Electrocuted, flaming bird carcasses are falling off of power lines and causing wildfires across the U.S. This surprisingly common phenomenon has been responsible for at least three Colorado wildfires so far this summer.

These events are not isolated. A 2022 study found that electrocuted birds caused 44 wildfires in the contiguous United States between 2014 and 2018. That study was led by Taylor Barnes, a biologist who now works for electric utility company EDM International. In the paper, Barnes wrote that “avian-caused ignitions” happen when a bird sits on an overhead power line. For reasons that can vary from case to case, sometimes the bird receives a powerful electrical shock, setting its feathers on fire. The dead or dying bird then falls, and, on occasion, lands in some brush or other flammable material.

“Sometimes they burst into flames,” Barnes told 9News, an NBC affiliate in Colorado. “Sometimes they just fall dead. Not every bird that is electrocuted will fall to the ground and start a fire.”

Odds are, you’ve seen birds perched on electrical wires countless times without witnessing spontaneous sparrow combustion. Barnes said birds just going for a sit pose no threat. Because the birds are not touching the ground, the electricity in the power line has no way to the ground and is not dangerous to them. It’s only when the birds get into a part of the power infrastructure where a circuit can be completed that they end up crispy.