Chapman Swifts are a flock of Vaux's Swift, a small migratory bird, that roost in the chimney at Chapman Elementary School in Portland, Oregon, U.S. It is North America's largest concentration of Vaux's Swift. Every evening from mid-August to mid-October, thousands of Swifts gather in the sky over the school shortly before sunset. An estimated count of 1,700 to 35,000 of the birds at varying times has been reported. Shortly after sunset, over a period of 10 to 30 minutes, they fly into the chimney to roost on the c. 1925 brick chimney's interior walls until they depart at sunrise. The school is on the birds' migratory route to wintering in southern Central America and Venezuela. The birds began roosting here in the early 1980s in response to decreased natural habitat—old growth Douglas-fir and forest snags. Vaux's Swift prefer roosting in a standing hollowed out snag. To provide a haven for the flock, the school did not use the heating system during the weeks of roosting. Students and teachers wore sweaters and jackets, especially toward the end of September when classroom temperatures could be 50 to 60 °F (10 to 16 °C). Around 2003, the Audubon Society of Portland, school fundraisers, and corporate sponsors donated $60,000 to $75,000 for an alternate school heating system which is independent of the brick chimney. The chimney is maintained for the birds. The flock attracts several predators, such as Peregrine Falcon and Cooper's Hawk, as well as hundreds to thousands of human spectators."