The Department of Primary Industries (DPI) says data from 17 sites across the state, monitored since 1998, shows numbers at a 15-year high, partly due to resistance to the Rabbit Haemorrhagic Disease Virus (RHDV).

Rabbit populations and the number of active warrens increased during spring.

Favourable seasonal conditions also contributed to the population explosion, encouraging rabbits to do what they are most famous for and extending the breeding season into summer.

DPI biosecurity manager for established invasive animals, John Matthews, said resistance to RHDV was contributing to a higher survival rate.

“It appears a higher proportion of rabbits have antibodies to the biological control agent RHDV, released in 1995-96,” Mr Matthews said.

He said about half of the kittens, 70 per cent of young adults and 80 per cent of older adult rabbits had antibodies that would probably allow them to survive further exposure to the disease.

He said antibody levels were similar across all 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, indicating that RHDV persisted in the field and recurred annually.

Mr Matthews said large- scale destruction of warrens had proved the most effective way to control rabbits.

“A sustained reduction in rabbit populations is occurring where broad scale destruction of rabbit warrens has taken place,” he said.

“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 co-ordinated warren ripping programs.”

Mr Matthews said large-scale ripping of warrens within a short period had reduced populations to their pre-RHDV levels.

shynes@standard.fairfax .com.au