversity will decline as older trees die.
- Rabbits have been increasing steadily
in the last 3 years after being held low by RHD since
1995.
- Many of the young trees that became
established while RHD was at its peak are now being wiped
out.
- Tests on rabbits show that in drier
parts of Australia genetic resistance to RHD is
developing.
- If action is not taken, we can expect
even greater biodiversity loss.
- Low rabbit numbers following RHD have
provided a natural experiment showing that if rabbits are kept
below 1 – 2/ha many native trees and shrubs regenerate
readily.
- It is important to continue methods
such as rabbit poisoning and warren ripping to protect natural
regeneration and seedlings planted by community groups.
- In the longer term we must get the most out of biological
control agents such as myxoma virus and RHD virus, and continue
looking for new agents.
- With climate change and carbon
sequestration firmly on the agenda we should be maximizing tree and
shrub recruitment, not allowing rabbits and other herbivores to
reduce gains.
Ongoing vigilance is therefore required by land managers to rip
and/or fumigate warrens, bait, and to reintroduce RHD where
necessary.
What are we doing?
The IA CRC is working to understand the reasons
behind regional variation in
resistance to the disease and then improve the
effectiveness of RHD. We aim to deliver a freeze-dried
RHD virus product that makes it much simpler to reintroduce
the virus.
We are also trialling a new warren fumigator, using carbon
monoxide, which contains fewer irritants than traditional
methods.
The CRC supports and has membership of the newly-formed Rabbit
Management Advisory Group (RMAG). RMAG is also supported by
Australian Wool Innovations Limited, Meat and Livestock
Australia. Chaired by Broken Hill district wool producer
David Lord, the group includes wider representation from industry,
federal, state and local government and non-government
organisations. The group's objective is to maximise the
benefits of new research and development and advocate newly
developed rabbit control technologies. <more>
