Feral animals in Australia

Australian Government action

The Australian Government works with the states and territories to develop strategies, undertake research and fund key management activities. Under the Environment Protection and Biodiversity Conservation Act 1999, a number of feral animals are recognised as threats to native animals and plants. The impacts of some feral animals have been listed as Key threatening processes and a threat abatement plan has or may be developed. Some other animals, such as feral camels, are also the subject of national plans for management as Existing Pest Animal of National Significance, (under the Australian Pest Animal Strategy)

Threat abatement plans

National action plan

Impacts

Australia's native plants and animals adapted to life on an isolated continent over millions of years. Since European settlement they have had to compete with a range of introduced animals for habitat, food and shelter. Some have also had to face new predators. These new pressures have also caused a major impact on our country's soil and waterways and on its native plants and animals.

In Australia, feral animals typically have few natural predators or fatal diseases and some have high reproductive rates. As a result, their populations have not naturally diminished and they can multiply rapidly if conditions are favourable.

Feral animals impact on native species by predation, competition for food and shelter, destroying habitat, and by spreading diseases.

The Rabbit-eared Bandicoot or Bilby needs a constant supply of carbohydrate-rich seeds and roots. Feral animals such as rabbits graze or degrade vegetation that provides food and shelter for them and other native animals. If vegetation is destroyed or eaten by feral animals, the Bilby and other native species are placed under greater pressure. Feral cats and foxes hunt and kill native birds, mammals, reptiles and insects. It is known that this behaviour threatens the survival of many threatened species.

Feral animals can cause soil erosion. While managed domestic livestock can be removed from degraded areas until these areas are revegetated, it is much more difficult to keep feral animals out of these same areas.

Feral animals can carry the same common diseases as domestic animals. They are a constant source of reinfection for wildlife and livestock, which works against efforts to control costly diseases such as tuberculosis. Feral animals are also potential carriers of other animal diseases (such as rabies and foot and mouth disease) and parasites (such as the screw worm fly). So far, these do not occur in Australia. An outbreak among Australia's wildlife would have an immediate and widespread effect, and would be disastrous for our environment. In some cases it would also be very difficult to control these diseases and parasites if feral animals carried them.

Control methods

It would be desirable to rid Australia of its worst invasive species, but this is not achievable in most cases.

The objective for managing the majority of established feral animals is to reduce the damage caused by pest species in the most cost-effective manner. This may involve localised eradication, periodic reduction of feral numbers, sustained reduction of feral numbers, removal of the most destructive individuals or exclusion of feral animals from an area. The damage caused by feral animals also needs to be considered in context with other factors, such as land use, climate, weeds and grazing pressure from domestic stock.

There are a number of control methods available for feral animals. These methods include conventional control techniques and biological control. Conventional control methods for feral animals include trapping, baiting, fencing and shooting.

During the implementation of any feral animal control program the guidelines for humane treatment and removal, such as those outlined in the relevant Threat Abatement Plan (see below), should be applied, as well as adhering to animal welfare requirements that apply in each State or Territory. The Australian Government contracted the New South Wales Government to develop model Codes of Practice and Standard Operating Procedures for the humane control of feral animals.

Under the Australian Animal Welfare Strategy, the NSW Department of Primary Industries’ Vertebrate Pest Research Unit, has developed a model for assessing the relative humaneness of pest animal control methods .

Conventional control

Conventional methods of control include fencing, trapping, baiting and shooting. Fencing for wildlife management has a long history in Australia with the introduction of netting fences for rabbit and dingo exclusion over 100 years ago. Fencing to exclude other feral species, such as foxes and cats, is more recent. Fencing to exclude feral animals is only a viable option where the area to be enclosed is relatively small. Fences designed to exclude feral animals are much more costly than conventional stock fences, so it is impractical and nearly impossible to exclude feral animals from large tracts of land. These fences also need continuous inspection and maintenance, which is expensive.

A variety of traps are used for feral animal control. Traps include conventional cage traps, soft-catch traps and yards that may be created around watering holes to catch animals as they come in to drink. The setting of cage and soft-catch traps is labour intensive, as traps must be checked at least once a day, and they often have limited success. Some feral animals are trap shy, which means that the animals are reluctant to enter traps even though they are baited with food. Yard traps are commonly used for catching feral goats for live transport to markets in Australia and overseas.

Baiting of feral animals such as foxes, pigs and rabbits is usually done using the poison known as 1080. 1080 occurs naturally in native pea bushes in Western Australia. Many native herbivores (such as kangaroos, brush-tailed possums and small native ground-dwelling mammals) in Western Australia have evolved with a much higher tolerance to 1080 than feral animals. This allows baiting programs to be carried out more extensively than may be possible in other parts of Australia where the effects of 1080 on non-target species needs to be considered. Where there is the problem of non-target species eating the baits, the common practice is to bury baits designed for foxes and feral pigs, or to dye baits green or black when using them for rabbits. Foxes and feral pigs are more likely to dig baits up, as they often dig for food, where as native carnivores are less likely to take buried baits. The green dye reduces the likelihood of birds picking up baits, as many birds use colour to determine the tastiness of food.

Shooting is also used to control animals, such as feral horses, feral pigs and feral goats. Where the control program must take place in rugged terrain and in vast remote areas, helicopters may be used. Helicopter shooting by trained shooters is the most humane way of reducing the number of feral animals in these areas. It is quick and the animals are not subject to the stresses of mustering, yarding and transportation.

Biological control

Biological control is the control of pests by natural predators, parasites, disease-carrying bacteria or viruses. A noted success was the release of myxomatosis in 1950. In the six months following the release, the virus was believed to have killed more than 90% of feral rabbits as it swept through the temperate zone. Mosquitoes or fleas transmit the myxoma virus, but because mosquitoes and native fleas do not readily inhabit dry areas, the arid zone became a haven for feral rabbits. A lack of mosquitoes in semi-arid regions still inhibits the spread of myxomatosis, but in the temperate regions the virus still affects up to 60% of feral rabbits, despite some rabbits having developed limited resistance to the virus. An arid adapted rabbit flea has now been introduced into Australia to assist with the spread of myxomatosis.

In 1995, rabbit haemorrhagic disease (RHD, also known as rabbit calicivirus disease) established itself in Australia and reduced rabbit numbers, especially in arid areas. Nevertheless, in recent years rabbits have become abundant once again in some areas and rabbits are also developing genetic resistance to this disease. The Australian Government is funding, through the Caring for Our Country 2009-2010 Program, further research into improving the viral strains of RHD to counter the resistance developing in rabbits - www.nrm.gov.au/business-plan/funded/09/competitive/index.html

Stringent tests and controls must be undertaken to ensure that all future biological control agents are effective and will not make the problem worse. An example of biological control gone wrong was the introduction of the cane toad in 1935 to control two insect pests of sugar cane. This biological control effort was a failure as it did not control the insects and the Cane Toad itself became an invasive species. The insects pests were later controlled using insecticides and other more suitable management practices.

Any biological control should be used in conjunction with conventional control techniques to manage the damage caused by feral animals.

See also