How Koalas Survive Forest Fires: Australia Is Global Test for Animals

“You’d think we’d know a bit more about how animals like the koala deal with fire,” said

Kara Youngentob,

a research fellow at Australian National University who is investigating what koalas can eat in a recently burned forest. “It’s amazing what we still don’t know about them in a country where fire does occur regularly.”

Many animals have strategies for dealing with fires, and some plants even require heat from the flames to germinate their seeds. But scientists worry the trend toward bigger and more destructive fires—partly because of climate change—poses a significant risk even for fire-adapted species. In California, where firefighters have battled huge wildfires, one study showed that the annual area burned had quintupled over recent decades.

The results from Dr. Youngentob and other scientists across Australia could inform policy on how best to help struggling wildlife. Already, a government panel of wildlife experts has identified 119 animal species, including ground-dwelling parrots and rat-like marsupials called potoroos, which have been threatened most by the fires. Koalas, also on the list, were already declining in numbers because of habitat loss from land clearing, logging and development.

Australia’s government is spending roughly $148 million to help native wildlife and their habitats recover. Still, conservation groups have criticized conservative Prime Minister Scott Morrison for attempting to weaken environmental-protection laws. Mr. Morrison contends he is trying to make regulations more efficient.

At a wildlife sanctuary south of Canberra, Australia’s capital, Dr. Youngentob and others recently released four koalas that had been rescued after the fires. The animals were let loose where they were found—an area where the foliage has started to recover—though parts of the sanctuary still don’t have new growth.

“One of the koalas, she climbed up and then just stayed in a branch and immediately started eating,” said

Karen Ford,

another research fellow at ANU who is coleading the research with Dr. Youngentob. “She seemed totally unconcerned with everyone watching her.”

The scientists have used thermal drones, which can detect the heat signature of koalas in a forest, to find animals living in burned areas that were never rescued. By tracking those koalas, they can learn how the animals adapt to the post-fire landscape and how they fare compared with others living in a nearby area that didn’t burn. The recently released koalas are being monitored as a third group.

Dr. Youngentob said it isn’t known to what extent koalas can eat leaf shoots that appear as trees regenerate after fires. Sometimes, trees will protect new growth by making them more toxic than adult leaves. An initial experiment found that of tree species whose adult leaves koalas eat, only about half have leaf shoots the koalas eat. The animals, however, also ate some leaf shoots from trees they normally avoid.

Reid Tingley,

an ecologist at Monash University, is leading an effort to filter DNA from water samples to determine which animals are present nearby. One priority is to track the platypus, an elusive water-dwelling animal that has fur like other mammals but also has a beak and lays eggs.

Dr. Tingley was working on a similar study before the fires. His team is sampling the same areas to learn whether the range of the platypus has changed. Among other things, he is concerned that rain could have washed ash into waterways, lowering the water quality and killing off invertebrates that the platypus eats. Vegetation on riverbanks also provides shade and regulates water temperature, but that burned away completely in some areas.

“It’s a question of whether they can cope with the type of fires that we just saw,” Dr. Tingley said.

Key for animal survivors is how quickly flora can regrow and provide a stable food source. Some trees can begin sprouting new leaves within weeks, and a 2016 study using satellite imagery of burned areas near Sydney found that a forest could have fully regenerated within five to seven years. But much depends on the forest’s condition before the blaze and how often it burns.

“If a system is burned repeatedly, you can start to have resprouting failure,” said David Lindenmayer, a professor and ecologist at ANU. If young forests are often ravaged by fire, it will be difficult for big trees to grow, he added.

At Kangaroo Island, off southern Australia’s coast, researchers using motion-sensor cameras were surprised to find dunnarts, a small carnivorous marsupial, in the burned bush. Nearly half the island burned in the most recent fire season, threatening the estimated 300 to 500 dunnarts there.

Pat Hodgens, an ecologist working for Kangaroo Island Land for Wildlife, a nonprofit, said the dunnarts could have escaped the fires in underground burrows. Researchers are now planning to use radio tags to track dunnarts in burned and nonburned areas to learn more about how they survive.

“How these little animals managed to navigate life and survive in that moonscape is what absolutely amazes me,” Mr. Hodgens said. “We can only hazard a guess.”

Write to Mike Cherney at mike.cherney@wsj.com