Feral cats have taken over Australia, including its national parks, and more native species will die off without drastic action, experts say.

A new study by leading environmental scientists shows feral cats have spread across 99.8 per cent of Australia's land mass.

They are present in all terrestrial ecosystems and in every region of Australia, from our biggest capital cities to every one of our largest offshore islands.

In fact, the only place you won't find them is on some smaller islands, and selected mainland areas specifically fenced to keep out cats and foxes.

Scientists have also found there are just as many feral cats inside national parks and other conservation zones as outside them, meaning they aren't much help to native species that serve as prey.

Lead study author Dr Sarah Legge, from the University of Queensland, says the spread of feral cats has increasingly pushed land mangers towards expensive conservation measures.

She says fenced-off predator-free zones on the mainland have been costly but effective, but they are relatively small.

She believes future efforts must include a stronger focus on establishing island refuges, because unlike the mainland, they can be cleared and kept free of cats.

"The federal government has a target of culling 2 million cats over five years. That's very good, it's very ambitious," she told AAP on Wednesday.

"But it's going to be very important to target cat culling to achieve the greatest benefit for wildlife.

If you get rid of cats on larger islands, you can then stop their reintroduction with biosecurity measures, and then you have a big area that's safe for wildlife."

Australia's feral cat population fluctuates between about 2 million, in lean times, and 6.3 million when there has been good rain, and prey is plentiful.

But cats are also prolific breeders, compounding the problem for wildlife managers.

Australia's Threatened Species Commissioner Gregory Andrews agrees a targeted culling program is an essential part of the solution.

"Australia is the only continent on earth other than Antarctica where the animals evolved without cats, which is a reason our wildlife is so vulnerable to them," he said.

Australia has already lost at least 20 mammals to feral cats.

The research, by more than 40 scientists, brought together almost 100 different studies on Australia's feral cat problem. It was funded by the Australian government to better inform management plans and has been published in the science journal Biological Conservation.