Cats (Felis catus), initially introduced into Australia with the First Fleet in 1788, are the second most popular household pet. They are also considered by the CSIRO to be the most damaging invasive pest by cost^[1] and fourth most damaging overall to the environment.^[2] There are estimated to be up to 6 million feral cats distributed across more than 90% of the continent including every major island.^[3]

The Invasive Species Council has estimated that each year domestic and feral cats in Australia kill 1,067 million mammals, 399 million birds, 609 million reptiles, 93 million frogs, and 1.8 billion invertebrates.^[4] Cats are found to have significantly contributed to the extinction of at least 22 endemic Australian mammals since the arrival of Europeans.^[5]

Feral cats are extremely difficult to control, are capable of bypassing control barriers and have adapted to harsh desert conditions by burrowing and obtaining sustenance by preying on moisture-rich small desert marsupials. Their economic burden of more than A$18.7 billion annually since 1960, nine times that of rabbits.^[1] Cats carry disease including toxoplasmosis which impacts human and livestock at a cost of more than AUD $6 billion annually.^[6] Australia remains rabies free and for biosecurity reasons, any cats that are imported into Australia must meet conditions set by the Department of Agriculture, Fisheries and Forestry.^[7]

Several native species have evolved cat-like characteristics through a process of convergent evolution, including the marsupial quolls, known as a "native cat" which occupied a similar environmental niche to the introduced cat.^[8] DNA studies have ruled out any introduction of the mammal felis catus prior to the arrival of Europeans including Asian introductions or 17th century shipwrecks.^[9]

Historical records date the introduction of cats to the First Fleet in 1788.^[9] In 1824, Edward Henty brought cats to the Portland Bay district in what is now Victoria.^[10] Based on accounts from local Aboriginal people, it is thought that cats were brought to the Swan River Colony (now Perth, Western Australia) from Britain during its 1829 foundation.^[11] Most early Australian cats are believed to have been offspring of these introductions.^[10] As a result, cats as household pets were rare until the 1830s when they began to grow in popularity, particularly due to their ability to control rodents in rapidly growing urban areas.^[12]

The first feral cats were recorded in Sydney in 1824 and in Western Australia in the 1840s.^[12] With a growing agricultural industry, in the 1860s cats were deliberately introduced into agricultural areas outside of the main settlements. In 1864 a mass release of cats in the Lachlan River in New South Wales were aimed at controlling a rat plagues.^[12] Similar introductions to control rodent plagues occurred in rural areas of Western Australia and Victoria in the 1860s, the Warrego River in Queensland in 1874.^[12] Cats were seen as particularly effective at controlling occurrences of the bush rat or dusky field rat in farming land.^[12]

By the mid 1860s, cats were themselves at times considered a pest. At Barwon Park, Victoria in 1868, one of the first recorded cullings occurred, with over 100 feral cats found to be nesting in rabbit burrows.^[12]

Cats were first released as rabbit control in the 1880s in Victoria's Wimmera promoted under government policy, as well as outback South Australia.^[12] While their ability to catch rabbits was often praised, rabbit trapping was considered a far more effective method and the releases simply aided the cat's spread across outback Australia.^[12] Observers in far outback Queensland and New South Wales noted that cat populations had begun to grow in number during the 1880s.^[12] The first recorded "plague" of wild cats occurred in Thargomindah in 1888 after which local farmers began to place a bounty on them.^[12]

By 1890 cats had spread to their approximate current mainland distribution of over 90%.^[13] Feral populations were growing in remote Western Australia and Victoria in the late 1890s.^[12] Despite this, they continued to be released throughout remote areas of Australia in an effort to control rabbits.^[12] For many decades the problem of feral cats was often overlooked as for many it was sight unseen, with cats most actively hunting at night.

In the early 1900s concern was expressed at the pervasiveness of the cat problem.^[14]

The 1920s saw a change of opinion and some began to regard the introduction of cats for pest control as a failure and proclaimed them a pest. The Naturalist, writing for the Australian, was of this sentiment.^[15] Professor Wood Jones attributed the threat of bird and marsupial life in the outback to the practice of dumping kittens in rabbit warrens in outback cattle runs.^[16] British naturalist Dr Leach in 1923 wrote of a startling decline in Australian birdlife, particularly parrots and concluded that feral cats have "got to be reckoned with".^[17] Feral cats were also, by this time, present on most islands.^[18] The Royal Society of South Australia met to discuss the issue in 1927.^[19] A war was declared on cats in 1929 were common in rabbit burrows, grew far larger than domestic cats, and began to be hunted for their skins.^[20]

During the 1950s, Myxomatosis was introduced in an effort to control rabbits. This had the effect of cats searching for other sources of food.^[21]

In the 1970s the belief that pet owners were responsible for the feral cat problem became common. This was partly due to an increase in the prevalence of feral cats in urban areas, many believed to be strays.^[22] It was also because the RSPCA placed the blame on those disposing of unwanted kittens in the bush and called for pet ownership restrictions.^[23] Popular opinion was that most feral cats originated as unwanted or uncontrolled house cats.^[24][25][26] Cats became a particularly bad problem for on King Island to pheasant populations where groups were lobbying authorities to introduce bounties.^{[27][28][29][30]} Cats up to a metre long were shot in Western Australia.^[31]

Prior to the late 1970s opinions as to whether the red fox or cat was the bigger pest tended toward the fox. However in the late 1970s and early 1980s local extinctions of marsupials began to be attributed directly to feral cats.^[32] Cats were the bigger pest, according to experts in the early 1980s, especially to endangered birdlife.^[33][34][35] Cat eradication programs began to be called for on some islands such as Reevesby Island.^[36][37]

A feral cat eradication organisation was formed in 1991.^[38]

Domesticated cats that are allowed to roam kill an estimated 110 native animals per cat each year; totalling up to about 80 million native birds, 67 million native mammals and 83 million native reptiles being killed by them annually.^[39]

Almost 30% of Australian households keep at least one domesticated cat.^[40][41] Domesticated cats must be microchipped in every state of Australia except Tasmania.^[42] All pet cats past six months of age must be desexed in the Australian Capital Territory, Tasmania, South Australia and Western Australia.^[43]

Feral cats are a major invasive species and have been linked to the decline and extinction of various native animals in Australia. They have been shown to cause a significant impact on ground-nesting birds and small native mammals.^[44] A study in the 2010s estimated that each feral cat kills 740 wild animals per year.^[45] Feral cats have also hampered attempts to reintroduce threatened species back into areas where they have become extinct, as the cats quickly kill the newly released animals.^[46] Environmentalists conclude that feral cats have been an ecological disaster in Australia, inhabiting almost all of its ecosystems, and being implicated in the extinction of several marsupial and placental mammal species.^[47][48]

A field experiment conducted in Heirisson Prong (Western Australia) compared small mammal populations in areas cleared of both foxes and cats, of foxes only, and a control plot. Researchers found the first solid evidence that predation by feral cats can cause a decline in native mammals. It also indicates that cat predation is especially severe when fox numbers have been reduced.^[49] Cats may play a role in Australia's altered ecosystems; with foxes they may be controlling introduced rabbits, particularly in arid areas, which themselves cause ecological damage. Cats are believed to have been a factor in the extinction of the only mainland bird species to be lost since European settlement, the paradise parrot.^[50]

It is sometimes falsely believed that cats in Australia have no natural predators and as such are apex predators.^[14] While this is true in some areas, cats are both preyed upon and outcompeted by both native and introduced animals. Studies of the diet of Tasmanian devils found scats of 14% of them contained cat DNA.^[51] It is strongly suspected that they specifically hunt kittens in wild burrows.^[51] Combined with competing for prey they have successfully suppressed feral cat populations in Tasmania in areas free of devil facial tumour disease.^[52] Due to this proposals to reintroduce devils to the mainland often cite reduction of feral cat numbers as a key benefit.^[53] Likewise stomach and scat evidence shows that dingoes (and feral dogs) prey upon them^[54] and in areas where they are common, there is evidence that feral cat populations are supressed,^[55] though some dispute this.^[56] Some believe that red foxes help suppress cats because cats boom in numbers when foxes are removed from an area.^[57][58] However cats are only part of their diet; adult cats generally survive stand offs and elude them by outrunning and outclimbing.^[14] Some snakes, particularly the carpet python and eastern brown snake kill cats,^[14] however adult cats are generally more a threat to native snakes due to their ability and speed they are capable of evading most strikes.^[59] In some remote areas wedge-tailed eagles and saltwater crocodiles are known also to prey on them^[60][61] though this is not common.

Some researchers argue that feral cats may suppress and control the number of rats and rabbits, and cat eradication may damage native species indirectly.^[62][63]

Cats are the costliest invasive species in Australia.^[64] The cost of invasive cats to the national economy is estimated to be nearly A$19 billion over the 60 years up to 2021, with most of the cost spent on population control. This cost significantly outstrips the next most costly invasive species, with rabbits in Australia coming in at nearly A$2 billion.^[65]

Cats are notoriously difficult to control due to being able to burrow, jump climb and breed prolifically.^[66] They can climb over artificial barriers and resist trapping and baiting. Cat control strategies are outlined in the Department of Climate Change, Energy, the Environment and Water's Feral Cat Threat Abatement Plan first published in 2008.^[67] Use of dogs to detect the presence of cats has been highly effective.^[68]

Trapping success is varied as most cats resist trapping due to their cautious nature.^[69] Trap–neuter–return is the method most favoured by animal welfare groups.^[70] While many cats are captured this way, the logistics are difficult in remote regions,^[71] and some studies suggest it only stabilizes cat populations.^[70]

Shooting is seen by many as the only effective form of control with ground shooting is the most common and resource intensive.^[66] Aerial shooting is difficult due to their size and ability to climb, burrow and survive injury. Shooting in general is largely ineffectual due to the high costs and that it does nt address the source of the problem. Historically shooting has been opposed by animal welfare groups and continues to be discouraged.^[72] Some varmint hunters, such as Barry Green, face backlash and even death threats for the culling of the feral cats.^[73][74]

Baiting is used as most native animals have a high tolerance to it, but its use with cats is seen to be generally not effective. Cats prefer live game and are tolerant to high doses, so specialised baits are required for cats. Baiting is expensive and its effectiveness as a means of control for cats is inconclusive. Furthermore baiting in some jurisdictions, such as Victoria and Queensland, is subject to restrictions.^[75] Animal welfare groups advocate for alternatives due to it being a less than humane option.^[76]

Exclosure fences capable of stopping cats from entering or exiting an area required complex construction and are extremely expensive.^[77] This is usually used to create a "safe haven" from cats. As such the best natural barrier, water, makes control on islands less difficult.

The idea of reintroducing Tasmanian devils has been proposed, due to their effectiveness in cat control in areas where they are present, however has not gained traction.^[53]

Pintupi, Nyirripi and other Western Desert peoples in Western Australia and Northern Territory have been hunting cats to use as a food source and for bush medicine for decades, but in 2015 they were also participating in a program with ecologists to help monitor and reduce cat predation on threatened species.^[78]

In 2016 the federal government announced a program to eradicate cats from Bruny Island, French Island, Christmas Island, Dirk Hartog Island and Kangaroo Island.^[79]

Kangaroo Island's population is estimated at between 3000 and 5000 and is targeted at being cat free by 2030.^[80][81] The 2019–2020 bushfires complicated eradication efforts, as the gradual regrowth of the burnt brush creates favourable conditions for cat breeding and makes them more difficult to hunt.^[82] By the end of 2021, at least 850 cats had been removed from the burnt area at the western end of the island using grooming traps with state-of-the-art technology^[83] and cameras. In addition, an exclusion fence had been built on private property around some of the burnt land, helping to protect the populations of Kangaroo Island dunnart and southern brown bandicoot.^[84]

The numerous sightings of phantom cats in Australia include the Gippsland phantom cat and the Blue Mountains panther.^[85]

Australian folklore holds that some feral cats have grown so large as to cause inexperienced observers to claim sightings of cougars in Western Australia. While this rarely occurs in reality, large specimens are occasionally found: in 2005, a feline was measured to be 176 cm (69 in) from the tip of its nose to the tip of its tail in the Gippsland area of Victoria.^[86] Subsequent DNA tests showed it to be a feral cat.^[87]

• Hunting in Australia
• Threatened fauna of Australia
• Environmental issues in Australia

• Feral Cat Felix catus, Department of Sustainability, Environment, Water, Population and Communities
• Predation by feral cats - Threat abatement plan - Department of Sustainability, Environment, Water, Population and Communities
• Management of cats in Australia - Australian Veterinary Association
• Australian Companion Animal Council
• Shooting Cats: Australia's War On Feral Cats on YouTube