COVID-19 travel restrictions are limiting the ability of experts to monitor the recovery of threatened species after the bushfires, leading ecologists have warned.
Meanwhile new research indicates up to three billion animals could have been in the path of the fires - three times as many as originally predicted.
Australian Academy of Science fellows, Professor David Lindenmayer and Professor Chris Dickman will give evidence to a Senate inquiry looking at the 2019-20 bushfires on Wednesday.
A briefing note to be released by the Australian Academy of Science says the coronavirus pandemic has disrupted efforts to collect data on the ground about how species impacted by the fires are recovering.
In particular, the Threatened Species Committee - which had prioritised assessments of species within the fire scar - had been "compromised" by travel constraints, which were "seriously limiting immediately necessary on-ground monitoring".
The Department of Agriculture, Water and Environment,which had been monitoring the recovery of species in tandem with other organisations, also had its work restricted by safety concerns.
Professor Dickman said the coronavirus restrictions could not have come at a worse time.
"Many of the worst effects of the bushfire happen in the immediate aftermath. That's when resources animals need are most badly affected and when predators are most likely to move in. That period we were unable to do any monitoring [because of COVID-19]," Professor Dickman said.
"It's been really heartbreaking, with the fires ending in February and the COVID lockdowns beginning in March, it's really stymied attempts to get out in the field."
Professor Lindenmayer said it had been "hugely challenging" to complete fieldwork with the coronavirus restrictions in place.
"For example last week we were doing field survey work in south-western NSW, on the border with Victoria, normally we'd all get together and teams would work across the whole survey sites, but it wasn't possible to get across the border," Professor Lindenmayer said.
Even before the fires and pandemic, there was a lack of long-term monitoring of threatened species in Australia, Professors Dickman and Lindenmayer said.
"We weren't in a good position before the fires. Monitoring was so run down prior to the fires, we didn't really have a good handle on the population numbers of many species throughout our forest estate. Over the last two decades it seems to have been significantly wound back," Professor Dickman said.
Professor Lindenmayer said funding for the Long Term Ecological Research Network was cut in 2017, after only six years of monitoring.
"Funding for the centre was $1.3 million per year which is trivial compared to the $100 billion impact of the fires but it was axed in 2017. It was one of the most ridiculously shortsighted things you could imagine," Professor Lindenmayer said.
Professor Dickman said some species which were not listed as threatened had seen a dramatic decline in populations.
"The greater glider, the yellow-bellied gliders. These used to be common," Professor Dickman said.
The brush-tailed possum is not a threatened species but it's lost three-quarters of its range. It used to occur in central deserts in areas with no trees, it used to find shelter under rock crevices. The last population in the MacDonnell Ranges is now extinct.
"These are species that because we see them in our gardens, parks and cities, we think they're doing okay but in terms of their bigger distribution, they're not actually doing that well."
It comes as research commissioned by WWF-Australia estimates nearly three billion animals may have been in the path of the bushfires.
The estimate includes 143 million mammals, 2.46 billion reptiles, 180 million birds, and 51 million frogs.
In January, Professor Dickman estimated 1.25 billion animals may have been affected by the fires.
The figure is contained in an interim report compiled by 10 scientists from the University of Sydney, University of New South Wales, University of Newcastle, Charles Sturt University and BirdLife Australia.
While scientists are unable to say how many of these animals may have perished, Professor Dickman said the prospects for animals which escaped the flames were "probably not that great" because of a lack of food and shelter.
WWF-Australia chief executive Dermot O'Gorman said it was difficult to think of another event worldwide that has killed or displaced that many animals.
"This ranks as one of the worst wildlife disasters in modern history," Mr O'Gorman said.