750,000 birds flew over the Seattle area while we slept

By the numbers: BirdCast estimates 751,700 birds crossed King County Thursday, with traffic peaking around 12:50am when about 279,000 birds were simultaneously in flight.

• Across Washington, more than 3.6 million birds migrated overnight, traveling southeast at an average 25 mph, 3,700 feet above the ground.
• BirdCast says migration generally begins 30–45 minutes after sunset, with the greatest number of birds aloft two to three hours later.

Stunning stat: On Sept. 1, just 1,700 birds were estimated to have crossed the county. Two days later, that number jumped to almost 420,000.

Who's flying: Nighttime migrants moving through our region typically include western sandpipers, black-throated gray warblers, western wood-pewees and willow flycatchers.

How it works: BirdCast uses weather radar — the same system that tracks rain and storms — to detect and estimate birds migrating through the night.

The bottom line: The calendar may still say summer, but the birds are telling us it's fall.