In his excellent 2006 book Australia's Mammal Extinctions - a 50,000 year history, Chris Johnson of James Cook University makes the comprehensive case for the role of feral cats in causing extinctions. He concludes that with the exception of the toothache wallaby, cats and foxes can account for practically all of the mammal extinctions of the last two hundred years.
There are many people that have, quite correctly, questioned the role of feral cats. Tim Low does so in Feral Future and Tim Flannery has done in the ABC special Ten million wild cats. However, the case against the cat becomes more and more compelling as we understand more of the interactions of cats and other factors in the environment.
In his book Animal Nation (2006), Professor of Sociology at the University of Tasmania, Adrian Franklin argues that we should accept feral animals as part of country. Our "species-cleansing" attitude is derided and Franklin argues for acceptance of humanity as simply another agent of nature, and to accept the changing mix and balance of species as inevitable, and given. He uses the fact that the feral cat has become a totem animal in some Aboriginal families as evidence that environmentalist's views of feral animals are more bound to national history than natural history.
Franklin goes much further than Low or Flannery who question the case against the cat. He doesn't go as far as some animal rights people that deny any environmental damage by cats in order to make the argument that we should just leave them be.
It might be worth looking at a few of the controversial issues about feral cats:
Cats arrived before white settlement. Their role in dreaming stories is evidence of this. Wrong. Ian Abbot (2002) looked hard at the issue of when cats were introduced and there is no evidence it predated white settlement. Aboriginal dreaming stories can develop reasonably quickly - when Andrew Burbidge and colleagues followed oral histories of animals, they even encountered a tractor dreaming site. In the western deserts, cats would have arrived probably a generation ahead of white settlement, so the fact that cat dreaming might not be associated with white settlement is not surprising.
Environmentalists in Australia persecute cats. Not really. Budgets are small and the tools for cat control are few. I don't know of any programs where people get budget and approval to simply go out and kill feral cats. I sit as an observer on the inter-government Vertebrate Pests Committee and everyone is on about impact reduction, not simply feral animal numbers. Certainly there is research going on to try and make cat control more effective, but most programs would be associated with clearing an island, sanctuary or reintroduction site.
Cats are widespread across Australia and overlap with small mammals (especially in Tasmania), therefore they don't drive small mammals to extinction. This view fails to take into account other factors in the environment. Rainfall is one - cats are most effective as hunters in areas that are open, with sparse vegetation due to low rainfall. Predation on cats is another - for example, numerous extinctions did not occur until Aborigines, who regularly hunted cats, left the land.
It's this last point that I have most concerns about. Things change in the environment and so cats can become a problem. I don't think it is necessary to have a level of proof equivalent to a murder trial before we act. For example:
Researchers in the Northern Territory are reporting significant declines in small mammals in Kakadu National Park. More regular burning patterns could be opening the country up to cat predation.
Woylie (brush-tailed bettong) numbers in the South West of Western Australia have crashed. Gathering evidence points to "mesopredator release" - that is, cats becoming more important predators as a result of fox control - as at least part of the cause.
Tasmanian researchers report it is a lot harder to find a range of species in recent monitoring efforts. Widespread demise of Tasmanian Devils might be responsible for rising feral cat populations.
In none of these cases do we have definitive proof of the role of feral cats. But that is not a reason to simply sit back and accept them as an agent of nature, as Adrian Franklin puts it. I can't abide this extreme Darwinism point of view and agree with the 7 out of 10 Australians that put feral cats in their "top 5" ferals of concern.
I argue we should do more about feral cats, ahead of getting definitive proof of their role in extinctions.