Migrating chimney swifts flock into a Pittsburgh chimney en route to South America; October 6, 2015. Recorded from the 5th floor. Over the past few thousand years, these birds have evolved to live in chimneys and other man-made structures, descending from a species of swift that nests in the hollow trunks of dead trees.. They spend almost all of their waking hours on the wing, and sleep in nests adhered to sheer vertical walls with their sticky saliva.
