In Australia, rabbits are a serious mammalian pest and are an invasive species. Annually, European rabbits cause millions of dollars of damage to crops.
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Since their introduction from Europe in the 19th century, the effect of rabbits on the ecology of Australia has been devastating. Rabbits are suspected of being the most significant known factor in species loss in Australia. The loss of plant species is unknown at this time. Rabbits often kill young trees in orchards, forests and on properties by ringbarking them.[1]
Rabbits are also responsible for serious erosion problems as they eat native plants, leaving the topsoil exposed and vulnerable to sheet, gully and wind erosion. The removal of this topsoil is devastating to the land as it takes many hundreds of years to regenerate.
Rabbits were first introduced to Australia by the First Fleet in 1788. They were bred as food animals, probably in cages. In the first decades they do not appear to have been numerous, judging from their absence from archaeological collections of early colonial food remains. However, by 1827 in Tasmania a newspaper article noted ‘…the common rabbit is becoming so numerous throughout the colony, that they are running about on some large estates by thousands. We understand, that there are no rabbits whatever in the elder colony' [i.e. New South Wales][2]. This clearly shows that a localised rabbit population explosion was underway in Tasmania in the early 19th century. At the same time in NSW Cunningham noted that '... rabbits are bred around houses, but we have yet no wild ones in enclosures...’ He noted that the scrubby, sandy soil between Sydney and Botany Bay would be ideal for farming rabbits[3]. Enclosures appears to mean more extensive rabbit-farming warrens, rather than cages. The first of these, in Sydney at least, was one built by Alexander Macleay at Elizabeth Bay House,'a preserve or rabbit-warren, surrounded by a substantial stone wall, and well stocked with that choice game'[4]. In the 1840s rabbit-keeping became even more common, with examples of the theft of rabbits from ordinary peoples' houses appearing in court records, and rabbits entering the diet of ordinary people.
A question remains as to why there was no outbreak before the start of the current infestation. The localised Tasmanian rabbit plague was noted, but it would be surprising if there were no escapes from the many warrens and cages that would have been present throughout the area of European settlement in southeastern Australia. It is possible that native predators, particularly carnivorous dasyurids, were much more effective as natural controllers of the population than the later foxes and feral cats. When their populations collapsed as a result of habitat destruction, and sometimes deliberate hunting, rabbit populations could rise with far less restraint.
The current infestation appears to have originated with the release of 12 wild rabbits by Thomas Austin on his property, Barwon Park, near Winchelsea, Victoria, in October 1859 for hunting purposes. While living in England, Austin had been an avid hunter, regularly dedicating his weekends to rabbit shooting. Upon arriving in Australia, which had no native rabbit population, Austin asked his nephew William Austin in England to send him 12 grey rabbits, five hares, 72 partridges and some sparrows so that he could continue his hobby in Australia by creating a local population of the species. However William could not source enough grey rabbits to meet his uncle's order. So he topped it up by buying domestic rabbits. One theory as to why the Barwon park rabbits adapted so well to Australia is that the hybrid rabbits that resulted from the interbreeding of the two distinct types were particularly hardy and vigorous. Many other farms released their rabbits into the wild after Austin. At the time he had stated, "The introduction of a few rabbits could do little harm and might provide a touch of home, in addition to a spot of hunting."[5]
Rabbits are extremely prolific creatures, and spread rapidly across the southern parts of the country. Australia had ideal conditions for a rabbit population explosion. With mild winters, rabbits were able to breed the entire year. With widespread farming, areas that may have been scrub or woodlands were instead turned into vast areas with low vegetations, creating ideal habitat for rabbits.
In a classic example of unintended consequences, within ten years of their introduction in 1859, rabbits had become so prevalent that two million could be shot or trapped annually without having any noticeable effect on the population. It was the fastest spread ever recorded of any mammal anywhere in the world. Today rabbits are entrenched in the southern and central areas of the country, with scattered populations in the northern deserts.
Although the rabbit is a notorious pest it proved helpful to many people during the Great Depression and during wartime. Trapping rabbits helped farmers, stockmen and stationhands by providing something to eat, extra income and in some cases helped pay off farming debts. Rabbits were fed to working dogs, and boiled to be fed to the poultry. Later, frozen rabbit carcases were traded locally and exported. Pelts too, were used in the fur trade and are still used in the felt-hat industry.[1]
A Royal Commission was held to investigate the situation in 1901. Once the problem was understood, various control methods were tried to limit or reduce the population of rabbits in Australia. These methods had limited success until the introduction of biological control methods in the latter half of the 20th century.
Shooting rabbits is one of the most common control methods. However, this has little noticeable effect on rabbit populations.
Destroying warrens through ripping (a procedure where rabbits are dismembered or buried alive as a bulldozer dragging sharp tines is driven over their warrens/burrows),[6] ploughing, blasting, and fumigating is widely used especially on large farms (known as 'stations'). The sandy soil in many parts of Australia makes ripping and ploughing a viable method of control, and both tractors and bulldozers are used for this operation.
Poisoning is probably the most widely-used of the conventional techniques, as it requires the least effort. The disadvantage is that the rabbit cannot be used as food for either humans or pets afterward. Two commonly-used poisons for rabbit control are sodium fluoroacetate ("1080") and pindone.[7]
Another technique is hunting using ferrets, where ferrets are deployed to chase the rabbits out to be shot or into nets set over the burrows. Since ferrets are limited in the number of rabbits they can kill, this is more a hunting activity than a serious control method.
Historically, trapping was also frequently used; steel-jawed leg-holding traps were banned in most states in the 1980s on animal cruelty grounds, though trapping continues at a lower level using rubber-jawed traps. All of these techniques are limited to working only in settled areas and are quite labour-intensive.
In 1907, the rabbit-proof fence was built in Western Australia between Cape Keraudren and Esperance to try to control the rabbit population. European rabbits can both jump very high and burrow underground. Even assuming a perfectly intact fence stretching for hundreds of miles, and assuming that farmers or graziers do not leave gates open for livestock or machinery, it was unlikely to be a success.
Releasing rabbit-borne diseases has proven somewhat successful in controlling the population of rabbits in Australia. In 1950, after research carried out by Frank Fenner, Myxomatosis was deliberately released into the rabbit population, causing it to drop from an estimated 600 million[8] to around 100 million. Genetic resistance in the remaining rabbits allowed the population to recover to 200-300 million by 1991.
To combat this trend, Commonwealth Scientific and Industrial Research Organisation (CSIRO) comprehensively tested over three years from June 1991 calicivirus (also known as Rabbit Haemorrhagic Disease or RHD).[9] The virus accidentally escaped from a quarantine compound on Wardang Island, South Australia where field tests were being carried out on the potential of the virus for biological control of wild rabbits, and by late October 1995 it was recorded in rabbits at Yunta and Gum Creek, in north eastern South Australia.[10] By the winter of 1996, the virus was established in Victoria, New South Wales, the Northern Territory and Western Australia. The success of the virus was found to be higher in extreme heat. This was because it appears there is another calicivirus in the colder, wetter areas of Australia, and that this virus was immunising rabbits against the more virulent form.
A legal vaccine exists in Australia for RHD. There is no cure for either Myxomatosis or RHD, and many affected pets are euthanised. In Europe, where rabbits are farmed on a large scale, they are protected against myxomatosis and calicivirus with a genetically modified virus.[11] The vaccine was developed in Spain.