Scientists Report Mass Migratory Bird Deaths in U.S. and Mexico

Some of the dead birds found by biologists from New Mexico State University.

Some of the dead birds found by biologists from New Mexico State University. Allison Salas/New Mexico State University

Scientists and birdwatchers are reporting a mass die-off of migratory birds across the southwestern United States and northern Mexico, several news outlets reported. From flycatchers to swallows to warblers, researchers estimate hundreds of thousands to possibly up to a million birds have died in recent weeks. Scientists say they are unsure of the exact reasons for the deaths.

Avian ecologist Martha Desmond, of New Mexico State University in Las Cruces, called the die-off “unprecedented.”

“It’s enormous, the extent of this,” Desmond told Audubon. “We haven’t counted all the species yet, but there are lots of species involved.”

Online reports show mass deaths in New Mexico, Colorado, Texas, Arizona, and as far north as Nebraska, as well as in four states in Mexico, and include migratory species as varied as owls, hummingbirds, loons, and woodpeckers, many of which were migrating south to wintering grounds.

Many of the dead birds have little fat reserves or muscle mass remaining, and some seem to have literally dropped from the sky mid-flight. Scientists recorded the first group of deaths on August 20 in White Sands Missile Range in New Mexico. Researchers suspect that months of extremely dry conditions, combined with unseasonably cold weather in the Southwest, could have triggered an early start to this year’s migrations before some species were physically ready to make the arduous trip thousands of miles south. But now, as the deaths have continued, researchers say smoke from the ongoing wildfires in California, Oregon, and Washington could also be playing a role.

“It could be a combination of things. It could be something that’s still completely unknown to us,” Allison Salas, a graduate student at New Mexico State University, told The Guardian. “The fact that we’re finding hundreds of these birds dying, just kind of falling out of the sky is extremely alarming … The volume of carcasses that we have found has literally given me chills.”

The dead birds are being analyzed by scientists at the U.S. Fish and Wildlife Service forensics lab in Oregon and the National Wildlife Health Center in Wisconsin. Researchers are urging birdwatchers and volunteers to log sightings of dead birds on the website iNaturalist and contact state Fish and Game agencies or the USFWS.