More than 16 million birds have flown over Arlington under the cover of darkness so far this fall.
That’s about 19% above the historical average for this point in the season, according to the Arlington County migration dashboard from BirdCast. BirdCast is a Cornell Lab of Ornithology project that uses weather radar to estimate how many birds are in the air each night.
The busiest night of the season so far was over the weekend. An estimated 2,347,700 birds crossed the county between dusk Saturday (Oct. 17) and dawn Sunday. The flight peaked around 1:15 a.m. Sunday, when about 43,000 birds were in the air at once. They were heading southwest at about 40 mph, roughly 2,700 feet up.
The night before, BirdCast recorded its fourth “billion bird night”. Around 10:45 p.m. Friday, more than 1.03 billion birds were in flight over the contiguous U.S. That flight was concentrated over Texas and the central and lower Mississippi River valley, behind a strong cold front, BirdCast said.
The record is about 1.25 billion birds in flight on the night of Oct. 8, 2025, according to AccuWeather. The other billion-bird nights in BirdCast’s records were Oct. 6, 2023, and Sept. 25, 2025.
Migration over Arlington has kept going this week. An estimated 1,015,200 birds crossed the county Tuesday night. Last night (Wednesday), the total was about 317,500. Traffic peaked around midnight, when about 8,400 birds were in flight, heading south-southwest at 31 mph and about 2,300 feet up.
The dashboard uses eBird observations to list the night-migrating species most likely to be arriving in or leaving the area this time of year. The top of the list includes ruby-crowned kinglets, yellow-rumped warblers, dark-eyed juncos, hermit thrushes, common yellowthroats and yellow-bellied sapsuckers.
BirdCast tracks fall migration from Aug. 1 through Nov. 15. Historically, about 18.4 million birds cross the county over the full season.
Most of those birds travel at night, and bright lights from buildings can disorient them. That can lead to collisions with glass or to birds exhausting themselves circling lit structures, according to the Northern Virginia Bird Alliance. The group estimates that 160 million birds migrate south through Northern Virginia each fall.
The alliance’s Bird Safe NOVA campaign asks building managers and residents to turn off or dim nonessential lights from 11 p.m. to 6 a.m. through Nov. 15.
Bird collisions have also come up in Arlington’s development reviews. In 2023, then-County Board Vice-Chair Libby Garvey asked whether the county would strengthen standards for bird-friendly glass. Her question came after about 1,000 migrating birds died hitting a single Chicago building. Bird-friendly glass was not required at the time.
Another bird mass casualty event was reported in Chicago this past weekend.
Planning commissioners have since pressed developers on the issue, including on several projects last year and an affordable housing proposal off Langston Blvd earlier this year.
Flickr pool photo by Jim Harvard
