Like a Bird on a Wire That Starts a Wildfire

A variety of triggers can kindle wildfires on dry lands: high winds that send power lines careening into each other, stray cigarette butts, even sparks from train wheels. And, sometimes, electrocuted birds.

In 2017, a hawk carrying a snake lit a 40-acre blaze in Montana. The accidental arsonist was found crisped on the ground, its well-done dinner still grasped in its talons. The snake-hawk duo might have touched two power lines at once, forming a circuit that electrocuted both before they fell and ignited the grass. That was one of at least 44 wildfires caused by electrocuted birds in the United States from 2014 through 2018, researchers reported this month in the Wildlife Society Bulletin. Anecdotes of blazes caused by birds pop up occasionally, and researchers are still working to understand how much of a wildfire risk really results from such fowl play.

Such electrocutions typically occur in places with few trees, where bigger bird species may perch or nest on utility poles, said Taylor Barnes, a geospatial information system specialist at E.D.M. International, a consulting company for electric utilities, and one of the authors of the paper. A bird can rest on one wire with no problem. But touching two wires simultaneously or touching one wire and a piece of grounded equipment, such as a transformer, can cause trouble.

“When electrocutions happen, it’s not unusual for the water in the animal cells to be instantly turned to steam,” said James Dwyer, a wildlife biologist also at E.D.M. International and a co-author of the paper. “It explodes the cells, and it’ll blow off a limb.”

Sometimes, the bird’s plumage ignites, and it may be left suffering on the ground.

“It’s a really rough way to go if it doesn’t happen instantly,” he said.

There is no database of bird-caused blazes, so the researchers scoured news reports for combinations of words such as “fire” and “eagle,” keeping those that included photographic evidence of charred birds or comments from firefighters or utility workers.

Most of the fires that the team found were small — less than five hectares, or about 12 acres, the size of a few city blocks. But one caused by a raptor in 2015 burned 10,000 acres in Idaho. Incendiary avians included eagles, hawks and turkey vultures, but in many cases, the type of bird was not reported.

Mapping these burns against ecoregions — areas defined by their similar ecosystems and environmental resources — revealed that the Mediterranean California region, much of the western part of the state, had the greatest number of bird fires, despite it being the smallest area.

The higher density of fires in the region caused by bird electrocutions may result from heavy spring rains, which spur the rapid growth of vegetation. Summer heat then follows, which dries all that new growth, creating fuel for fires that is relatively easy to ignite, Dr. Dwyer said. There may also be a greater density of electrical infrastructure, such as utility poles where birds can be electrocuted.

Overall, the density of wildfires caused by bird electrocutions was minuscule compared with the total density of wildfires in all the regions. “We’re not talking about a lot of ignitions,” said Jon Keeley, a fire ecologist with the U.S. Geological Survey at Sequoia National Park in California who was not part of this study. The vast majority of wildfires are caused by humans, and this is another example of that, he said. “It’s something that’s caused by human infrastructure.”

Power lines pose threats to birds all over the world, including threatened raptors wintering in North Africa and migrating birds passing through China, said José Rafael Garrido López, a wildlife biologist for the Environmental and Water Agency of Andalusia in Spain who also was not involved with this study. By one estimate, around 10 million birds may die by electrocution each year in the United States alone, and even more die from collisions with electrical infrastructure.

Occasionally, a rare bird-caused inferno leads to human deaths, too. A 2014 fire in Valparaíso, Chile, burned thousands of homes and killed 15 people. A 10-month investigation turned up electrocuted birds.

To lower the risks of wildfires caused by birds, utilities companies can cover wires on the poles with plastic insulators to keep birds from frying themselves. It’s a simple solution, and some electric utilities companies throughout the United States are working to mitigate avian electrocutions and fire risk, Dr. Dwyer said. In some places, conservationists have also tried placing nesting boxes atop utility poles to keep birds from nesting near metal wires or other equipment.

“The cost of mitigation is far less than the potential consequence of these fires,” whether loss of human life, loss of wildlife habitat or damage to electrical infrastructure, Mr. Barnes said.