A group of bird carcasses found by Allison Salas in New Mexico on September 13, 2020.
Allison Salas
  • "Hundreds of thousands" of migratory birds are dropping dead across the American Southwest in what scientists are calling the largest mass die-off in recent history. 
  • Scientists first began investigating the phenomenon in late August after numerous reports of clusters of dead birds found in US states including New Mexico, Arizona, Colorado, and Nebraska.
  • Some witnesses had seen the birds displaying unusual behaviour before their deaths, including becoming lethargic or fearless when humans approached them.
  • Scientists are unsure why this mass die-off is happening, but have addressed several factors including climate change and the ongoing wildfires as possible reasons for the deaths.
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Thousands of migratory birds are "falling out of the sky" across several states in the American Southwest, in what scientists are calling the largest mass die-off in recent history.

Swallows and flycatchers are among the bird species that are dropping dead in US states including New Mexico, Arizona, Colorado, and Nebraska, according to Dr. Martha Desmond, a professor in the biology department at New Mexico State University (NMSU), quoted in the Guardian.

"I collected over a dozen in just a two-mile stretch in front of my house," said Desmond, according to the Guardian. "To see this and to be picking up these carcasses and realizing how widespread this is, is personally devastating. To see this many individuals and species dying is a national tragedy."

Scientists first began investigating the phenomenon in late August after "a large number of dead birds" were reportedly found on the US Army's White Sands Missile Range in New Mexico, according to CNN.

Trish Cutler, a wildlife biologist at the military base, told the Albuquerque television station KOB that fewer than half a dozen dead migratory birds are found dead in a typical week.

"This last week we've had a couple of hundred, so that really got our attention," Cutler said, according to the New York Times.

Since then, residents in New Mexico and other states have reported seeing more clusters of dead birds in locations ranging from hiking trails, golf courses, and suburban driveways.

In one video posted on Twitter, journalist Austin Fisher films dozens of dead birds he discovered while on a tubing trip in New Mexico's Rio Arriba County on September 13.

"I thought to myself, 'Wait, I've never seen this many dead animals in one place in my life," Fisher told the New York Times.

Watch the clip below: 

Desmond said scientists are unsure how many birds are dying but has said the number could easily be in the "hundreds of thousands", according to NBC.

Witnesses had seen the birds displaying unusual behaviour before their deaths, including becoming lethargic or fearless when humans approached them. Other species who usually rest and eat in trees and shrubs were also found hopping on the ground looking for insects, according to Desmond. 

Not all birds seem to be affected. Bird species native to the area including the curve-billed thrashers, great-tailed grackles, and white-winged doves appeared to be in good health.

Climate change and the wildfires could be to blame

Scientists are unsure why this mass die-off is happening. 

Some suggest that the wildfires raging across the American West Coast could be to blame, with smoke plumes potentially altering migration routes or increasing toxins inhaled by birds. 

The Oregon Department of Fish and Wildlife said on Twitter that "not much is known about the impacts of smoke and wildfires on birds."

"Many of them have little to no fat, many are underweight, and there's not a lot of external signs that they have been inhaling a lot of smoke," Jenna McCullough, a doctoral ornithology student from NMSU said, according to the Times. 

Another theory is that the smoke plumes are forcing the birds to fly inland and over the Chihuahuan desert, which offers little food or water. Some carcasses lacked muscle mass and appeared to have nose-dived into the ground because their faces were damaged.

"They're literally just feathers and bones," said Allison Salas, a graduate student at NMSU who has also been collecting carcasses and sending them to forensics laboratory, according to the Times. "Almost as if they have been flying until they just couldn't fly anymore."

Other experts highlighted a cold snap in the Mountains West, or a drought in the Southwest of the region that depleted the insect populations that many migratory birds feed on.

Records that date back to the 1800s show that large avian mortalities during the migration are usually associated with extreme weather events — with the largest event linked to the 1904 snowstorm in Minnesota and Iowa that killed 1.5 million birds, according to the Guardian.

Scientists have said it will take time until they uncover what the reasoning behind the mass die-offs is.

"It could be a combination of things. It could be something that's still completely unknown to us," said Salas.

Scientists continue to study the phenomenon. They are urging people to report any sightings of dead birds on a citizen science website called iNaturalist.

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