Warning and Disclaimer

So this is just a blog I'm using to upload a bunch of the essays and assessment tasks I wrote for my various uni degrees. Basically I put a lot of effort into some of these and it seems a waste for them to only be read once... so I figured upload them onto the web and see if anyone looks at them.

did ok at most of my essays, some better than others so copy the ideas at your own risk... Given the slow increase in my marks over the years clearly it took me a while to get started. You can probably work out when I wrote each assessment based on the length of the reference list (and there's probably a correlation with the marks I received for that assessment too)

I had a glance over the cover sheets and don't think there's anything stopping me uploading them as I don't think the uni claims ownership over them. You sign off saying that the work has never been submitted before, not that you won't do anything with it later.

That all being said, if you do find these useful for your own uni work... DON'T copy them (not because I care about you copying them) but because you WILL get done for plagarism yourself... Take some of the main points if you want, definitely steal my reference lists, but don't copy text from the essay because you will get done...

So yeah, read on if you're interested, follow up the references... but don't copy if you know what's good for you

Wednesday, July 27, 2011

Control of Rabbits (Oryctolagus cuniculus) in Australia

Tomas Austin introduced rabbits to Australia in 1859 for sport hunting. With assistance from people they had reached the Queensland border by 1886 and rabbits occupied their current range by 1910. By 1880 rabbits were a large enough pest that they were declared illegal and feral cats were introduced to prey on them (Young, 2000). Today Australia’s 200 million rabbits occupy almost all terrestrial environments south of the Tropic of Capricorn with suitable soil (Australian State of the Environment Committee, 2001).

One of the reasons rabbits are such a threatening species is due to their breeding patterns. Female rabbits become sexually mature at three to four months old and can produce a litter comprising of four or five young every month (Department of Environment and Heritage, 2004). This means that if no other factors apply (which is not true) a female rabbit can potentially have 45 offspring within a year of it birth. Theoretically rabbit populations can have a ten-fold increase in six months. Predation, disease and weather conditions can reduce rabbit’s rates of increase but an increase of eight to ten-fold in one breeding season is common (CSIRO, date unknown).

Rabbits were not a native species to England either. Rabbits are indigenous to the plains of Spain and Northern Africa. England’s earliest documented rabbit remains come from the kitchen midden of a castle at Essex and are dated to be from the late twelfth or early thirteenth century. Rabbits from King Henry (the third’s) royal park were given as gifts in 1235 and by 1257 people were complaining about the destruction caused by the rabbits that (inevitably) escaped (Low, 1999). Complaints made about the destructive nature of rabbits date back even longer than that also. Around 50 BC the inhabitants of the Islands of Majorca and Minorca sent a deputation to the Romans asking for new lands to be given to them as they were being driven out of their country by rabbits (CSIRO, date unknown). Around the same time in the Balearic Islands (that are different series of islands to Majorca and Minorca) inhabitants sent a petition to the Roman emperor asking for military aid against pest rabbits (Low, 1999).

Rabbits are more of a problem in grazing areas rather than cropping areas as cultivation disturbs their warrens. Rabbits are considered to be one of the most destructive species in Australia because they compete with native species for food and shelter and can be linked with the decline of many native species, especially small ground dwelling mammals. When native and cultivated areas are overgrazed they lose their plant cover and there is a subsequent increase in erosion and other land management problems (DEH, 2004). Economic damage by wild rabbits (including agricultural production losses and cost of control) is estimated to be approximately $600 million dollars annually (CSIRO, year unknown). There is also accumulated environmental damage that cannot be calculated. Specific examples of how rabbits have affected native animals can be shown with the decline in wombat numbers in the South East of Australia after rabbits moved into the area and the bilby (rabbit eared bandicoot) that in ten years went from common to only found in areas without rabbits.

Complete removal of rabbits from Australia is not possible using the techniques available today. Except for the removal of the Black Striped Mussel from Darwin Marina in 1999 no terrestrial animal has been eradicated from the mainland of Australia (DEH, 2004). The current objective is to reduce damage caused by pest species in the most cost effective manner (Biodiversity Group Environment Australia, 1999), this is why the term rabbit control is used and not rabbit eradication. However the eradication of small newly established populations of rabbits or populations from small islands has been accomplished. An example of this is Cabbage Tree Island where rabbits were eradicated to aid in the protection of the endangered Gould’s Petrel.

The controls on rabbit populations can be divided into natural and human implemented ones. Natural controls on rabbit populations are parasites, climatic conditions and predators. Obviously these natural controls have been unable to keep rabbit numbers down over the years.

The human implemented controls of rabbit numbers are subsequently divided into mechanical, chemical and biological control methods. Mechanical controls are the least effective at reducing rabbit populations on a large scale and are used as a follow up method to the larger scale of biological and chemical controls. Fences can be used to either exclude the rabbits, which is expensive and only possible with regular maintenance or they can be temporary to prevent access to a food source so as to make baits more attractive (Biodiversity Group Environment Australia, 1999). Another problem with fencing is it will also interfere with other species movements.

Shooting is considered a humane way of killing rabbits by the Biodiversity Group of Environment Australia (1999) despite the opposition to the shooting and hunting of animals by many groups. Shooting however is not an effective method for reducing rabbit populations, as it becomes far more difficult when the population is reduced to a low density.

Trapping is a method that is not likely to result in any long-term reduction in rabbit numbers, as it is extremely difficult to conduct a trapping operation on the scale that would be needed to reduce population numbers. The steel-jawed leg-hold traps are still permitted in some areas of Australia, despite the fact they are considered inhume due to the pain and suffering the animal is subjected to. Barrel and soft catch traps are the humane method when trapping is appropriate (Biodiversity Group Environment Australia, 1999).

The most effective mechanical control of rabbit numbers is harbour destruction, although like other mechanical controls this is most effective as a follow up to a chemical or biological control program to prevent rabbit numbers increasing again. “Destroying rabbits without destroying their homes or ‘harbours’ often gives short-term control. In many cases it is little better than a harvesting operation”. The preferred method of harbour destruction is ripping although in some situations where ripping in not possible explosives may be used (CSIRO, date unknown). If rabbits are using surface refugia either in addition to or in place of warrens harbour control is not possible. This is due to the fact that removal of the shrub layer and other possible surface harbours are also habitat for almost all other ground dwelling animal species (Biodiversity Group Environment Australia, 1999). According to the Biodiversity Group of Environment Australia 1999 humaneness of ripping depends on the population density and warren depth. If the entire warren is destroyed by the ripper the rabbit is said to suffer a “humane” death of quick asphyxiation. If the warren is deeper then the ripper’s tines the rabbit will be left to die “less humanely” of slow suffocation or starvation. Dogs are also often used to drive the rabbits into their warren to take shelter before it is destroyed. This reduces the number of rabbits that survive and can therefore reopen warrens.

Chemical control refers to the different methods for poisoning rabbits. Fumigation is performed in two different ways, pressure fumigation and diffusion fumigation. Pressure fumigation seals all burrow entrances and pumps a fumigant mixture of thick smoke, carbon monoxide or carbon dioxide and a poison gas into the warren. This is a slow method only suitable for small areas. Diffusion fumigation places a liquid or pellet that diffuses into the fumigant gas as deep into the warren as possible. Toxins used as fumigants include chloropicrin, carbon monoxide, carbon dioxide, calcium cyanide and phosphine (Biodiversity Group Environment Australia, 1999). The most common toxin used is chloropicrin despite it being seen as less humane then phosphine.

In straight poisoning campaigns there are two methods used, poison baits and the “tarbaby” technique. The most common poison used in Australia is sodium monofluoroacetate, more commonly known as 1080, this poison is also used for fox and feral pig baiting. 1080 occurs naturally in native pea bushes in Western Australia and as a consequence many native species in Western Australia have developed a greater tolerance to this toxin then introduced animals, and this reduces the risk to non-target species in Western Australia (DEH, 2004). The reason 1080 is used is because of its relative cheapness and effectiveness on the target species. It also rapidly degrades in the field and is not cumulative in animals that ingest a sub lethal dose. Its mortality rate is normally in excess of 90% and when combined with a harbour destruction program it normally results in a long lasting control. The disadvantages to 1080 are that there is no antidote, it is highly toxic to livestock and it is soluble in water, meaning that it can leach from the baits in damp environments. However after leaching it is quickly broken down by soil microorganisms.

The other poison commonly used is the anticoagulant pindone. This toxin is less toxic to live stock and domestic animals and there is an available antidote. Pindone however is slow acting and cumulative, this means individuals are more likely to ingest a lethal dose before developing an aversion to the bait, however this can also lead to bioaccumulation of this toxin into higher trophic order predators such as birds of prey. This also increases the time that non-target species are at risk. This toxin is relatively expensive and persists in the environment for up to a year and marsupials are also highly sensitive to it (Biodiversity Group Environment Australia, 1999). Pindone is mainly used in urban areas where there is a risk of accidental poisoning to humans or animal companions is greatest.

Some groups debate the humaneness of poisoning by 1080 and pindone. Pindone is seen as less humane then 1080 as it causes extreme pain when it causes bleeding in the joints. There is apparently little evidence that 1080 causes prolonged suffering. When humans have ingested a sub-lethal dose of 1080 the majority report there being no pain.

The tarbaby technique is more target specific than poison baiting but it is unsuitable to light sandy soils (that rabbits often favour) and 1080 is precluded from this technique due to the concentration required. This means that a less humane toxin like pindone will be required (Biodiversity Group Environment Australia, 1999).

Biological control is the introduction of a living organism to control the population of another organism. It could be the introduction of a predator (in the rabbits case the unsuccessful introduction of cats) or a pathogen (such as myxomatosis or rabbit calicivirus disease (RCD) in the case of rabbits). Biological controls of rabbits are the main method used for controlling numbers. Mechanical and chemical controls are mainly used as follow up campaigns.

Myxomatosis was released in Australia in 1950 and it is believed that more than 95% of rabbits in southern Australia died within six months. Myxomatosis is spread by blood-sucking insect vectors and as a consequence is more prevalent in humid areas then arid areas. Rabbit numbers dropped again in 1969 when the CSIRO introduced the European rabbit flea to be a new vector (Young, 2000). Rabbits are slowly beginning to develop a resistance to this virus however and now the field strain of this virus normally has a mortality rate of 40-90% (Biodiversity Group Environment Australia, 1999).

RCD was first reported in rabbit populations in China in 1984. In 1991 the CSIRO imported the disease and began laboratory tests on its effect on wild rabbits and a host of other non-target species. Field investigation began in March 1995 on Wardang Island and the virus escaped to the mainland in October 1995, probably due to windborne vectors. It was accepted as a biological control by the relevant government bodies in 1996. RCD is believed to be more effective in arid areas than humid ones with a reduction rate of between 65% to >95% (Biodiversity Group Environment Australia, 1999 and CSIRO, date unknown).

More people than those that challenge the other methods have challenged the humanness of these two diseases. This is probably due to the fact that in theory RCD and myxomatosis threaten people’s pet rabbits as well as the wild pest populations. The majority of people opposed to biological control of rabbits seem to be opposed to the perceived threat to their pet animal rather then from an animal rights point of view. As a result of this many of the arguments against these diseases are highly emotive and when combined with inaccurate facts mean that their validity can be questioned. An example of this is an anti-RCD group that claims rabbits with RCD suffer both depression and sadness, a lack of coordination and anorexia. This is despite the fact that rabbits generally die of RCD within 36 hours of gestation.

The humaneness of myxomatosis is a little easier to challenge. This is because the disease can be acute or chronic (as opposed to RCD which currently only has an acute form) and in its chronic form can cause prolonged suffering. Also myxomatosis is a pox disease that has visual effects on the rabbit, while RCD shows no external symptoms. This may lead to more opposition to myxomatosis than RCD, as it “looks” worse.

An important point to note about both RCD and myxomatosis is that like all biological controls humans now no longer have any control over them. These diseases are breaking out in the wild without assistance (although they are regularly spread deliberately). Even if it was decided that our previous decisions about biological control of rabbits were incorrect and that all possible efforts to prevent the disease from spreading should be made humans have no way to stop the spread of this disease. There are vaccinations in existence for both myxomatosis and RCD but for these to take effect in the wild every wild rabbit would need to be caught and inoculated. If it were possible to catch every single wild rabbit there would be no rabbit problem in Australia as every rabbit could be caught and sterilised.

A third form of biological control is immunocontraception. This is a fertility control agent that uses a viral vector (in the case of rabbits a modified version of the myxoma virus). This is a method considered a desirable and humane way to control pest species by animal welfare groups. This method does have it drawbacks however. The main drawback being that it’s only in the experimental phase of development. The other problem is that for this method 60 to 80% of female rabbits would need to be infected to achieve a reduction in rabbit numbers.

Arguments about whether it is ethical to ‘tamper’ with a species ability to reproduce like that can be made. However the question that needs to be asked is if it is an infringement on an individual animals right to be prevented from reproducing surely it is a greater infringement on the animal to kill it outright. Humans will be killing rabbits to control their numbers if there is no alternative so even if immunocontraception is an infringement on rabbit’s rights surely the lesser of two evils (sterilisation compared to death) is the desirable option.

There are commercial interests in the wild rabbit population. Prior to the introduction of myxomatosis there was a substantial wild rabbit harvesting industry but this industry collapsed after the diseases introduction. The current wild rabbit commercial industry uses field shot animals to supply game and pet meat markets and skins mainly used in the felt hat industry. The annual value of wild rabbit products was estimated to be $9 million in 1991-92 with an additional $2.5 million invested in capital equipment. Added to the fact that the commercial use of wild rabbits are too small and localised to aid the conservation movement it becomes clear that the value of the commercial rabbit industry is trivial when compared to the costs of wild rabbits on agriculture and the environment (Biodiversity Group Environment Australia, 1999).

There is also the possibility of impact on non-target species by a rabbit control campaign. There could be direct or indirect impacts. Direct impacts are when the technique used kills other animals than just the rabbits, indirect impacts are were the reduction in rabbit numbers affects another species.

It has been argued that a reduction in rabbit numbers could threaten native species as the rabbits predators (normally foxes and feral cats, which are other pest species in Australia) would have to change there prey species from the abundant rabbit population to threatened native species. However it is advised that if this situation has a possibility of occurring an integrated campaign is conducted targeting not only the rabbits but their predators also (Biodiversity Group Environment Australia, 1999). Also if as is more then likely true one of the main reasons for the species being threatened is that it is being out competed by rabbits the reduction in rabbit numbers may allow that species to re-establish its numbers so it is less susceptible to predator pressure.

Rabbit reduction is already affecting the populations of Australia’s birds of prey. Young rabbits provide 60-90% of the diet of birds of prey around Mildura. Since the introduction of RCD bird of prey populations have been suffering (Low, 1999).

It has been noted that many indigenous people are opposed to any control program that doesn’t make use of the destroyed animals (Rose, 1995 in Biodiversity Group Environment Australia, 1999). This is because they view exotic species having just as much right to inhabit the land as native fauna.

From an animal rights point of view it is hard to find an argument against rabbit control. This is because the rights of the individual rabbit or rabbit species need to be balanced against the rights of all the individuals and collective totals of the other species that are threatened by rabbits. Also the rabbit species is not threatened with extinction by these control measures (no control is that effective) so the protection of the species is not an issue. This leaves the choice between reducing the population of one species or the eventual extinction of many other species. To someone holding the animal welfare viewpoint the lesser of two evils would have to be a reduction to rabbit numbers. That of course only applies is if all species are viewed as equal (as animal welfare activists claim to believe).

The viewpoint that rabbit control is a violation of the individual rabbits rights is slightly more persuasive than a total species right viewpoint. From this viewpoint it comes down to the individual rabbits right not to suffer. This argument works better when applied to certain control methods then others (for example anticoagulant poisons and myxomatosis compared to 1080 poisoning and RCD). Obviously the rabbit has the right not to suffer to a certain extent or there wouldn’t be the desire in people to develop more humane methods of control. If they didn’t have this right the focus would be on developing more effective methods without giving any consideration to rabbits suffering.

This right not to suffer will also become a weaker argument if the CSIRO does achieve it aim of developing a method for immunocontraception of rabbits. Even if the individual rabbit is determined to have a right to reproduce the violation of this right is a lesser violation of its right to live and its right not to suffer. For surely if an individual has the right to reproduce it would have a right to live without suffering that would be even higher valued.

Finally it must be noted that if rabbits are left alone without any methods of population control they will end up on a path to self-destruction. This was shown in 1990-91 along the dingo fence in South Australia. Rabbits ate the ground bare in a strip 200km long and several km wide, subsequently they ended up dying by the thousands of heat stress, starvation and disease (Young, 2000). Surely starvation and heat stress are two ways to die that cause more suffering then many of the methods of control used by humans.

All of the factors mean that although the methods used for rabbit control can be questioned ethically. Rabbit population control is a necessary evil. Care is taken to minimise the suffering of rabbits and a lesser of two evils approach is often taken. Also newer and more humane methods are still being developed, there is no end in sight to this ethical or environmental problem but progress is constantly being made. On an ethical front it comes down to the individual rabbits right not to suffer and die (as there is no threat to the species) compared to the protection to many native species and the $600 million that rabbits cost Australia annually. This is the driving force behind the development of more humane population control methods, the conventional view is the individual rabbits right not to suffer and die is obviously not equal to $600 million and the survival of multiple native species.


Australian State of the Environment Committee, 2001. Australian State of the Environment 2001, Independent Report to the Commonwealth Minister for the Environment and Heritage, CSIRO publishing on behalf of the Department of Environment and Heritage, Canberra

Author Unknown, Myxomatosis of rabbits- Resources (an anti-myxomatosis website) available at http://members.iinet.au/~rabbit/intervet.htm last accessed June 2004

Author Unknown, Rabbit Calicivirus Frequently Asked Questions (an anti-rabbit calicivirus disease website) available at http://members.iinet.au/~rabbit/rcdfaq.htm last accessed June 2004

CSIRO, Date Unknown, Rabbit Control and Rabbit Calicivirus Disease: A field handbook for land managers in Australia. Available at http://csiro.au/communication/rabbits/rcd_book.htm last accessed June 2004

Low, T., 1999, Feral Future: The untold story of Australia’s exotic invaders, Penguin Books, Ringwood

Young, A., 2000, Environmental Change in Australia since 1788, 2nd ed., Oxford University Press, Melbourne

Biodiversity Group Environment Australia, 1999, Threat abatement plan for competition and land degradation by feral rabbits, available at http://deh.gov.au/biodiversity/threatened/tap/rabbits/4.html last accessed June 2004
Department of Environment and Heritage, 2004, Feral Animals in Australia, available at http://deh.gov.au/biodiversity/invasive/ferals/index.html last accessed June 2004

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