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] As one of the most ecologically damaging and the most costly invasive species in Australia, predation by both domestic and feral cats has played a role in the extinction of many of Australia's indigenous animals. For instance, cats are found to have significantly contributed to the extinction of at least 22 endemic Australian mammals since the arrival of Europeans.[5]
Historical records date the introduction of cats by the first settlers in 1788 and that cats first became feral around Sydney by 1820.[6] In the early 1900s concern was expressed at the pervasiveness of the cat problem.[7]
Domesticated cats
Each pet cat in Australia kills an estimated 110 native animals each year; totalling up to about 80 million native birds, 67 million native mammals and 83 million native reptiles being killed by them annually.[8]
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.[12] A study in the 2010s estimated that each feral cat kills 740 wild animals per year.[13] 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.[14] 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.[15][16]
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.[17] 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.[18] Cats in Australia have no natural predators except dingoes and wedge-tailed eagles, and as a result, they are apex predators where neither the dingo nor the eagle exists.[19] Also, dingos do not appear to affect the activity of cats.[20]
Claimed benefits
Some researchers argue that feral cats may suppress and control the number of ratsand rabbits, and cat eradication may damage native species indirectly.[21][22]
Economic impacts
Cats are the costliest invasive species in Australia.[23] 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.[24]
Since 2016, a program on Kangaroo Island aims to fully eradicate the island's feral cat population, estimated at between 3000 and 5000, by 2030.[28][29] The 2019–2020 bushfires have complicated the eradication efforts, as the gradual regrowth of the burnt brush creates favourable conditions for cat breeding and makes them more difficult to hunt.[30] 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[31] 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.[32]
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.[34] Subsequent DNA tests showed it to be a feral cat.[35]
^"The Cat Problem in Australia". The Sunday Times. Perth, Western Australia: National Library of Australia. 22 December 1912. Christmas Number, 3rd section, p. 8. Retrieved 21 January 2016.
^Davies, Wally; Prentice, Ralph (March 1980). "The feral cat in Australia". Wildlife in Australia. 17: 20–26, 32. Retrieved 21 January 2016.
^Risbey, Danielle A.; Calver, Michael C.; Short, Jeff; Bradley, J. Stuart; Wright, Ian W. (2000). "The impact of cats and foxes on the small vertebrate fauna of Heirisson Prong, Western Australia. II. A field experiment". Wildlife Research. 27 (3): 223. doi:10.1071/WR98092.
^Moseby, Katherine E., et al. "Interactions between a top order predator and exotic mesopredators in the Australian rangelands." International Journal of Ecology 2012 (2012).
^Fancourt, Bronwyn A., et al. "Do introduced apex predators suppress introduced mesopredators? A multiscale spatiotemporal study of dingoes and feral cats in Australia suggests not." Journal of Applied Ecology 56.12 (2019): 2584-2595.