Introduced Species Which Have Caused Problems
Invasive species are a problem for all countries and Australia is no exception. Despite being an 'island' in a sense, a number of mammal and bird species have been introduced and have proven to be a major headache for authorities and others.
The following are ten of the worst of the introduced species.
- The European rabbit (Oryctolagus cuniculus) was introduced into Australia in the 18th century for the purpose of recreational hunting. A release into the wild in 1859 saw them quickly become widespread. The winters were mild and the rabbits bred all year.
Even a rabbit-proof fence built from north to south across the country could not stop them entering Western Australia.
They are now found extensively throughout Australia. The introduction of myxomatosis gave a measure of control until the rabbits built up a genetic resistance to it. Calicivirus (RHD) has also been used.
- The red fox (Vulpes vulpes) was introduced in 1855, also for recreational hunting purposes. They are found over most of mainland Australia and there are small numbers in Tasmania. The threat level from the fox is estimated to be extreme.
They are an elusive and prolific predator of native animals and livestock. With the increased interest in controlling the population because of the impact on our native wildlife, there is now an attempt at controlling their numbers by laying baits. Baits containing fluoroacetate (1080) are effective in the south-west of Western Australia as some of the indigenous plants contain the same substance and the local wildlife is immune to it. However the poison affects quolls and the Tasmanian devil in other areas.
- The dromedary [camel] (Camelus dromedarius) was introduced from India in 1840 as a beast of burden. It was used as a draught animal to cart goods into the agricultural areas and to bring wool and other produce back to the coast. When motorised transport took over, some camels were simply let loose to fend for themselves and some escaped.
They are now found extensively throughout Central Australia where the arid conditions suit them perfectly. Their threat level is placed at medium to high. Helicopter culling is carried out from time to time.
- The feral goat (Capra hircus) also began with escapees or deliberate releases. The goat is another animal which has found the Australian climate very much to its liking and, on outback stations, it competes with sheep and cattle for what little food and water is available.
There have been some attempts to muster them and export them for their meat but the quality is variable and methods somewhat haphazard. Helicopter culling is sometimes attempted but numbers are so great that the method is likely to have little permanent effect.
- The feral pig (Sus scrofa) was also brought in as domestic livestock. They were introduced in 1788. There is now an estimated 13 to 23 million of them.
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They are prolific breeders, difficult to control as they are wily and adept at losing themselves in the bush. They destroy the environment, spoil natural watering points and have the potential to spread disease. There is some attempt at control wild pig populations by ground and helicopter culling, poisoning, trapping and mustering.
- The donkey came out in the early days along with all the other types of domestic animals. Again they flourished in the mild climate and they are a significant problem on the stations of the outback.
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Like all the feral animals that graze, they compete with both native and domestic stock for available food and water.
Any non-native herbivore competes with native species for (often) limited grazing.
- Feral cats are the most widespread and invasive of all introduced species. Cats decimate native wildlife. They are very efficient hunters and it is highly likely that the feral cat has been responsible for the extinction of some species of small mammals. Shooting and trapping are measures used against the feral cat. On small islands, these controls have been reasonably effective and some islands have been restocked with native animals.
- The cane toad (Bufo marinus) looks like being the most harmful of all the invasive species. It was brought into Queensland to combat the cane beetle but has since begun an inexorable spread right across the Top End of Australia and is now heading down the west coast.
It has poisonous glands behind the head. The native eastern quoll has been decimated in parts of its range as it eats the toad and is poisoned. Even the tadpoles are toxic. Birds, lizards and snakes are succumbing too. The black kite has learnt to flip the toad on its back and attack the soft belly thus avoiding the poison glands. The saw-shelled turtle appears to be immune to the poison too. There is a spate of scientific research happening in a bid to find some means of dealing with the numbers. Females lay single clump spawns which contain thousands of eggs. They eat anything and everything.
- The Common Indian Mynah bird (Acridotheres tristis) is another invasive pest. It was introduced in 1860 on the east coast. It was first introduced to eat insect pests. After land clearing, it is the number one threat to native birds.
The mynah is an aggressive bird, hunting away native species, competing for nests and even turfing out other chicks. Even small mammals such as the feather-tailed glider are threatened by these birds. Commonly called the 'garbage bird', it finds rich pickings wherever there is human habitation. This cocky brown and black bird with the yellow eye-patch is listed by the IUCN in its '100 of the World's Most Invasive Species'.
- The rock pigeon or rock dove (Columba livia) is an invasive species in many countries. In the wild, they are grey with two black bars on the wings. Feral populations can be a variety of colours and can be seen in their thousands in towns and cities.
The faeces of the rock pigeon are acidic and cause damage to property including stone buildings and monuments. Pigeons are usually monogamous and have two chicks or squeakers per brood.
Other introduced invasive species include the water buffalo and common starling. Feral horses (brumbies) are sometimes culled, usually amid great controversy. The dingo was introduced before Europeans arrived on the continent but is now mostly considered a 'native' animal.