An unprecedented number of migratory birds are dropping dead across New Mexico in a mysterious mass die-off that’s concerning scientists. 

The number of bird deaths is estimated to be in the hundreds of thousands, "if not millions," Professor Martha Desmond at New Mexico State University (NMSU) told Las Cruces Sun-News.

She explains that biologists from NMSU examined nearly 300 bird carcasses that were found near Doña Ana County last weekend, but they’ve also seen countless reports, photographs, and videos of the phenomenon across the state, as well as parts of Colorado and Texas. The die-off has affected a wide variety of bird species, although it appears to solely affect migratory birds, namely swallows, flycatchers, and warblers. Native species, such as roadrunner or juniper titmouse, appear to be unaffected.

Along with numerous reports of dead birds, many residents in New Mexico have noticed birds acting strangely, exhibiting unusual behavior such as not eating, flying low, moving slowly, or being so lethargic they are hit by vehicles.

The cause of this tragic mystery is still unclear, but researchers are chasing up a few theories. The prime suspect is the wildfires that are currently ripping through California and other states along the West Coast. It’s thought these unprecedented conditions might have somehow sparked the birds to embark on their fall migration earlier than normal. As they moved inland, their typical sources of food and water were dwindling due to the droughts brought by the past long, hot summer. Some are also speculating the birds might have inhaled smoke and sustained lung damage.

This corner of the US also experienced a local cold front in the first week of September 2020, which might have also scuppered the bird's migration plans. In all likelihood, it's a combination of all the factors above. 

To help dig deeper into this mystery, the Southwest Avian Mortality Project is asking local residents to report any dead birds through their app or the iNaturalist website – more information can be found on the website for Carson in New Mexico. Alternatively, they’re asking residents to collect specimens in plastic bags, store them in the freezer, then contact the researchers. Again more information can be found on the Carson website.