The domestic cat (Felis catus) was introduced to Australia by Europeans and now inhabits all of mainland Australia, Tasmania and a number of offshore islands. Feral cats are opportunistic, generalist carnivores and their potential impacts include: predation, competition and disease transmission.
The recent Action Plan named feral cats as the number one threat to endangered mammals and Federal Environment Minister, Greg Hunt, has called for the 'eradicat[ion] of all significant populations of feral cats' within a decade.
Cats prey on at least 400 native and introduced vertebrates in Australia, including 123 birds, 157 reptiles, 58 marsupials, 27 rodents and 21 frogs. Cats have played a key role in the extinction of at least 22 mammals, and are a current threat to several threatened mammal and bird species. Most evidence for the population-level impacts of feral cats has been gleaned from historical patterns of decline and extinction, or from the failure of reintroduction attempts for threatened mammal species. The small amount of experimental work that has been done confirms that cats can suppress and exterminate small mammal populations.
The impacts of competition and disease transmission are less clear. Overlap in resource use between cats and native predators suggests competition may exist, although this has not been confirmed experimentally. Cats carry the parasite Toxoplasma gondii, which can cause death for many marsupials. High prevalence of Toxoplasma antibodies has been recorded in some marsupial populations, although it is not known how infection might alter their behaviour or susceptibility to predation.
Further research into the non-lethal impacts of cats is necessary, as well as a better understanding of the relationship between cats, other predators and their prey.