Australia's indigenous plants and animals adapted to life on an isolated continent over many millennia.
Introduction of many feral animals (examples right) was done with good intent without future proper scientific foresight.
For example, the Common Myna was originally introduced into the cane fields of north-eastern Queensland in 1883, to combat insect pests, particularly plague locusts and cane beetles.
European settlement has given the undesirable need for our indigenous animals and plants to compete with a range of introduced animals for habitat, food and shelter. Many have also had to face new unforeseen predators. These new pressures and stresses have also had a key impact on not just the Tootgarook Swamp's waterways, soil and indigenous plants and animals, but all of Australia.
In Australia, feral animals typically have few animals that prey upon them, or even lethal diseases. Just like introduced weeds the feral animals have left their disease organisms and their predatory animals, and weather conditions behind in their originating environment.
As a consequence, feral animal populaces have not been kept in check by their natural ecosystem and many can reproduce rapidly if conditions are favourable.
Feral animals can affect indigenous species by spreading diseases, preying upon, providing direct competition for food and shelter, and destroying habitat.
Feral animals can convey the same common diseases as domestic animals, and can be a continuous source of reinfection for indigenous animals and domestic livestock, which works against all labours to control costly diseases such as tuberculosis. Feral animals are also potential carriers of parasitic diseases (such as tapeworm, heartworm, liver fluke) and other animal diseases and fungus (such as rabies, foot and mouth disease, Phytophthora and Myrtle rust).
So far luckily many potential diseases do not occur in Australia, though an outbreak among Australia's native animals would have an immediate and widespread effect, and would be disastrous for our environment.
Many indigenous birds that live in hollows, and some of those that create nests are pushed out, including their eggs or young, by feral birds such as the introduced Common Myna. Feral animals such as rabbits graze or degrade vegetation that provides food and shelter for many indigenous animals. If indigenous plants are damaged and destroyed, or consumed by feral animals, the food and habitat for indigenous species is placed under greater pressure.
Feral cats and foxes hunt and kill indigenous birds, mammals, reptiles and insects, as well as can increase the spread of noxious weeds, such as blackberries.
It is known that this behaviour threatens the existence of many endangered and protected species, of the 21 completely extinct marsupials and rodents in Australia, the red fox and cat have most almost certainly contributed to the extinction of all but two.
Feral animals can also cause soil erosion, while managed domestic livestock can be removed from despoiled areas until these areas are revegetated and restored, it is much more difficult to keep feral animals out of these same areas.
Just like plants the common names used for description of our animals is a threat to the unknowing and innocent, furthering why education is important. The word common before many animals makes it hard to distinguish if it belongs, and can also sound ordinary, or equal. Other names such as such given to the Eurasian Coot an indigenous bird make it sound like it doesn't belong, where as the Eurasian Skylark is introduced.
 Birds in Backyards www.birdsinbackyards.net/birds/featured/Introduced-birds
 Department of Sustainability, Environment, Water, Population and Communities www.environment.gov.au/biodiversity/invasive/publications/pubs/pest-animal-strategy.pdf
 Invasive Species Council http://www.invasives.org.au/page.php?nameIdentifier=feralanimallandingpage