There are several species of swifts in the United States, but the chimney swift (Chaetura pelagica) is the most common and widely distributed. In the summer months these sleek, elegant little birds range throughout the Midwest and Eastern U.S., and north into southern Canada.

Before Europeans arrived in North America, chimney swifts nested in the old giant hollow trees of the forest. When land was cleared for agriculture and development, these trees were lost. This change might have had a devastating impact on swifts except for one thing: Houses were then built with stone and mortared brick chimneys, which are almost exact replicas of the nesting trees.

Today, however, many houses are built without chimneys or chimneys that use smaller metal flue pipes rather than clay liners. These metal flues can sometimes be death traps for animals.

Chimney swifts migrate between North America and Peru, making a round-trip journey of 6,000 miles every year to pursue their insect prey, which they take from the air in amazing quantities. Swifts are easily recognizable in flight, with their grey, cigar-shaped bodies, constant wing beats, and distinctive chattering, twittering vocalizations. However, few people ever see them at rest. Chimney swifts are so specialized in their ability to cling to vertical surfaces that they cannot perch or stand on their legs in the way that most birds do. Their unique feet have four grappling, hook-shaped toes with claws that can hold onto a rough surface and partly support them. The stiffened tail feathers, with their exposed spiny tips, bolster them as well. These traits have allowed swifts to make the adjustment from hollow trees to chimneys.

Not only do swifts use chimneys for roosting, but they also build nests in them. Their nests are small and cup-shaped, constructed of twigs and glued to the chimney wall with saliva. During the spring or summer, swifts in a chimney will almost always be a single breeding pair. The brooding and raising of young occurs between June and August. As they prepare to migrate south in the early fall, swifts congregate, sometimes in the hundreds, to use a single chimney as a roost. The nightly return of foraging birds is impressive, as they dart into the chimney at dusk with an uncanny synchronization.

The population of chimney swifts seem to be declining, and it may be due to the relatively recent practice of capping or closing chimneys that were once used for nesting. There is good news for chimney swifts, however. The North American Chimney Swift Nest Site Research Project (NSRP), administered by the Driftwood Wildlife Association, an independent organization in Austin, Texas, has designed and tested alternate nesting structures for swifts. The most elaborate and successful of these is an extra-large birdhouse—really an artificial chimney, 12 to 20 feet high and 2x2 feet in dimension. You can find plans for building one of these towers at the link below, "Providing and Maintaining Nesting Habitat for Chimney Swifts."