As Australia’s unprecedentedly catastrophic bushfires rage, the emerging images are apocalyptic: skies turned blood red by smoke, families sheltering on boats to escape the flaming shore, and landscapes littered with the charred bodies of iconic animal species such as kangaroos and koalas. The plight of the continent’s famously unique fauna has garnered particular attention around the world. One estimate says that just in the state of New South Wales, about 800 million animals have likely been affected by the fires. But it is unclear how many have perished outright.

Fires have been part of the Australian landscape for thousands of years. Many species and ecosystems have evolved to cope, with animals surviving in tree hollows and other refuges or repopulating burned areas from nearby unaffected land. But the severity and size of this season’s fires may limit the effectiveness of those strategies, several ecologists say. And as climate change fuels longer fire seasons and more frequent, intense fires, it could become increasingly difficult for ecosystems to bounce back. These changes “are potentially quite a major risk to our biodiversity,” says Sam Banks, a conservation biologist at Charles Darwin University in Australia.

It is impossible for scientists to know precisely how many animals have been killed until fires subside enough to allow surveys of the burned areas. Chris Dickman, an ecologist at the University of Sydney, extrapolated the known population densities of mammals, birds and reptiles over the more than 12 million acres burned in New South Wales to arrive at the 800-million estimate. If the fires in the states of Victoria and South Australia are included, that would push the number to more than one billion animals whose habitat has been on fire, Dickman says. This method is imperfect: animal densities differ in various places, and the numbers do not include several types of animals, notably bats, which make up one quarter of Australia’s native terrestrial mammal species. But “it’s as good an estimate as we’ve got,” Banks says.

Which creatures succumb to the blazes and which survive, at least in the short term, will vary from species to species and in ways that are not immediately obvious, Banks, Dickman and other ecologists say. The ability to fly may seem to be a means of escape for both birds and bats, for example. But Dickman notes that many of Australia’s forest bats are slow flyers—a tradeoff for maneuverability in the dense canopy—and may not be able to easily flee the fast-moving infernos, Dickman says.

Some animals are adapted to find refuges in rock crevices or burrows. Banks and several of his colleagues found that the mountain brushtail possum survived the 2009 “Black Saturday” fires, which devastated areas around Melbourne, by sheltering in tree hollows. The possums actually experienced less mortality from the fires than from year-to-year changes in water availability. Other species can repopulate a burned area with just a few survivors: the agile antechinus (a small marsupial akin to a shrew) saw a 70 percent drop in its numbers in the 2009 blazes but recovered to prefire levels over the following three years, Banks says. Still other animals can recolonize burned areas by moving in from neighboring patches of unharmed land.

These strategies are limited, though, where habitat is already fragmented—such as along the heavily populated coast of New South Wales or where a species is already rare. Dickman is concerned, for example, with populations of the black-tailed antechinus, a species only described in the past few years on the border of New South Wales and Queensland. “We don’t know what the effects will be, but the fires have covered a large part, if not all, of the known distribution of this species,” Dickman says. That is just one example of likely many. “Australia’s so diverse that no matter where the fires reach, it feels like you’re going to be wiping out something that’s going to be specific to that range,” says Anna Doty, a physiological ecologist at California State University, Bakersfield.

For animals that do endure fires, the threat is not over. They have limited food and water resources and little shelter from predators, circumstances that could cause further mortality in the weeks and months after the smoke clears. In Australia, invasive European red foxes and feral cats are known to swoop into burned areas to pick off survivors, Dickman says. Clare Stawski, a zoologist now at the Norwegian University of Science and Technology, found that more of the antechinuses she was monitoring after a 2013 fire in New South Wales succumbed to postfire pressures than were killed directly in the flames. “The long-term impacts can be very long,” she says.

The sheer scale of this season’s fires, in terms of both size and intensity, also works against animal survival—both during and after the fires. “These fires in Australia are so severe that I fear it doesn’t matter that these small animals can even find these refugia,” Doty says, noting that the heat may penetrate into crevices and hollows. And this time around, the burn scars will be so large that recolonizing their interiors will take an extremely long time, especially for slower-moving species, she says.

Climate change is expected to exacerbate the situation. Climate scientists have warned for years that rising global temperatures would bring more drought, longer fire seasons, and more frequent and intense fires to the part of Australia that is now ablaze. Even for scientists, who are acutely aware of the predictions, the current fires have been jarring. “To be honest, I didn’t realize that it would escalate so quickly to the level it is this year,” Stawski says.

One factor that helped species recover from the Black Saturday fires was abundant rainfall in subsequent months, Banks says. But he notes that drought conditions are now becoming more common, which could hamper recovery this time. (Much of southeastern Australia is currently in a major drought, which has contributed to the onset and severity of the recent fires.) And the mountain brushtail possums that survived the Black Saturday blazes might not be able to use the same shelter strategy in the future, Banks says, because the old trees where hollows are found are more susceptible to collapse after multiple fires. With fewer survivors, it becomes increasingly harder for species to reestablish themselves in burned areas.

The specter of such a future underlines the urgency of better protecting vulnerable species and ecosystems. To inform that work, all of the scientists interviewed want to see dedicated on-the-ground studies after the fires subside. Stawski and Doty have also advocated for more work to understand the physiological impacts of fire on individual animals, such as changes to metabolism or the effects of smoke exposure. “There’s so little research that’s been done, it stresses me out,” says Doty, who will study smoke impacts on bats this summer in California.

She and others say such work will help build a more complete picture of wildfire impacts and will better inform the conservation measures needed to prevent the appalling scenes of recent weeks from becoming the new normal—and an existential threat to Australia’s biological bounty. Stawski, for one, says she has hope but that right now “it’s very hard to watch what’s happening.”