Understanding the biology and behaviour of feral rabbits is a key to their control.
Rabbits generally live underground in warrens, though in some circumstances they can be found sheltering under dense vegetation or debri. In many areas they can get the moisture they need from the plants they eat, but in dry areas they need access to water for survival.
The number of rabbits in a warren is proportional to the number of entrances, so warren size and density can be used to estimate the number of rabbits present. Rabbits may venture up to 400 metres from the warren to graze, but most grazing occurs within 200 metres of their home base.
Rabbits eat mainly low herbs and grasses but also dig for roots and bulbs – and may even climb trees for feed during drought. They deplete palatable plants in pastures in proportion to rabbit density and have a very high ‘search efficiency’ – being able to search out and find the seedlings of preferred species. Their biggest impact on total vegetation biomass is when they are in very high numbers (before a ‘population crash’) and when fighting for survival during times of food scarcity.
They are very territorial with both males (bucks) and females (does) defending their territory aggressively against other rabbits. Home territories are marked by dung piles and urine.
As the saying goes, ‘they breed like rabbits’. When seasonal conditions are sound rabbits can have five or more litters in a year – and can even manage a couple of litters in poor seasons. A breeding unit may include one to three males and over half a dozen females. A dominant male will mate with the more dominant females, while less dominant rabbits are likely to form pairs.
The communal aspect of rabbit behaviour can assist in the transmission of diseases.
Useful references include:
- Lange RT & Graham CR. (1983) ‘Rabbits and the failure of regeneration in Australian arid zone Acacia.’ Aust. J. Ecol. 8:377-381.
- Mutze G. (2015) ‘Barking up the wrong tree? Are livestock or rabbits the greater threat to rangeland biodiversity in southern Australia?’
The number of rabbits and warrens, and their distribution, should be assessed as an initial step in the development of a planned, integrated rabbit control program. Control programs may be instigated at any time funds and resources are available, but full advantage should be taken of any low troughs in rabbit numbers, e.g. due to drought or disease, with conventional control measures used to help forestall any recovery in rabbit numbers. The following notes and links provide information on control options.
Regional NRM bodies and State government agencies around Australia are also available to provide advice and possibly assistance. They may be able to help develop district-wide programs where neighbours work together, across tenures, to control rabbits - possibly coupled with feral cat and fox control as well.
The PestSmart Connect Toolkit (a web-based reference library) has been established through the Invasive Animals Cooperative Research Centre. It presents very useful background information, outlines a four step approach to rabbit action (Assessing the problem, Planning, Control, and Monitoring), and provides guides to help with each step. Other resources include:
• Regional NRM Bodies – see Regional NRM organisations
• Some relevant State agencies & management guides – see Control techniques and best practice
• PestSmart Connect Toolkit - see European rabbit
• Humane control – see What is the most humane way to control wild rabbits
The best way to control rabbits long-term, in most places, is to destroy their warrens and hiding places. This means that they cannot survive the hot summers, and cannot rear their young successfully. Rabbit populations usually take many years to recover from a thorough warren destruction program. Recovery will take even longer if the ripped warrens are regularly checked and follow-up work done when needed.
Successful warren destruction programs rely on working out the extent of the rabbit problem by surveying the area for signs of rabbits, e.g. active rabbit warrens, with holes that are obviously being used, especially the doe’s strenuous hole cleaning just before she gives birth. This leaves a streak of dirt which is often visible for some distance. Other signs are fresh rabbit droppings, and chisel-shaped teeth marks on food plants.
Before taking to the paddock with a tractor and ripper, proper planning can save time and effort. Often warrens in open country can be easily seen in aerial photographs, which can be invaluable to planning a control project. Marking all of the warrens will save a contractor’s valuable time. GPS technology is an invaluable aid to planning the most efficient way to cover all warrens in an area.
Usually the best time of year to destroy rabbit warrens is in the late summer, when rabbit numbers are already low and the soil is dry and will collapse more easily. It is always best to wait until rabbit numbers are already low, or to lower them by other means such as poison bait.
Effective ripping of warrens relies on deep ripping with close ripping lines and the ripping extending past the warren. Ideally, the ripper tines should be to a depth of 900 mm, at a spacing of 500 mm. After ripping one way it should be repeated at 90° — this process is known as cross-ripping.
Particular equipment may be useful for particular jobs. To protect native vegetation, a single ripper tine on a front end loader or a backhoe can do the trick. Blade ploughs may be adequate for light or loamy soils, and disc cultivators may be successful in cultivated areas where rabbit numbers are low.
Ripping warrens in steep or rocky and sheet limestone country can be most difficult, if not impossible. Explosives can be used to destroy warrens which are otherwise inaccessible. The use of explosives is limited, because they are expensive and dangerous.
Fumigation is used if warrens have been re-opened after ripping, or in areas which cannot be ripped. This may be because they are inaccessible, i.e. if they are too steep or rocky, or if they are in particularly sensitive areas such as archaeological sites.
Static fumigation uses tablets which produce phosphine gas when damp. One or two tablets are placed in each hole, which is then filled with soil.
With pressure fumigation, all but one of the holes in a warren are blocked up, and the fumigating gas then introduced in the remaining hole using a special machine which produces smoke to show up the last few holes. Warrens can be fumigated with chloropicrin, or car exhaust gas.
Once again, fumigants must be used carefully, as the chemicals are poisonous to humans as well.
The most commonly used poison to control rabbits is sodium monofluoracetate, commonly known as 1080. 1080 must only be used under the supervision of a qualified operator, and there are different laws controlling its use in each of the states of Australia. For instance, the type of bait you can use with 1080 varies from state to state.
Many native plants, particularly in WA, have naturally high levels of 1080, so some of our native animal and bird species have quite high resistance to 1080.
Another poison is Pindone©, an anticoagulant compound which acts in a similar way to common rat poisons. Pindone© can be used where 1080 cannot be used because of the risk to domestic pets, such as in urban areas, on golf-courses, around farm buildings, and in market gardens. Pindone© also has an effective antidote, which is not the case for 1080.
These poisons are not to be used lightly. If they are used incorrectly, native mammals and birds, livestock, pets and even humans can be at risk. In addition, careless use can lead to the poison being ineffective, particularly through rabbits developing resistance to the poison, or even becoming shy about eating the bait — bait-shyness.
Both the effectiveness and selectivity of poisoning rabbits are enhanced by pre-baiting with non-poisoned bait and ensuring that only rabbits are taking the bait; using bait that is most attractive to rabbits; use minimum concentration of poison sufficient to kill rabbits; placing the bait in the prime feeding areas of the rabbits; and collecting the carcasses of poisoned rabbits to prevent secondary poisoning of non-target species.
Excluding rabbits with netting fences is effective with good fence maintenance, but very expensive. It can be used to prevent re-infestation of high-value areas, eg. horticultural crops, revegetation areas, carbon plantations, or wildlife sanctuaries.
Shooting rabbits is rarely an effective control method by itself. Generally, only about a third of a rabbit population is removed and the rabbits will quickly breed up again. Shooting can be humane with a good shot, but an inhumane method if the shooter is not accurate.
Traps are also ineffective by themselves. Steel jaw traps are banned in most States, as they are inhumane and can catch animals other than rabbits. Cage traps are sometimes used to capture rabbits for research purposes or, in small numbers, subsequent humane disposal.
In their natural environment, in Europe, rabbits are attacked by many pests, diseases and predators. One of the biggest problems with animals introduced to another country is the absence of the biological controls to keep their densities low if they become feral. This is a main reason why introduced species often get out of control in their new environment.
The European fox and cats have also become feral in Australia, however they cause problems of their own amongst native animals and livestock. Many native raptors, such as eagles, now have rabbits as a large part of their diet. Generally, predation may help slow the rate of increase in rabbit numbers but, at modern levels, it has not been sufficient to make much difference in population size.
Some diseases followed the rabbits out here. In addition, two important diseases have been introduced to Australian rabbits; myxomatosis in the early 1950s, and rabbit haemorrhagic disease (RHD), formerly known as rabbit calici-virus disease (RCD), in 1996.
The development of resistance in rabbits to the myxoma virus has lessened the effect of the disease, though myxomatosis still accounts for about 40-60% control of rabbits in many regions of Australia. RHD has been highly successful across the lower-rainfall rangelands of southern Australia with reductions in rabbit numbers in excess of 95%. The virus was not as effective in the higher rainfall areas of Australia. Low level resistance to the RHD virus is now appearing in some regions.
Biological controls, such as RHD and myxomatosis, are very useful, even spectacular at times, but they are not enough by themselves. Land managers should be highly aware of the need to integrate conventional control methods with biological control, especially when rabbit numbers are low, to maximise the benefit of the biological control agents.
The importance of biological agents for rabbit control cannot be over-emphasised. Australia has an on-going need to seek new biological control agents and to promote the vectors which transmit them, especially with the reduced manpower and finances available to control rabbits on properties across much of Australia. The economic and environmental returns from the biological control of rabbits far outweigh the relatively low cost of introducing the agents.
Trials and planning are underway for a form of the RHD virus (RHDV1 K5) to be released in Australia, through the RHD Boost project. Landholders and communities are invited to help by recording current rabbit numbers and by reporting any evidence of diseased rabbits. More information is available at the PestSmart website.