Tonight, while you're asleep, several hundred million birds will fly over the United States in the dark. Most of them will pass directly over your house, a few thousand feet up. More than 80% of North America's migratory birds travel at night. Warblers, thrushes, orioles, tanagers, sparrows. Birds that weigh as much as a few coins, crossing a continent between sunset and sunrise, navigating by stars and by the earth's magnetic field. Mid-September through early October is the peak. On the biggest night ever recorded, radar picked up 1.25 billion birds aloft over the US at once. And there's one thing standing in their way that you personally control: your lights. Artificial light pulls night-migrating birds off course from as far as three miles away. Once they're drawn in, they circle the lit area, over and over, burning fuel they can't spare, until they either drop from exhaustion or hit glass. It's worst on low, foggy nights, when birds fly closer to the ground and the light bounces off the cloud ceiling. Building collisions kill somewhere between 365 million and nearly a billion birds a year in this country. In Chicago in fall 2023, close to 1,000 birds died against a single convention center in a single day. Two things you can do tonight to help them out: 1. Turn off non-essential outdoor lights between 11pm and 6am. Porch, floods, landscape uplighting, the string lights on the deck. All of it. 2. Close your blinds. Interior light spilling through a window does the same thing as an outdoor fixture, and it's the one people never think of. One more thing worth doing, purely for yourself. BirdCast runs live migration radar and it will tell you how many birds crossed your specific county last night. Not an estimate for the region. Your county. Go look at the number, then go outside and stand in the dark knowing it. If you want to actually see some of it, watch the sky at dusk over the next couple of weeks. Common nighthawks are one of the few migrants that move in the evening, in loose scattered flocks, flying with a stiff-winged flicker and a white bar near each wingtip. Most people who see them assume they're bats. North America has three billion fewer birds than it did in 1970, and long-distance migrants took the worst of it.