Looking for something?Close
Hattah-Kulkyne National Park was declared in 1980 and is a highly rabbit-prone environment. Before the arrival of rabbit haemorrhagic disease virus (RHDV), conventional control had reduced rabbit abundance to between two and eight rabbits per spotlight kilometre. After RHDV became established in 1996, spotlight counts dropped to fewer than one rabbit per kilometre. In areas where warrens were ripped, spotlight counts remained below 0.5 rabbits per kilometre.
This low level of rabbit abundance triggered a regeneration response from buloke (Allocasuarina leuhmannii)1 — the first regeneration of this plant species recorded for at least 50 years. After 2004, the rabbit population recovered and a project was set up to demonstrate the most effective combination of conventional control techniques to protect regenerating native vegetation (Figure 1).
To compare the effectiveness of two rabbit control strategies — one involving 1080 baiting followed by warren ripping and fumigation, and the other strategy using only ripping and fumigation.
The project was a partnership between Parks Victoria, the Invasive Animals Cooperative Research Centre, the Victorian Department of Primary Industries and specialised contractors including Daryl Walters (Mallee Land Management Services), Jack Pryse (ripping contractor), Les Lidden (fumigation contractor) and Frann Sette (Sunrise 21 GIS services). Funding was provided by an Australian Government Caring for our Country grant.
Parks Victoria set up a demonstration site within the Hattah-Kulkyne National Park (see map at right). The site is an area of mixed pine-buloke woodland and riverine (black box) woodland within the Kramen management unit of the park. The western portion of the trial area (993 ha) contained six 50 ha treatment blocks. Two treatments were randomly allocated to the blocks and the areas surrounding each block. The two treatments were: 1) poison bait + rip + fumigate and 2) rip + fumigate. The eastern portion of the trial area (422 ha) was the experimental control area with no rabbit treatments applied. Three 50 ha blocks were set up in the control area for monitoring purposes. Outcomes were measured in terms of density of active warren entrances and spotlight counts.
The site generally had high levels of rabbit activity before treatment, as there had been no rabbit control works in the area for the previous five years. Warrens across the entire area were mapped before ripping and spotlight counts were completed. Other details recorded were: the total number of warren entrances, the number of active entrances and the situation of the warren (eg near tree, under log, in open area). Ongoing monitoring was done using spotlight counts and sampling of a subset of known warrens: 30 within each of the nine 50 ha blocks. The no-treatment site was only maintained for six months, after which time it was treated as part of the overall park control program.
Three of the six treatment blocks were poison baited over a two-week period during May 2009. Oat baits containing 1080 were used for poisoning rabbits after a round of three ‘free feeds’ (oats with no poison) had been laid at three-day intervals. Sterile oats were used to avoid residues germinating in the park and were dyed green to minimise bait take by non-target animals. Oats were laid during the afternoon, again to reduce non-target impacts, at a rate of 4 kg/km. A total of 60 km of bait trail was laid at a rate of about 20 linear km/100 ha. Trails were carefully placed in rabbit feeding areas and around warrens to ensure rabbits easily found baits. Dead rabbits were collected from the trail on the first and second mornings after poison baiting. On the third day, bait trails were covered with soil using a quadbike with a small sled attached.
A contractor ripped warrens in all the treatment blocks and immediate surrounds over two weeks in late June 20092. Two 140-horsepower log skidders were used; each with four rear-mounted tines 600 mm in length to ensure that ripping was deep enough to destroy each warren. The tines were modified at the tip with a ‘winged keel’ design that improved the lateral extent of the rip and aided manoeuvring (Figure 2). After each warren was cross-ripped using a zigzag pattern, the front blade on the skidder was used to smooth the ground surface.
The contractor recorded the location of each ripped warren using a GPS and the waypoints were downloaded at the end of the day. A single observer (or ‘spotter’) on a motorbike accompanied the contractor, searching for and marking warrens to be ripped. Any warrens that were inaccessible for ripping, or that were re-opened after ripping, were fumigated using chloropicrin gas in a pressure fumigator. A contractor was hired to carry out fumigation over six days in July 2009. The contractor’s dogs flushed rabbits into warrens and located rabbits in nearby fallen logs. A total of 326 warrens were located and fumigated2. Subsequent monitoring showed a high level of re-openings in Block 5 of the treatment area. This area was refumigated two weeks later and a further 16 warrens were treated.
Best-practice rabbit control involves a strategic approach using multiple techniques to effectively reduce rabbit populations and their impacts.
Key features of the project included training opportunities for staff onsite, and collection of detailed information to estimate comparative cost effectiveness of rabbit control strategies. A field day was also organised to demonstrate the effectiveness of integrated rabbit control to community and other interest groups.
Technical issues that were overcome included:
Overall, each strategy resulted in a major reduction in the rabbit population (Figure 3), and met the park’s management goal of 0.5 rabbits per hectare to allow plant regeneration (Figure 4).
Specific results from the study include:
Recent rainfall meant that soil moisture conditions were not ideal for warren ripping2.
Best-practice rabbit control involves a strategic approach using multiple techniques to effectively reduce rabbit populations and their impact on vegetation over the long term. Parks Victoria is now managing the time between rounds of treatments such that rabbit populations can be maintained below the threshold at which damage occurs. Including poisoning in the treatment regime (ie poison + rip + fumigate, rather than just rip + fumigate) means a longer time can pass before subsequent treatment rounds are needed. Poisoning with 1080 adds significant cost to initial rabbit control but is likely to be cost effective in the longer term. This approach provides a good basis for the development of a feasible, effective rabbit control program for the Hattah-Kulkyne National Park and may also be applicable to other areas.
Table 1. Costs of rabbit control
Thanks to Peter Sandell (Parks Victoria) and Brian Cooke (IA CRC) for providing information for this case study.
Pestsmart Toolkit for European rabbits
Invasive Animals Ltd has taken care to validate the accuracy of the information at the date of publication [September 2011]. This information has been prepared with care but it is provided “as is”, without warranty of any kind, to the extent permitted by law.