WATERHOLES, AUSTRALIA—The convoy of vehicles fleeing a raging inferno in the forest of southeastern Australia ferried a copious cargo: 11 koalas, 15 kangaroos, five chickens, two possums, two dogs and a lorikeet.

Susan Pulis, who runs a wildlife shelter, had rallied her friends to pack the animals in blankets and baskets and take them to safety on the coast. One friend gutted her downstairs bedroom to house five of the kangaroos. Pulis has kept the youngest joeys in quilt pouches in another’s living room.

“Since the fires, they are very different,” she said of the animals, “very on edge.”

As wildfires have killed at least 24 people, destroyed more than 1,400 homes and ravaged over 6 million hectares, they have also inflicted a grievous toll on Australia’s renowned wildlife. Hundreds of millions of animals, many found on no other continent, may have perished, according to some estimates, devastating the country’s unique ecosystems.

“We will have taken many species that weren’t threatened close to extinction, if not to extinction,” said Kingsley Dixon, an ecologist and botanist at Curtin University, in Perth.

Even the animals that survived, scampering away or hunkering down, may die from dehydration or starvation, Dixon added. “It’s a biological Armageddon rarely seen,” he said.

Wildlife in Australia was already under threat before these fires, as humans have changed the landscape. Agribusiness is among the top contributors to deforestation, which decimates wildlife populations, scientists say.

The astronomical estimates of animal losses and the heart-rending images of singed koalas during this disastrous fire season have spread the concern worldwide. Quilters in the Netherlands have made mittens for koalas with burned paws. New Zealanders are stitching joey pouches and bat wraps.

Some experts have been dubious of the high numbers that have spread widely on social media, which are based on estimates of population densities of mammals, birds and reptiles from previously published studies. The death toll is arrived at by multiplying the number of animals expected to inhabit a given area by the total acreage burned.

But it is impossible to know how many animals managed to flee, for instance. Limited access to the burned lands, as well as the difficulty of documenting individual animal deaths, complicate efforts to assess the scale of the damage.

Whatever the numbers, it is clear that the devastation is immense, scientists say.

“It’s dangerous to put a number to them,” said Corey Bradshaw, a fellow in ecology at Flinders University in Adelaide, in the south. But, he added, “there’s no question there has been deaths.”

At least a quarter of the koala population may have been lost in New South Wales, according to various estimates. Significant numbers of the southern brown bandicoot and the long-footed potoroo, a kind of wallaby whose entire habitat has been ravaged by fire, have also most likely been lost.

On Kangaroo Island, off the coast of South Australia, experts said thousands of kangaroos and koalas had been killed in the fire that has now ravaged a third of the island. There are also grave fears for the fate of a subspecies of glossy black cockatoos, of which there were only about 300 to 370 remaining before the fires.

It is not only wildlife that has been ravaged. In Batlow, 458 kilometres southwest of Sydney, a video taken by a reporter showed the scorched corpses of sheep and cows strewn along a highway. Carcasses like these have raised biological fears around the country.

Buchan, a farming region in the southern state of Victoria, has also been badly affected, with farmers having to put down burned livestock at a time when drought had already made earning a living nearly impossible. Farmers in the nearby town of Bairnsdale said that a cattle sale was planned Thursday to unload their remaining livestock, some of which may be injured.

Tina Moon, a farmer in Sarsfield, a town in Victoria’s southeast, said many burned cattle in the region had to be euthanized. She said she had saved her house, but had no idea how she would make an income in the coming months.

To protect Australia’s wildlife, rescuers like Pulis, who fled the forest for the coast late last month, are battling immense changes to the country’s landscape on a tiny scale. They cannot save Australia’s wildlife on their own, but their work is reinforcing scientists’ judgment that intervention will be increasingly necessary to protect animals on a hotter, more fiery planet.

Around the country, people have banded together to help feed, find and rehabilitate survivors.

In the fire-ravaged town of Mallacoota, one man says he has rescued nine koalas, for which the community is working to build a shelter. Others have left out seed, water and grasses for dehydrated and hungry fauna.

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“I know it doesn’t bring back properties, but for some it can give a sense of not giving up the fight,” said Katharine Catelotti, of Sydney, whose family lost a small shack in Wollomombi, more than 482 kilometres north of the city, and has been putting feed out for wildlife as well as keeping a small number in her home.

The task for others has been more grim. One woman told the Australian Broadcasting Corp. that she was checking the pouches of dead kangaroos for joeys and marking the ones without them so that other searchers would not have to repeat her efforts.

For Pulis, evacuating her few animals — which had already been rescued, some of them more than once, from starvation, dog attacks and car accidents — was simply part of life.

In 2013, she founded a wildlife shelter on Raymond Island, a town just off the coast, with the intention of rehabilitating injured and abandoned creatures. In August, she relocated to Waterholes, 48 kilometres inland, because of the clearing of the island’s trees, which had made it impossible for her to release the koalas into an environment where they could find sufficient food.

Somehow, her property in Waterholes, threatened twice by fires this season, remains standing, a lush oasis at the end of a blackened road in the eastern Victoria region of East Gippsland, where smouldering and fallen trees, charred earth and melted road signs stretch for hundreds of miles.

“It’s a holocaust,” Pulis said as she drove toward her home Monday for the first time since blistering heat brought through a ferocious fire front.

Cool weather and rain have since brought a reprieve. But smoke still hung in the air. As she reached the track leading to her property, Pulis began to cry.

“This was my koala feed,” she said of the scorched eucalyptus trees, which used to provide leaves for her animals. “It was absolutely alive.”

At her property, Pulis tended to the stressed and dehydrated kangaroos she had been forced to leave behind. She gave each an injection to relieve their pain — they had most likely hopped so frantically away from the burning forest that they had injured themselves — and refreshed their water, which was contaminated by ash.

On Saturday, as yards-high flames threatened her property for a second time, Pulis’ friend Jason Nicholson defended it with a hose and hundreds of gallons of water.

Neither could believe that it remained intact — the garden surrounding it still green, with cockatoos calling from the trees. They said they expected that wildlife, pushed out by the fires, would congregate in what was now a garden of Eden among miles of decimated forest.

“The difference is here, you hear the birds,” Nicholson said. “Out there, it’s quiet. Deadly quiet.”

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