Australia's unprecedented wildfires season has so far charred 40,000 square miles (104,000 square kilometers) of brushland, rainforests, and national parks — killing by one estimate more than a billion wild animals. Scientists fear some of the island continent's unique and colorful species may not recover. For others, they are trying to throw lifelines.

Where flames have subsided, biologists are starting to look for survivors, hoping they may find enough left of some rare and endangered species to rebuild populations. It's a grim task for a nation that prides itself on its diverse wildlife, including creatures found nowhere else on the planet such as koalas, kangaroos and wallabies.

"I don't think we've seen a single event in Australia that has destroyed so much habita t and pushed so many creatures to the very brink of extinction," said Kingsley Dixon, an ecologist at Curtin University in Perth.

Not long after wildfires passed through Oxley Wild Rivers National Park in New South Wales, ecologist Guy Ballard set out looking for brush-tailed rock wallabies.

The small marsupials resemble miniature kangaroos with long floppy tails and often bound between large boulders, their preferred hiding spots.

Before this fire season, scientists estimated there were as few as 15,000 left in the wild. Now recent fires in a region already stricken by drought have burned through some of their last habitat, and the species is in jeopardy of disappearing, Ballard said.

In prior years, his team identified a handful of colonies within the national park. After the recent fires, they found smoking tree stumps and dead animals.

"It was just devastating," said Ballard from the University of New England in Armidale. "You could smell dead animals in the rocks."

But some wallabies, his team discovered, were still alive. "All you can do is focus on the survivors," he said.

Australia's forests and wildlife evolved alongside periodic wildfires. What's different this year is the vast extent of land burned — an area as big as Kentucky — against a backdrop of drought and searing temperatures attributed to climate change.  Last year, among the driest in more than a century, saw temperatures that routinely topped 104 degrees Fahrenheit (40 degrees Celsius).

Not all animals will perish in the blazes. Some can shelter in rock crevices or hide deep in underground burrows. Yet when survivors emerge into a fire-scorched wasteland, they will face hunger, thirst and non-native predators, including introduced foxes and feral cats.

Since fires swept through parts of Oxley Wild Rivers National Park nearly two months ago, there's been little rain and no green shoots.

So Ballard's team has trekked through the ash-covered forest carrying water and sacks of sweet potatoes, carrots and food pellets.

"There are so few left that, with a species this rare, every individual counts," he says.

Elsewhere in New South Wales, conservation workers are dropping vegetables from airplanes into scorched forests, hoping that wallabies and other species find a meal.

In the state of Victoria, authorities estimate that brush-tailed rock wallabies lost 40% of their habitat as did another rare marsupial, the long-footed potoroo, according to a preliminary damage assessment.

The full toll on Australia's wildlife includes at least 20 and possibly as many as 100 threatened species pushed closer to extinction, according to scientists from several Australian universities.

"The worry is that with so much lost, there won't be a pool of rare animals and plants to later repopulate burnt areas," said Jim Radford, an ecologist at La Trobe University in Melbourne.

The fires could knock out rainforest species dating back to the time of the Gondwana supercontinent, before the modern continents split apart, he said.

University of Sydney ecologist Christopher Dickman estimated that more than 1 billion animals have been killed so far. His calculations took previously-published animal density numbers for different vegetation types and multiplied that by acreage burned.

He says that number does not include bats, amphibians, insects or other invertebrates.

The wildlife toll includes tens of millions of possums and small marsupials known as gliders, which live in tree tops and can leap extraordinary distances by using a parachute-like membrane of skin between their ankles and wrists. State officials in Victoria predicted more than a 25% reduction in glider numbers from the fires.

"The implications for some species are pretty grim," Dickman said. "If we can't protect them here, they're gone. No one else has them."

The Australian government announced Monday that it was spending $50 million on emergency wildlife rescue efforts and habitat recovery.

Fires are still burning in the Blue Mountains, a UNESCO World Heritage site west of Sydney — one of the last strongholds of the regent honeyeater, an elegant black and yellow bird that has already lost 95% of its breeding habitat since European settlers arrived in Australia.

There are only 300 to 400 of the birds left in the wild, says Ross Crates, an ecologist at Australia National University. They are dependent on nectar from certain eucalyptus tree blossoms, but the dry weather has meant that many trees are producing no nectar.

After the wildfires subside, Crates plans to survey what's been newly scorched. "Even for birds that survive the fires, we are concerned about how they will feed and nest."

In recent months, areas that don't usually burn went up in flames. Some rainforests dried up in the drought and extreme heat, allowing fire to sweep through them.

Few images have tugged at heartstrings more than koalas clinging to burnt trees. Unlike birds or ground mammals, they cannot fly away or burrow underground.

While koalas are not classified as vulnerable to extinction, their  populations in some fire-ravaged areas may have been snuffed out. "We know there's been a massive reduction of their overall habitat, and we're not even at the end of fire season," said Mathew Crowther, an ecologist at the University of Sydney.

"Koalas won't go extinct in the next few years, but if their habitat is destroyed bit by bit, it could eventually be death by a thousand cuts. We have to look at long-term trends — what will the temperatures and wildfires be like in the future?"

Firefighters in Australia have succeeded in protecting an extremely rare grove of ancient trees from destruction, with specialist teams going to extreme measures as bushfires closed in, authorities confirmed on Wednesday.

The Wollemi Pines in the Blue Mountains of New South Wales (NSW) state are the only known members of their species in the world and are sometimes called the "dinosaur trees" due to their prehistoric origin.

"Wollemi National Park is the only place in the world where these trees are found in the wild and, with less than 200 left, we knew we needed to do everything we could to save them," NSW Environment Minister Matt Kean said.

As the fire front approached the trees' confidential location, firefighters doused water and flame retardant from the land and sky, creating a barrier and subverting their destruction.

As well as aerial water-bombing jets, firefighting specialists dropped into the location by helicopter to create a makeshift irrigation system powered by a generator.

While parts of the trees were charred and the surrounding bushland levelled, the Wollemi Pines survived largely unscathed as the fire front passed through the area.

The unique trees were thought to be extinct, until they were accidentally discovered thriving in the Australian wilderness in 1994.

Kean said that the latest operation would act as a lesson for future conservation efforts.

"The 2019 wildfire is the first ever opportunity to see the fire response of mature Wollemi Pine in a natural setting, which will help us refine the way we manage fire in these sites long-term," he said.

"Illegal visitation remains a significant threat to the Wollemi Pines survival in the wild due to the risk of trampling regenerating plants and introducing diseases which could devastate the remaining populations and their recovery."

Fire alarms have been sounding in high-rise buildings across downtown Sydney and Melbourne as dense smoke from distant wildfires confuse electronic sensors. Modern government office blocks in the Australian capital Canberra have been closed because the air inside is too dangerous for civil servants to breathe.

The sun has glowed an eerie red behind a brown shrouded sky for weeks over Australian metropolitan areas that usually rank high in the world's most livable cities indexes.

It's an unprecedented dilemma for Australians accustomed to blue skies and sunny days that has raised fears for the long-term health consequences if prolonged exposure to choking smoke becomes the new summer norm. Similar concerns over smoke are emerging in other regions of the globe being impacted by more fires tied to climate change, including the Western U.S.

"I'm going to give birth any day now, literally, and I'm going to have a newborn baby that I'm going to protect from all this," said Emma Mauch, a pregnant Canberra mother.

Her friend, Sonia Connor, described the struggle of keeping her own energetic 3-year-old daughter contained inside their Canberra house with windows and doors sealed by tape as the outside temperature exceeded 42 degrees Celsius (108 degrees Fahrenheit). It's a choice between air flow in stifling heat or keeping potentially toxic smoke out.

"My daughter hasn't shown any sort of symptoms, let's say. For me, I can feel it in my lungs, my throat has felt weird," Connor said.

"It doesn't seem to be stopping her, but the long-term effects? Who knows? She's 3. Who knows what's going to happen?" she added.

Slovenian tennis player Dalila Jakupovic fell to her knees in a coughing fit on Wednesday while competing in a qualifying match for the Australian Open in Melbourne.

"I've never experienced something like this," Jakupovic told Australian Broadcasting Corp.

"We are used to pollution — like, we play in China and more polluted countries — but this smoke is something different that for sure we're not used to."

Canberra as well as Australia's two largest cities, Sydney and Melbourne, have at various times in recent weeks rated as the most polluted cities in the world, although some argue the industrial pollutants in places such as New Delhi are more dangerous than wood smoke.

The fires have claimed at least 27 lives since September, destroyed more than 2,600 homes and razed more than 10.3 million hectares (25.5 million acres), mostly in New South Wales state. The area burned is larger than the U.S. state of Indiana.

Hospital admissions have increased in the smoke-affected cities, with some patients suffering asthma for the first time in their lives. The government has responded by distributing 3.5 million free particle-excluding masks.

Acting Australian Chief Medical Officer Paul Kelly said he was discussing with the government launching a study of the long-term health implications of the wildfire smoke.

Bruce Thompson, president of the Thoracic Society of Australia and New Zealand, is among the respiratory disease experts who predict increases in heart and lung diseases as well as some cancers if climate change makes prolonged exposure to wildfire smoke an annual phenomenon.

"We're breathing in stuff that the lungs don't like that leads to significant changes, especially people who are predisposed to respiratory conditions," Thompson said.

Thompson, who suffers itchy eyes and a running nose from smoke at home in Melbourne, said comparisons could be drawn between the current crisis and a wildfire that ignited coal in the open-cut Hazelwood mine near the town of Morwell in Victoria state in 2014. The fire burned for 45 days, blanketing Morwell and its 14,000 residents in thick smoke and coal dust.

That exposure was still taking tolls on the health of the Morwell community and the wider Latrobe Valley, particularly the young, Thompson said.

Brian Oliver, head of the Respiratory Molecular Pathogenesis at University of Technology Sydney, likened prolonged and repeated exposure to such wildfire smoke to smoking cigarettes.

Oliver predicted increases in smoker diseases across Australia if the wildfire smoke became more common in a drier and hotter future.

NASA says the unprecedented masses of Australian smoke that have drifted east across the Pacific Ocean have returned after circumnavigating the globe.

In the U.S., an estimated 20,000 premature deaths now occur annually due to chronic wildfire smoke exposure. That's expected to double by the end of the century, according to scientists funded by NASA, as tens of millions of people get exposed to massive "smoke waves" emanating from blazes in Western states.

Experts say an increase in serious health problems in California may be almost inevitable for vulnerable residents as the disasters become more commonplace.

Research suggests children, the elderly and those with existing health problems are most at risk.

Short-term exposure to wildfire smoke can worsen existing asthma and lung disease, leading to emergency room treatment or hospitalization, studies have shown. Increases in doctor visits or hospital treatment for respiratory infections, bronchitis and pneumonia in otherwise healthy people also have been found during and after wildfires.

Some studies also have found increases in ER visits for heart attacks and strokes in people with existing heart disease on heavy smoke days during previous California wildfires, echoing research on potential risks from urban air pollution.

For most healthy people, exposure to wildfire smoke is just an annoyance, causing burning eyes, scratchy throats or chest discomfort that all disappear when the smoke clears.

Wood smoke contains some of the same toxic chemicals as urban air pollution, along with tiny particles of vapor and soot 30 times thinner than a human hair. These can infiltrate the bloodstream, potentially causing inflammation and blood vessel damage even in healthy people, research on urban air pollution has shown. Studies have linked heart attacks and cancer with long-term exposure to air pollution.

Whether exposure to wildfire smoke carries the same risks is uncertain, and determining harm from smog versus wildfire smoke can be tricky. There is little known about the long-term effects of wildfire smoke because of difficulties in studying populations years after a wildfire.

Michael Abramson, professor of epidemiology and preventive medicine at Melbourne's Monash University, is a co-author of a report on the ongoing investigation of the health impacts of the Hazelwood blaze.

Abramson urges a national study of the health impacts of the latest wildfires, saying his research focused on a much smaller population of 74,000 people in the Latrobe Valley.

"We're now seeing substantial exposure extending over weeks to cities that have millions of inhabitants, so I think it's very likely that there might be more subtle effects that we haven't been able to detect," Abramson said.

The political party Australian Greens called on the government to establish a climate emergency national medical stockpile to prepare for future bushfire crises.

Richard Di Natale, the leader of the Greens, said that under his plan the stockpile would include smoke-filtering masks.

The air quality in Melbourne on Tuesday morning dropped to hazardous levels, as smoke from Victoria's northeast fires blanketed the state.

"It's almost impossible to avoid. It can claim lives, and it hurts everyone's quality of life," Di Natale said, according to The Sydney Morning Herald report on Monday evening.

"Already one person has died in Canberra, and the public health impacts on the broader population won't be known for months."

The government has an existing stockpile with 1.8 million masks available, but the Greens demanded a significant expansion.

Retailers across the country have sold out of P2 masks, which filter out hazardous smoke particles, forcing them to order hundreds of thousands more.

Wesfarmers, the owner of hardware giant Bunnings, earlier in January said that demand for the masks was "through the roof."

"The Australian Greens are launching the climate emergency national medical stockpile to reflect the immediate risk to people's health," the Greens said in a statement.

"It will give people an assurance that their government has the ability to respond to the health impacts of the fire crises, without running into the widespread mask shortages we have seen since December."

Greg Hunt, minister for health, has promised that the government will make more masks available as demand rises.

Crews battling Australia's wildfires said Sunday that they have been able to turn from defense to offense for the first time in weeks thanks to a break in the weather.

Dale McLean, who is helping manage the response to a fire near the town of Bodalla in  New South Wales state , was part of team that was bulldozing down small trees and burning scrub ahead of the fire's projected path to try to stop it from reaching a major highway by starving it of fuel.

"This fire took a major run about seven or eight days ago, and with the weather changing now, the weather settling down, the fire has settled down," he said. "The fire behavior has changed. So we're able to get in front of the fire now, get on the offensive."

Other workers echoed McLean's comments, saying cooler temperatures and mild winds have finally offered them a chance to make progress. The weather is expected to remain benign for the next week, although any deterioration in conditions after that could see the wildfires flare up again.

The progress came after a firefighter was killed by a falling tree. Bill Slade — one of the few professionals among mainly volunteer brigades battling blazes across southeast Australia — died on Saturday near Omeo in eastern Victoria state, Forest Fire Management Victoria Executive Director Chris Hardman said.

The 60-year-old married father of two was commended in November for 40 years of service with the forestry agency.

"Although we do have enormous experience in identifying hazardous trees, sometimes these tree failures can't be predicted," Hardman said. "Working on the fire ground in a forest environment is a dynamic, high-risk environment and it carries with it significant risk."

The tragedy brings the death toll to at least 27 in a crisis that has destroyed more than 2,000 homes and scorched an area larger than the U.S. state of Indiana since September. Four of the casualties have been firefighters.

The crisis has brought accusations that Prime Minister Scott Morrison's conservative government needs to take more action to counter climate change, which experts say has worsened the blazes. Thousands of protesters rallied Friday in Sydney and Melbourne, calling for Morrison to be fired and for Australia to take tougher action on global warming.

The prime minister said Sunday that his government was building resilience to the fire danger posed by climate change.

He said the government was developing a national disaster risk reduction framework within the Department of Home Affairs that will deal with wildfires, cyclones, floods and drought.

"This is a longer-term risk framework model which deals with one of the big issues in response to the climate changing," Morrison said.

He said his government accepted that climate change was leading to longer, hotter and drier summers, despite junior government lawmaker George Christensen posting on social media over the weekend that the cause of the latest fires was arson rather than man-made climate change. Another junior lawmaker, Craig Kelly, has also publicly denied any link between climate change and fire crisis.

State authorities have said a minority of fires are deliberately lit.

"The government's policy is set by the Cabinet. Our party room has a broad range of views," Morrison said of those within government ranks who reject mainstream climate science.

Morrison also announced that 76 million Australian dollars ($52 million) would be spent on providing psychological counseling for firefighters and fire-affected communities as part of a previously announced AU$2 billion ($1.4 billion) recovery fund.

"There has been a deep scar in the landscape that has been left right across our country," Morrison said. "But I am also very mindful, as is the government, of the very real scars that will be there for quite a period of time to come for those who've been exposed to the trauma of these bushfires."

While the fire threat is most acute in rural communities, wildfire smoke that has choked some of Australia's largest cities is a reminder to many urban Australians of the unfolding disaster.