Rabbit Control

The best way to control rabbits long-term, in most places, is to destroy their warrens and hiding places. This means that they can not survive the hot summers, and can not rear their young successfully. Rabbit populations usually take many years to recover from a thorough warren destruction program. Recovery will even take 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. Obviously this part of the job is very labour -intensive — rumour has it that children have spent a fair proportion of their summer holidays walking around a paddock with a bundle of stakes and a pocketful of markers. The use an ATV or motorbike would be quicker.   Recent developments in GPS technology are 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 900mm, at a spacing of 500mm. 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

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.

Interestingly, 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 can not 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.

Remember that these are 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.

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. The machine produces smoke which shows up the last few holes. Warrens can be fumigated with chloropicri, or car exhaust gas.

Once again, fumigants must be used carefully, as the chemicals are poisonous to humans as well.

These can be used to destroy warrens which are otherwise inaccessible. The use of explosives is limited, because they are expensive and dangerous.

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.

One major rabbit predator, the European fox, and cats have also become feral in Australia, however, they cause problems of its 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 of the numbers of rabbits, but is not enough in itself to make much difference.

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 calicivirus disease (RCD), in 1996.

Myxomatosis is spread from rabbit to rabbit by a biting insect. In Australia, the myxoma virus was originally, spread by mosquitoes only, which meant that it spread well near permanent water or during wet seasons, provided the weather was warm enough for mosquito activity. In the last three decades, two species of rabbit fleas have been introduced to Australia to help the spread of myxomatosis. These fleas are the European rabbit flea, Spilopsyllus cunicularis, which is effective in areas with annual rainfall down to about 250mm, and the Spanish rabbit flea, Xenopsylla cunicularis, which is useful in lower rainfall areas.

RHD has been highly successful across the lower-rainfall rangelands of southern Australia with reductions in rabbit numbers in excess of 95%.  Benefits from reduced rabbit numbers there has included improved availability of feed for livestock, reduced risk of soil erosion and the appearance of native plant species thought to be extinct in the region.  The virus was not as effective in the higher rainfall areas of Australia.   

Biological controls, such as RHD and myxomatosis, are very useful, even spectacular at times, but they are not enough by themselves. 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.  A similar picture is emerging where low level resistance to the RHD virus is already appearing in some regions.  The importance of biological agents for rabbit control can not be over-emphasised.  Australia has an on-going need to seek new biological control agents, especially with the reduced manpower and finances to apply other rabbit control methods on properties, especially in the rangelands, across much of Australia where rabbits are a problem.  The economic and environmental returns from biological control of rabbits far outweigh the relatively low cost of introducing the agents.

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.

Excluding rabbits with netting fences is very expensive, but can be used to prevent re-infestation of high-value areas, eg. farm or market gardens, a building, a revegetation area or a wildlife sanctuary.

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 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.