This past autumn, people all across the U.S. southwest were finding an astounding number of dead birds littered along roads, on golf courses, and in their own driveways. Some estimated that hundreds of thousands of the creatures perished. Months later, new findings are shedding a little more light on why the spooky phenomenon may have taken place.
Lab results on bird necropsies from the U.S. Geological Survey’s National Wildlife Health Center, released earlier this month, suggest that starvation was a cause of the mass die-off seen in August and September. 80% of the carcasses the researchers analyzed showed signs of starvation, including emaciation, severely shrunken muscles, blood leakage in intestinal tracts, and kidney failure.
Members of the public reported nearly 10,000 dead birds, including finches, flycatchers, swallows, warblers, and bluebirds, to the USGS in August and September, and they sent some 170 carcasses to the agency. The researchers analyzed 40, of which 32 showed these signs of starvation. The remaining ones weren’t in good enough condition to conduct post-mortem tests.
Malnourishment was the only major commonality the researchers found from their necropsies. The USGS scientists also tested the bird bodies for signs of parasites, bacterial or viral diseases, or pesticide poisoning, but found none of those were among the birds’ causes of deaths. At the time of the die-off, some scholars speculated that smoke from the U.S. West’s record-breaking 2020 wildfire season may have been a factor. But the analysis also found no evidence of smoke poisoning in the birds.
Despite this, Jon Hayes, the executive director of the Audubon Society’s southwest branch, still believes the fires may have played a role. “The birds could have been altering their migration path to avoid smoke plumes, thereby increasing the energy demand of their migration and causing exhaustion,” he told Audubon Magazine. “The evidence they’ve shown regarding poor body condition could still fit that scenario, and so I think there’s still questions like the role of fire in particular.”
Whatever the exact conditions that led to the birds’ starvation, it seems climate-related changes were a major factor. The report does not determine exactly what led to the birds’ starvation, but the researchers say a severe drought in the region over the summer is a probable cause. Amid dry conditions, plants produce fewer seeds, and bugs aren’t able to reproduce as much, all of which spells disaster for avian diets.
After the drought came a massive sweep of cold weather, which the researchers think may have further destabilized the birds’ condition. Around Labor Day in early September, the Southwest saw temperatures fall below freezing, which may have made birds’ preferred food choices even scarcer.
The unexpected cold front and winds may have also disoriented the birds, causing them to fly into objects and buildings. “Some were struck by vehicles and many landed on the ground where cold temperatures, ice, snow and predators killed them,” USGS said in a press statement.
The findings are a warning sign of difficult times ahead for birds. As the climate crisis worsens, studies show the American West and South will see far more frequent and severe dry spells. Seemingly random spurts of cold weather will also become more common.
A 2019 report found that North America has already lost 30% of its birds since 1970, and changes in climate bear a large part of the blame. Another report last year found that 389 bird species—including some impacted by the 2020 southwestern die off, like warblers—are facing potential extinction due to changes in temperatures and precipitation patterns.
The die-off makes it clear that the world must get its act together on the climate crisis by rapidly drawing down our greenhouse gas emissions. If we don’t, all species, including birds, will suffer. Since birds regulate bug populations and pollinate plants, the effects of their decline will be felt throughout entire ecosystems, including by humans. It’s in our best interest to help them out.