Operation rabbit removal
Ripping rabbit warrens on his property near Broken Hill has provided not only biodiversity gains but the single biggest boost to the feed base, says David Lord
The chairman of a newly formed rabbit management advisory group, Broken Hill woolgrower David Lord, believes the removal of rabbits from the local landscape has resulted in massive biodiversity gains and lifts in flock productivity.
David manages the family woolgrowing business on ‘Thackaringa’, 40 kilometres west of Broken Hill, and he says that before an extensive rabbit control program in the early 2000s, there were 28,000 rabbit warrens on the property.
"In November 1995, rabbit haemorrhagic disease (RHD) swept through ‘Thackaringa’, killing an estimated 750,000 rabbits, which is roughly equivalent to 75,000 DSE (dry sheep equivalent) of sheep," he says. "We took advantage of the rare opportunity offered to us by RHD, and the availability of some funding under the Natural Heritage Trust, and began a big effort in 2002 to rip the remaining 22,000 warrens, having started ripping in 1988."
By March 2003, David had completed ripping all 28,000 warrens on the property. He says the problem is not unique to his property; anyone with a similar soil type will have similar warren densities. "I’d encourage anyone who feels they can manage it to rip their warrens – it is probably a better business investment than buying land at inflated prices."
David believes that removing the rabbits has provided the single biggest gain in feed base on his country. "Coupled with genetics, what goes into their mouths is one of the most important elements in improving flock productivity," he says.
"Rabbits select the best food – the fresh new shoots and plants – and eat it before you even see it. Production gains don’t necessarily come from increasing the number in the flock. Some of the greatest gains come from increases in wool cut, lambing percentages and body weight. Post-RHD and myxomatosis, rabbits at their very-much-reduced numbers are insidious – unseen but still dangerous – and it’s difficult for some people to understand just what impact they have."
The district has endured 15 continuous years of extreme rainfall deficit and David believes that if rabbits had remained at an elevated level, he might not have been able to retain a nucleus flock of breeding ewes.
"We have not yet seen the true gains of RHD because we haven’t had a good season since its release. But while it is very hard to claim production gains in such a short space of time, we are fairly confident they are there, judging by the condition of the sheep in what can only be described as horrendous seasons.
"One of the amazing things that has been observed on ‘Thackaringa’ since RHD swept through, and the ripping was undertaken, is how little rain is needed to germinate and support native plants. My father John talks about 1949, just before the release of myxomatosis, when over three nights at one water point he caught 20,000 pairs of rabbits – that’s roughly the equivalent of 4000 DSE."
David is one of two woolgrower representatives on the recently formed rabbit management advisory group, which will work with AWI, Meat and Livestock Australia (MLA) and the Invasive Animals Cooperative Research Centre (CRC) (see opposite). Jonathon Tischler from Skipton, Victoria is the other woolgrower.
Ripping the warrens on ‘Thackaringa’ was a slow and exacting process. Every warren location was logged by GPS and stored on computer before the arrival of the bulldozer in the paddock. There was one warren for every 0.47 hectares of land in the major soil type on ‘Thackaringa’. Work was only carried out in the hot, dry summer months when the rabbits were deep underground. David would lead the 250hp dozer, fitted with a five-tyne, 12-foot-wide ripper, using the GPS data already gathered.
"Myxomatosis and RHD have both given us huge production and biodiversity gains," David says. "However, science tells us that they, on their own, are not enough: the scientific evidence of damage at low rabbit densities is irrefutable."
Dr Brian Cooke, program manager for the jointly funded AWI and MLA rabbit-control research program, has ascertained that "with up to two rabbits per hectare there is a reasonable chance of regeneration, at about three rabbits per hectare the chance of regeneration falls off quickly and at about four rabbits per hectare you can kiss goodbye to regeneration of even common shrub and tree species such as Callitris or Casuarina".
Other members of the local Landcare group have also undertaken ripping of warrens and it is now thought that at least 100,000 of the estimated 176,000 in the area have gone.
"Given the very low human population of much of Australia, and the limitations of boundary-to-boundary ripping in some regions, the need for another biological agent would seem to be the answer," David says.
"It is irresponsible for Australians to expect producers to bear the full burden of rabbit control. We don’t have the resources and we aren’t the only ones outside of the metropolitan area using the land.
"Environmental groups need to inform themselves in regard to rabbits and support us because there are huge gains in biodiversity to be had. If the status quo remains, the integrity of the biodiversity of arid and semi-arid Australia will continue to remain at risk, or the alternative is that rabbits can be suppressed further to a point where we can improve biodiversity.
"There are whole suites of trees at risk because they have reached the end of their life and rabbits have prevented the recruitment of new generations. Furthermore, the productivity and longer-term viability of grazing systems based on native pastures will be best when biodiversity is healthy."
More information: David Lord, 08 8091 1638, thackaringa@bigpond.com; Dr Brian Cooke, 02 6201 2032, brian.cooke@canberra.edu.au
Anti-rabbit research
AWI and Meat and Livestock Australia (MLA) have joined forces to fund a number of projects to assess the threat posed by rabbits to Australian livestock producers.
By examining the current status of rabbit haemorrhagic disease (RHD) and rabbit populations, the aim is to place the wool and meat industries in the "best possible strategic position" to minimise the present and future impact of rabbits.
The Invasive Animals Cooperative Research Centre will manage the program. The former CSIRO researcher responsible for managing RHD’s introduction into Australia, Dr Brian Cooke, has been contracted as project manager.
David Lord is chairman of the advisory body representing the industries, which will liaise with Dr Cooke and the research programs.
Find out more about rabbits.
Return to Beyond the Bale Issue 27