Mother Swift with young
Chimney Swift at rest Chimney Swift in flight

The Chimney Swift is a member of the swift family which also includes the Black Swift and the White-throated Swift (the common swift west of the Rockies). Chimney Swifts range throughout eastern North America from North Dakota to Maine and south to the Gulf Coast. They winter in Peru. Their closest relative is the hummingbird.
The Chimney Swift is a small bird, roughly 5" long and dark-gray in color. As with all swifts, it has a short bristle-tipped tail and slender, curved-back wings. In flight the swift calls with a twittering of rapid, repeated chips. The Chimney Swift can be distinguished from swallows and martins by its lack of forked tail and its narrow, long wings on a relatively small body. The swift is often described as a "flying cigar". Swifts gather in communal roosts in air shafts or large chimneys, often whirling in a huge circle as they funnel down for the night.
Nesting Habits:
Chimney Swifts begin to arrive in March. A few still nest in large hollow trees; however, most nest in chimneys. Both sexes help in nest building. They hover by trees and break off twigs and are then fastened together with saliva to form a semicircular basket and attached to the chimney wall. By mid-June 3 to 6 pure white eggs are laid. Incubation takes 18 days and then the young usually stay in the nest for 24 days. At first they exercise their wings while staying in the chimney by bracing their tails against the walls and flapping their wings. Both the father and mother help with incubating and raising the young. Sometimes other adult swifts will also help with feeding duties. The young are ready to leave the nest usually in late July to early August. Swifts flock together after the nesting period. They begin to leave in the fall with most gone by late October.
The Chimney Swift and Man:
Chimney Swifts are highly beneficial birds from man's point of view. They are voracious eaters of flying insects including mosquitoes, flies, ants and termites. Unlike martins, they don't mind if a yard has tall trees. Their only requirement to nest is a chimney (non-ceramic) or chimney-like structure. If you would like to have Chimney Swifts nest in your chimney, remove any grate that may be on the top during the nesting season (March - October). The only precaution you must take is to make sure the chimney flue stays closed. When there are young in the chimney, you may hear some fluttering from time to time which sounds very close to the flue. This is caused by the young exercising their wings and is no reason to panic. Swifts leave very little debris in the chimney from their nesting activities and are very clean birds.