Scientists don’t know why hundreds of thousands of birds are dying off in the southwest.
People started observing large numbers of dead or lethargic birds at the White Sands Missile Range in New Mexico on Aug. 20, says Martha Desmond, professor at New Mexico State University's Department of Fish, Wildlife and Conservation Ecology. Ornithologists like Desmond thought this was an isolated incident until around Sept. 9, when a large weather event moved across the western U.S. as birds migrated south for the winter.
“A lot of birds up north were probably caught off guard,” she says. “It's unusual, but it does happen where we do see die-offs of birds in the spring or in the fall with weather events.”
Weather events such as hail or snow storms can kill thousands or occasionally a larger number of birds, she says. While the weather contributed to the die-offs, Desmond says it’s “troubling” that ornithologists were seeing dead birds before these events happened.
Fires burning in the West could have forced birds to change their migratory routes, leave early or inhale smoke and damage their lungs, she says, which may cause odd behavior and large numbers of deaths.
Researchers have seen up to a dozen swallows die in groups as they roost together in nests — one of many odd bird behaviors being observed, she says. Near northern New Mexico’s sulfur hot springs, birds are dying in small groups in caverns or burrows in the ground.
“We're seeing birds in lethargic conditions where they're just sitting on the ground and you can walk up to them,” she says. “We're seeing birds that normally are in shrubs and trees feeding on insects are running around on the ground chasing insects down.”
Experts don’t know if this phenomenon is related to climate change, Desmond says. But it’s been a dry year in New Mexico, she says, which causes a problem for insectivorous birds who reroute their migration to the state.
“We're seeing some birds that we normally don't see,” she says. “If they're landing here and then there isn't enough food for them to feed on — certainly enough insects — that could cause some of them to starve to death. And that is a drought-related phenomenon.”
To assess the magnitude of the problem, researchers set up the Southwest Avian Mortality Project on the app iNaturalist so people can share photos and observations.
Nearly 3 billion birds have died since 1970 in North America. “Drastic declines” in insect populations on the continent could have a huge effect on the feathered creatures, she says.
“An event like this — where so many birds have died in populations that are already stressed and species that are already declining — could definitely have an enormous impact,” she says.
This segment aired on September 15, 2020.