A purple martin (Progne subis) in flight at Wakodahatchee Wetlands in Delray Beach, Florida, on April 29, 2026. The species migrates annually from South America to North America to breed, traveling thousands of miles each spring. Credit: Ronen Tivony / NurPhoto via Getty Images Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. Tonight, there will be more birds in the sky than there are people in the United States. According to Cornell Lab’s BirdCast , an estimated 373 million winged migrators will continue their journey north during the early evening hours of May 4th. Most of the activity will be visible in the South and along the East Coast, but wildlife experts are politely reminding everyone hoping to catch a glimpse of the traveling birds to make sure you’re not blinding them from below. Birds migrate for two primary reasons: food and nests.…