Government estimates of feral cat populations have been found to be off by millions in a new study.
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The study, led by Sarah Legge from the University of Queensland, has revised the number of the feral animal from the popularly used figures of 15 million-20 million to 2.1 to 6.3 million, making the government's target to eradicate 2 million of the animals between 2015 and 2020 even more "ambitious".
The study, which found feral cats now covered 99.8 per cent of Australia's land mass, questions the target set by the government and how useful it may be in achieving the goal.
"This particular target may not provide a useful measure of conservation benefit, nor may it be readily measurable, and it may become an example of Goodhart's Law - that once a target is set, management effort becomes focused on achieving the target in the most efficient way rather than solving the problem to which the target relates," the study reads.
"For the culling of 2 million cats to be a defendable target, it must be contextualised with reference to the total number of feral cats in Australia."
Dr Legge said the numerical targets might be beside the point when it came to protecting native species from the feral cats.
"It's more about the impact the cats have than the numbers they kill, for example you don't need to kill many of a native species to have a massive impact," Dr Legge said.
"Cats are quite unusual predators, they become specialised with certain prey, so if you have a cat that likes bilbies, that cat will keep hunting bilbies even when bilbies become rare in the landscape, it will keep searching for them until it gets rid of the last one."
Australia's threatened species commissioner Gregory Andrews said the damage feral cats had done was clear, with the animals being responsible for two-thirds of mammal extinctions in Australia.
"We can't afford to take the foot off the pedal. With 144 species at risk, we're committed to the 2 million feral cats by 2020 and I'm really looking forward to escalating our efforts in the year ahead," Mr Andrews said.
"(Environment Minister Josh) Frydenberg, in the new year, will be launching a new threatened species strategy perspective, which is an invitation to the private sector to invest in threatened species conservation."
The research, funded by the federal government's National Environmental Science Programme, suggests targeting specific populations of feral cats may be the only way to have a meaningful effect on conservation in Australia.
The origin of the 15 to 20 million estimate used by the government to set eradication targets, Dr Legge said, was traced back to a speech given by a New South Wales MP in 1993, who she suspected was using a rough estimate given to him by a scientist.
The massive drop in numbers from the new estimate comes from studying nearly 100 regions, with different climates and resources, to get a more accurate reading of population densities across the country and its islands.
The fluctuations in the estimate population are due to condition, in the leaner seasons and years the numbers of feral cats die back, but this is where they can be at their biggest risk to the environment.
"When you get extensive rains in the arid zones of Australia you get a pulse in prey density and the cats breed very quickly on the back of that," Dr Legge said.
"The real drama comes when the place dries out at the end of that rainfall event, because suddenly the prey numbers crash and you have this plague of cats with nothing left to eat.
"That's when they can do their most damage, because they'll hunt so persistently that they'll remove every last individual prey animal from the landscape."
