The sheer magnitude of plant and animal species potentially wiped off the face of Australia by unrivalled bushfires is unknown.

But when the fires that have torn through a combined area almost as big as England eventually ease, scientists fear a brutal outcome.

Most of the animals that escaped the unprecedented crisis will eventually perish.

"Even the animals that haven't immediately been killed from the fires and the smoke, most of those that are displaced will eventually die," Professor Martine Maron said.

Predators like foxes and cats will thrive, buoyed by easy pickings and room to move.

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Professor Maron, from the University of Queensland's School of Earth and Environmental Sciences, said surviving wildlife will either starve or be eaten.

"For a lot of our fauna, it will mean there are no food resources, no shelter, for a long time in some cases, while these areas recover," she said.

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"The problem is there aren't a lot of unburnt refuges through these areas, and of course, where there are unburnt areas of habitat, there are already other animals there using it.

The fires have claimed at least one billion animals, according to University of Sydney environmental sciences professor Chris Dickman.

NSW National Parks and Wildlife Service

That figure only takes in birds, reptiles and mammals, excluding bats, frogs, insects and other invertebrates.

It is being described as conservative, as government officials and non-government experts rush to map the real toll.

Some of Australia's leading conservation groups fear a catastrophic impact on endemic plants and fauna including koalas, the glossy black cockatoo, regent honeyeater and long-footed potoroo.

"This is not an exhaustive list, it is literally the tip of the iceberg," Australian Conservation Foundation's James Trezise said.

"The reality is going to be quite brutal."

Ecosystems that rely on many parts working together could collapse.

"We've got almost 2000 threatened species and ecosystems in Australia ... let alone the other species that aren't listed as threatened, that meet that threatened criteria after these events," Mr Trezise said.

"So what we're going to see is new threatened species emerge out of this as well."

There were just 38 eastern bristlebirds left before the fires, and Birdlife Australia's head of conservation, Samantha Vine, is clinging to a tiny piece of good news.

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"We know that some of the habitats in Queensland have been impacted, but I've just heard today that it sounds like a lot of their stronghold in New South Wales was spared," she said.

While the governments, scientists and communities come to grips with the immediate aftermath of the fires, an unknown flow-on effect will lurk.

"It's really important that the science gets out there so that it is understood by everybody just how widespread the impact of these sorts of events are," Professor Maron said.

"The good sign is, I think that message really is getting through, and people are pushing hard for a positive response, to try to help things to recover from this immediate event, and to put things in place to prevent the worst."

With AAP.