This large chimney used to be the exhaust of the boiler at Chapman Elementary School in Portland, OR. But, now it's most famous as one of the largest and most visible roosts of migrating Vaux's Swifts. Each evening in the late summer, tens of thousands of the small birds funnel into this chimney. How do they fit? I have no idea. The event has become quite a spectacle, with hundreds of eager birdwatchers arriving each evening to witness the ritual.