Australian Rabbits

Image result for rabbit australiaThe European rabbit, Oryctolagus cuniculus was first introduced to Australia in 1788 by the First Fleet for food. They remained in a small population for many years, but due to introduction of feral rabbits, a newspaper in Tasmania in 1827 noted that the “common rabbit is becoming… numerous throughout the colony, that they are running about on some large estates by thousands.”

Artificial warrens were used in some areas, such as near Sydney to grow rabbits for their meat, surrounded by a stone wall to prevent- or try to prevent- their escape. Rabbit-theft was common in the 1840’s.

Alexander Buchanan released numerous rabbits into the wild in 1857 for recreational hunting purposes of white settlers into Australia, in South Australia. The number in the wild was fairly constant due to carnivore presence until 1866, but suddenly rocketed upwards due to a decline in predators and the emergence of hardier breeds.

Thomas Austin also released a population of 24 rabbits into the wild in 1859. He had asked his English nephew for 12 rabbits, 5 hares and 22 partridges so that he could continue hunting on Australia. Austin received fewer rabbits so ordered in some domestic rabbits. It is thought that the interbreeding of domestic and wild rabbits contributed to the resilience of the exploding population. Those who released rabbits thought they could do little harm to the environment.

Australia has ideal conditions for rabbits:

  • Mild winters allow year-long breeding
  • Areas cleared for farming which were otherwise forests made large areas of ideal grassland habitat
  • There were a lack of diseases that would target rabbits.

By 1920 some estimates put the number of rabbits in Australia as high as 10 billion, although this is likely to be a high estimate. There are now estimated to be a total of over 200 million Australian rabbits, found throughout the country.

Various methods have been introduced to try to remove or even just reduce the huge rabbit population. Initial attempts of conventional methods such as shooting individuals and destroying warrens have had limited success.

Positive Impacts

The positive impacts of the Australian rabbits are highly limited. By 1869, so many had escaped or been introduced that two million could be caught and killed every year with no significant impact on their population just 10 years after introduction, which provided a constant food source, and allowed enough hunting to prevent other, additional species being introduced. During the collapse of the stock market in 1930, and during the world wars, the rabbits helped provide food and income to Australians, and helped to pay off debts.

Negative Impacts

12-16 rabbits can consume as much as a grown sheep, which demonstrates the huge demands their massive population can put on the environment, when the size of sheep fields are considered. In Hattah-Kulkyne National Park, a population of just 0.6 rabbits per hectare managed to kill all of the Buloke plant saplings.

  • They are considered the most significant factor in the loss of endemic species
  • Compete for resources with native species
  • Have contributed to the decline of the greater bilby, yellow footed rock-wallaby, southern and northern hairy-nosed wombats, the malleefowl and the plains-wanderer.
  • Many Australian plants will only reproduce after extreme weather, meaning that their breeding seasons are very rare and valuable. Rabbits consuming young plants mean that these species may not get to reproduce for decades.
  • Rabbits tend to favour newly growing plants over grown ones, meaning that young plants do not have a chance to reproduce before they are eaten. This makes them a threat to afforestation techniques to help reduce flooding, soil erosion and many other risks.
  • Compete with livestock for pasture
  • Eat crops- leading to the building of the Western Australian rabbit-proof fence to prevent damage to local farms.
  • Australian rabbits cause $113 million per years lost in production and control costs.
  • They often kill young trees by chewing off sections of bark completely around the trees, or even just eating the entire plant.
  • Native plants are not available for horticultural and agricultural work.
  • They eat native plants, laving top soil exposed. This has lead to an increase in erosion as the land is now vulnerable to sheet, gully and wind erosion.
  • It may take 100s of years to restore prior soil conditions. Their soil impact is significant enough to be noted on official government legislation.
  • Local water systems are effected, with increased run off, and increased siltation and bank erosion. This increases local water treatment costs in many areas, as well as natural ecosystems.
  • Dust from wind erosion can reduce air quality.
  • The presence of rabbits encouraged the growth of populations of other invasive species, such as cats and foxes. This increases the effects of predation upon other native animals.

More detail can be read here on precise impacts onto the ecosystem: http://www.rabbitfreeaustralia.com.au/rabbits/impacts/

Control Measures

By 1887, the New South Wales government had offered a £25,000 reward for “any method of success not previously known in the Colony for the effectual extermination of rabbits” due to losses from rabbit-caused damage. 1456 suggestions were received. A royal commission investigated the situation in 1901.

Shooting

This is a very common method for control of small populations. It also provides earnings on the small scale for individuals. However, it does not work on vast populations effectively.

Warren destruction/attacks

Destroying warrens through ripping, where rabbits are buried by a bulldozer working over their warren is another common technique, as are by ploughing, blasting and fumigating. Sandy soils through much of Australia mean that ripping and ploughing are both fairly effective.

A poison may be introduced into the warren or into the surrounding area, so that the animals are killed off by the toxin.

Ferret hunting is a fairly simple technique, where trained ferrets are  introduced into the warren and are made to chase rabbits out to be shot or caught. The capacity for this is limited, due to the ferret numbers being capped by training requirements and each ferret’s stamina, but in conjunction with other techniques, it can be useful.

Historically, traps were placed near tunnel entrances. However, steel leg-holding traps were banned in much of Australia on the grounds of animal cruelty in the 1980’s.

Myxomatosis

Myxomatosis is often shortened to myxo or myxy, and is a virus caused by the myxoma virus among rabbits, and was introduced to Australia in 1950 to help suppress the growth of the rabbit population. The disease causes skin tumours, blindness, fatigue and fever, and eventually, usually, death within 14 days of contraction. It can be spread by the bites of insects such as fleas, where it does not replicate, but is instead passed along by further later bites while it is in a latent condition.

Cottontail rabbits gained only localised skin tumours whilst the European rabbit will more normally gain large lumps around its head and genitals. This can progress to conjunctivitis and sometimes blindness. They become fatigues, lose their appetite, and start to develop a fever. Secondary bacterial infections are common. Death can occur within just 48 hours.

The virus was first field tested for population control in 1938, and was released in 1950. Initially, the rabbits would die typically within just 4 days, which gave little time for the spread of the virus. A more virulent form soon became prevalent, which spread more effectively because it had a lower potency. It reduced the estimated population from 600 million to 100 million in just two years. However, the remaining rabbits were those least affected by the disease; genetic resistance started to develop very quickly, with partial immunity developing in just two decreased. Resistance has continued increasing since the 1970’s, and now kills about 35% of infected rabbits. A second virus was introduced (rabbit calicivirus) in 1996 to further reduce the population.

Rabbit Calicivirus

In 1991m Czach CAPM 351RHDV, a strain of rabbit calicivirus causing rabbit haemorrhagic disease (RHD), was imported to Australi under quarantine to see if it could be used as a biological agent against the New Zealander and Australian rabbit populations. Testing was performed on Wardang Island in Spencer Gulf, off the coast of Yorke Peninsula, South Australia. In 1995, the virus escaped and killed 10 million rabbits within 8 weeks of its release.

RHD typically only effects adults, with individuals younger than 8 weeks being highly resistant. Victims will tend to die within 36 hours. RHD typically causes rapid blood clot foramtion in major organs. Even those which do not die are typically highly effected, and symptoms can include any of the following:

  • Fever
  • Squealing
  • Coma
  • Uneasiness
  • Anorexia
  • Swollen eyelids
  • Ocular (eye-based) haemorrhages
  • Paralysis
  • Loss of skin
  • Bloody nasal discharges
  • Severe jaundice
  • Lethargy
  • Major weight loss
  • Diarrhoea
  • Constipation
  • Cramping

Within New Zealand the initial attempts to use it in a culling program included a series of cases where farmers would include animals known to be infected into their processing. It was introduced 2 weeks after the breeding season, so all the individuals who survived being born that year survived the virus, showing the need for careful planning of biological techniques.

The virus is generally passed due to other animals picking up the virus and it remaining dormant within their bodies until they pass it out as faeces. Excreted viruses can then infect the rabbits. Fleas and mosquitoes can also spread the virus.

 

Rabbit-proof fence

Image result for rabbit proof fence australiaConstruction started in 1901 by private constructors, but the project to build a fence to prevent rabbit entry was passed over to the government in 1904. The rabbit-proof fence was built across Western Australia in 1907. It was, at the time, the longest unbroken fence in the world, at 1,833 km long.  There are now 3 fences. No 1 crosses Western Australia from north to south, No 2 is further to the west while No 3 runs east to west, so that all three together now make 3, 256 km worth of fencing. The cost was $250 per km length, in total costing $814,000.

It was designed to reduce the passage of foxes and dingoes too, neither of which are native species. Originally wood was used, but termites started to eat through it so it had to be replaces with unattractive woods for termites (pine, mulga, tea tree or wodjil), or with steel.

(Image Sources: http://www.rabbitfreeaustralia.com.au/rabbits/the-rabbit-problem/

http://slwa.wa.gov.au/wepon/land/assets/images/000876d.jpg)

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