As spring turns into summer, afternoons and evenings at my home have presented daily shows from a small flock of resident chimney swifts. These graceful and aerodynamic birds are designed for a life lived almost exclusively on the wing. In fact, chimney swifts are incapable of perching in the manner of most birds. They can only cling to vertical surfaces, such as rocky cliff faces or the interiors of chimneys.

As they fly overhead, these swifts produce a high-pitched twittering. It’s not as musical as the songs of some birds, but neither is the sound unpleasant. In fact, the twittering of chimney swifts is a sound that I’ve grown to associate with pleasant summer evenings. Listening to these birds as they swoop in the sky overhead is a great way to relax.

Chimney swifts are often most prevalent over the rooftops of cities, but swifts also spend the summer months in more rural areas. Flocks returning to summer roosting sites at dusk are an impressive sight. Hundreds of these birds can swoop in ever tightening circles around a large chimney, disappearing inside the chimney like feathered smoke.

Former names for the chimney swift have included chimney sweep, American swift and chimney bat. These birds, however, do nothing to clean the inside of chimneys, and bats are, of course, mammals. Swifts are not difficult to recognize, and their overall shape has often been described as “cigars with wings.” They are designed for flight and feed almost exclusively on winged insects. They even bathe on the wing, flying low over rivers and other bodies of water and skimming the surface in order to dampen their breast feathers.

In the United States, the chimney swift is the only member of its family found in the eastern half of the country. On the other side of the continent, the white-throated swift, Vaux’s swift and black swift replace the chimney swift in the western United States and southern British Columbia in Canada.

Worldwide, there are about 75 swift species. The family also consists of birds known as swiftlets, needletails and spinetails, but they’re all just variations on the the basic swift model. Some of the world’s other species include band-rumped swift, pale-rumped swift, white-throated swift, white-tipped swift, mottled swift, plume-toed swiftlet, drab swiftlet, silver-rumped spinetail and brown-backed needletail.

The largest member of the swift family is the purple needletail, a species native to Asia. This bird is almost ten inches long and can weigh nearly seven and a half grams. Another species, the cliff swift, makes a nest that is prized in Asian cuisine as an ingredient for “Bird’s Nest Soup.” The governments of various Asian nations regulate the harvesting of nests quite strictly to ensure that the human demand for the soup doesn’t deplete the overall swift population. It’s a lucrative enterprise, however, and some experts worry that poaching and unethical harvesting methods, such as taking the nests before young birds are capable of flight and survival, could endanger the swifts.

Fortunately, nests of chimney swifts in the New World have never become coveted for culinary purposes. According to the Tennessee Wildlife Resources Agency website, chimney swifts once nested and roosted in hollow trees in old-growth forests. When European settlers arrived, they greatly increased the number of potential nesting sites for swifts by putting chimneys on their buildings. The responsive swifts quickly took advantage of these new nesting and roosting sites. They build their nests, whether in chimneys or hollow trees, of twigs cemented together with their own saliva.

While chimney swifts are spread across much of the eastern United States during the nesting season, their winter home remained unknown for many years. In 1943, Peruvian natives recovered bands that had been attached to the legs of 13 swifts, helping to finally solve the mystery of where the birds spent the winter months. According to an article on the TWRA website, eight of the 13 bands came from birds that had been banded in the Volunteer State.

Of course, swifts are not the only birds in the summer skies. Taking a moment to gaze upward can reward you with views of soaring raptors, swooping swallows and foraging common nighthawks.