The Department of Primary Industries (DPI) has warned of a rapid increase in rabbit numbers across Victoria this summer – and landholders need to act now.
DPI Biosecurity Manager for Established Invasive Animals, John Matthews, said data indicates rabbit numbers are starting to rise from a 15 year low.
“Initial analysis of the 2011 spring program indicates increases in both population and active warrens,” said Mr Matthews.
“Recent high rainfall and strong pasture growth will also improve survival and extend the breeding season.”
DPI rabbit monitoring, at 17 sites on farmland across Victoria since 1998, provides nationally significant data as well as a reliable tool for measuring change in rabbit populations, the behaviour of the rabbit haemorrhagic disease (RHDV) and the effects of conventional rabbit control programs.
“It appears a higher proportion of rabbits have antibodies to the biological control agent RHDV, released in 1995-96,” said Mr Matthews.
“This is evident across all sites with around half the kittens, 70 per cent of young adults and 80 per cent of older adult rabbits moving into the next breeding cycle, having antibodies to RHDV and would likely survive further exposure to the disease.
“There were no major differences in the antibody status of rabbits across a range of rainfall zones, indicating the epidemiology of RHDV was similar in semi-arid and temperate areas of Victoria.”
Moderate to high levels of antibodies were consistently found in young rabbits under 12 months of age over a four-year period, inferring that RHDV persisted in the field and recurred annually.
“On a positive note, a sustained reduction in rabbit populations is occurring where broad scale destruction of rabbit warrens has taken place,” said Mr Matthews.
“In areas where warrens were not destroyed, rabbit numbers are already greater or approaching the levels seen prior to the spread of RHDV from 1995 to 1996.
“RHDV is having little impact on reducing rabbit populations, demonstrating the importance of coordinated warren ripping programs, which deliver immediate and more predictable long-term reductions in rabbit populations.”
Mr Matthews said the information reinforced the need for land managers to take action now.
“Our data shows the best results are achieved when control programs are undertaken when rabbit numbers are low and that optimum period will be with us over the summer period,” he said.
“The most effective landscape scale warren-ripping programs have reduced and maintained populations by 97 per cent of their pre RHDV levels, using heavy earthmoving equipment to rip all warrens within a short time.
“The recipe for success is simple – accurate and timely application of the correct control techniques at a landscape scale, based on warren ripping, provides an immediate and sustainable solution for managing rabbit populations.
“Well planned and implemented ripping programs are very successful in reducing and maintaining rabbit numbers at low level for up to 12 years.”
Recent studies show that for a number of critical vegetation communities like buloke or callitris pine, rabbits need to be managed to extremely low levels of much less than one rabbit per hectare to allow for any regeneration and recruitment to occur.
Mr Matthews said DPI would continue to monitor statewide rabbit populations and continue to support community rabbit control programs on priority catchment assets by enforcing action on rabbit control.
All land owners are legally required to control rabbits on their property under the Catchment and Land Protection Act 1994.