What do wild animals do in wildfires?

Wildfires are raging across California, as the state faces a record-breaking fire season due to the destructive combination of a heat wave and strong winds. Blazes have burned more than two million acres of land—the most on record for a single wildfire season—and destroyed more than 3,300 structures so far. Meanwhile, warnings for severe fire danger have been issued across the West Coast of the United States, including in Oregon and Washington State.

It’s unclear how many animals have died—such data is not tracked consistently across regions—but it’s clear that even species that have evolved to thrive in habitats that burn regularly are facing new challenges.

Escape or hide

“Wildlife have a long-standing relationship with fire,” ecosystem ecologist Mazeika Sullivan of the Ohio State University said in a 2014 interview. “Fire is a natural part of these landscapes.”

Many species actually require fire. Heat from the flames can stimulate some fungi, like morel mushrooms, to release spores. Certain plants will seed only after a blaze. And some animals, such as mule deer and black-backed woodpeckers, require burned areas to both eat and nest. Without fire, those organisms can't reproduce—and anything that depends on them will be affected. (Related: Find out why these birds carry flames in their beaks.)

Forest animals typically have some ability to escape the heat. Birds may fly away, mammals can run, and amphibians and other small creatures burrow into the ground, hide out in logs, or take cover under rocks. And other animals, including large ones like elk, will take refuge in streams and lakes.

Nonetheless, the intensity of today’s wildfires is something even many fire-adapted species aren’t able to cope with.

Fire seasons are growing longer, and fires are burning hotter, spread faster, and lasting longer. Since the early 1970s, the wildfire season in the western U.S. has grown from about five to more than seven months. As climate change drives up temperatures and worsens drought conditions, landscapes are becoming increasingly dry and more susceptible to burning.

More than a century of attempts to suppress wildfires means that when they do break out, they burn hotter and faster. Originally adapted to routine, natural fires, many forests now contain swaths of unburned trees and vegetation that provide fuel for severe, long-lasting blazes. Researchers worry that these increasingly frequent wildfires will negatively affect even fire-adapted species, such as the black-backed woodpecker, which needs both burned and unburned habitat to thrive.

‘Winners and losers’

Gabriel d'Eustachio, a bush firefighter in Australia, said in 2014 that he has witnessed mass movements of small invertebrates fleeing blazes. “You get overrun by this wave of creepy crawlies walking ahead of the fire,” he said. (Find out what it's like to be on the front line of the fight against wildfires.)

Fires can benefit predators that prey on these fleeing animals. Bears, raccoons, and raptors, for instance, have been seen hunting creatures trying to escape the flames. Several species of birds may even help spread fires in Australia, some research suggests, as doing so may help flush out small animals for them to eat.

“In those short-term situations,” such as when creatures flee from flames, says Sullivan, “there’s always winners and losers.”

A moderate level of fire in areas where it naturally occurs may also increase the “patchiness” of forests and create a wider variety of microhabitats, from open meadows to re-growing forest, research shows. Having a diversity of biomes supports multiple species of animals and the ecosystem as a whole.

Scientists don't have any good estimates on the number of animals that die in wildfires each year. But there are no documented cases of fires—even the really severe ones—wiping out entire populations or species. (Watch: “Fish skin bandages help burned bears and cougar heal”)

Of course, some animals do die in the smoke and fire—those that can't run fast enough or find shelter. Young and small animals are particularly at risk. And some of their strategies for escape might not work—a koala’s natural instinct to crawl up into a tree, for example, may leave it trapped.

Heat can kill too—even organisms buried deep in the ground, such as fungi. Jane Smith, a mycologist with the U.S. Forest Service in Corvallis, Oregon, has measured temperatures as high as 1,292 degrees Fahrenheit beneath logs burning in a wildfire, and 212 degrees Fahrenheit a full two inches below the surface.

Change agents

Wild areas like forests and prairies naturally grow and change in composition over time. A year-old forest will have a different set of plants and animals living in it than a forest that’s 40 years old. A disturbance like a wildfire can serve as a reset button, letting an old forest be born again, said Patricia Kennedy, a wildlife biologist at Oregon State University in 2014. And “a lot of species require that reset.”

Exactly what happens after a fire occurs depends on the landscape, the severity of the fire, and the species involved. But the event always sparks a succession of changes as plants, microbes, fungi, and other organisms recolonize the burned land. As trees and plants age, light and other features change—and the composition of creatures in the area changes in response.

Streams and other water bodies that flow through a burned area can also change. Water flow, turbidity, chemistry, and structure can be altered. Fish may temporarily move away. And there can be short-term die-offs among aquatic invertebrates, which can affect animals on land.

“The water and the land are highly connected,” Sullivan says.