The bush fires raging in Australia have likely killed or injured thousands of koalas, further stressing the national icon's fragile population, wildlife experts said Friday.

Koala populations already are threatened by human development. Many of those populations will be diminished drastically by the fires burning across New South Wales state and may not rebuild for 15 years, the National Parks and Wildlife Service said.

"Koalas are vulnerable. They are slow moving," service director Brian Gilligan said. "No doubt many thousands of koalas have either been killed or injured in the fires."

Eucalyptus trees have a high oil content and are extremely combustible. Often, the wildfires engulf a tree before koalas have the chance to escape.

"What they would do is climb to the tops of trees and tuck themselves into a ball, covering their sensitive parts such as their nose, ears and eyes," said John Callaghan, chief ecologist of the Australian Koala Foundation.

"If they manage to survive by doing this, they still often end up with severe burns and respiratory problems."

Koala population numbers have been cut by the destruction of forests. Until they were formally granted protection in the 1930s, millions were shot by hunters for their soft fur.

Although not officially listed as an endangered species, koalas are regarded by wildlife experts as threatened.

The Australian Koala Foundation, which wants greater protection for the species, estimates the national koala population at fewer than 100,000.

The latest fires sweeping Australia could affect the koala's ultimate survival.

Close to 1.2 million acres of land, most of it eucalyptus forests where koalas thrive, have been razed in the "black Christmas" fires. About half of the 100 fires were deliberately set, officials said.

Firefighters got a break Saturday as temperatures dropped to 79 degrees after hitting 100 earlier this week. Humidity also rose after a string of dry days. But forecasters said temperatures were expected to soar soon with a return of dry Outback winds, restoring conditions that have fanned the fires.

The biggest fire was raging through a national park near the tiny town of Colo Heights, 37 miles northwest of Sydney.

Cameron Wade of the New South Wales Rural Fire Service said it had jumped a highway and was heading into rugged bushland, inaccessible to fire crews.

"It is just monstrous in size. I don't have the figures. But looking at it on the map it takes up a huge amount of space," he said.

Residents there were being ordered to leave their homes as a precaution amid fears that the fire might join up with several others burning nearby.

Another large fire was in the Blue Mountains, 50 miles west of Sydney, threatening houses and roaring up steep hillsides and gullies.

No human lives have been lost since the fires began 12 days ago, but almost 170 homes have been destroyed and thousands of people have been evacuated.

Koalas, along with many other native creatures, have not been so lucky.

Those that survive the initial fire face starvation. It takes several weeks, even months, before their food source regenerates, Callaghan said.

Koalas are highly territorial and loath to move, even if their own habitat is destroyed by fire. If they do relocate, they face fierce confrontations with other koalas.

Despite their cute and cuddly image, wild koalas will bite, scratch and claw.

In some areas, koalas have been given a fighting chance. Some new suburbs have been built with special corridors of trees and scrub that give koalas an escape route to other areas.

"If koalas become completely isolated and you get some catastrophic event such as a fire, it can just go through and wipe them out," said Larry Vogelnest, senior veterinarian at Sydney's Taronga Zoo. "These corridors are critical for the migration of animals in and out of these pockets."