Researchers in New Mexico estimate that hundreds of thousands of migratory birds have died recently across the state, with climate change and the massive fires in the Western U.S. among the possible causes.

Martha Desmond, a professor at New Mexico State University’s Department of Fish, Wildlife and Conservation Ecology, told CNN that researchers discovered a large number of dead birds at the U.S. Army White Sands Missile Range and White Sands National Monument late last month. 

Additional groups of dead birds were also found in Doña Ana County, Jemez Pueblo, Roswell and Socorro. 

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"It's just terrible," Desmond told CNN. "The number is in the six figures. Just by looking at the scope of what we're seeing, we know this is a very large event, hundreds of thousands and maybe even millions of dead birds, and we're looking at the higher end of that."

Species represented among the dead include warblers, bluebirds, sparrows, blackbirds and more. Groups of the dead birds are also being found in Colorado and Texas, as well as in Mexico. 

Trish Cutler, a wildlife biologist at White Sands Missile Range, said “resident birds” in the area have not been impacted, the Las Cruses Sun News reported.

Researchers identifying and cataloging the dying animals have said that the birds were acting strangely for their species before their deaths, such as ones usually seen in trees searching for food on the ground. 

Cutler told local station KOB 4 that “on the missile range we might in a week find, get a report of less than half a dozen birds.”

“This last week we've had a couple hundred, so that really got our attention.”

Desmond said that some of the birds that have died recently were lethargic and hit by cars.

She also said that the wildfires burning across the West Coast could explain the mysterious deaths, causing birds to migrate early.  

"Birds who migrated before they were ready because of the weather might have not had enough fat to survive," Desmond said. "Some birds might have not even had the reserves to start migrating so they died in place."

Some of the birds also may have inhaled smoke from the fires and damaged their lungs. 

Desmond told CNN that long-term climate change is also “playing a role” in the bird deaths.

"We lost 3 billion birds in the U.S. since 1970 and we've also seen a tremendous decline in insects, so an event like this is terrifying to these populations and it's devastating to see."

The birds collected by researchers will be sent to the U.S. Fish and Wildlife Service Forensics Laboratory in Ashland, Ore., for examination.