When dead birds fall from the sky, you know something is wrong. But finding out exactly what killed them isn't as easy.
Scientists had plenty of theories when migratory sparrows, flycatchers, blackbirds, swallows, warblers and other birds in the southwestern United States turned up dead or dying in August and September of 2020. Some suggested it could have been smoke from wildfires. Others said it could have been a cold snap. Some experts thought it was lack of food, as evidenced by the birds' emaciated, dehydrated bodies.
