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In many towns east of the Rocky Mountains, the chattering calls of Chimney Swifts are as much a part of summer’s soundtrack as the cha-cha of sprinklers or ice cream truck jingles. Swifts cut a unique profile often described as resembling a cigar with wings, but that’s far from the only thing that sets them apart.

From their unusual anatomy to their nesting behavior, Chimney Swifts are among the strangest of our common avian species. The more you learn about these fascinating birds, the more likely you are to become a hardcore, um, Swiftie. 

1. Chimney Swifts are among our most urban birds. As their name suggests, they nest in chimneys or abandoned buildings, and you’re most likely to find them in cities and towns with plenty of such places to take shelter. It’s a pattern that began after European settlers built chimneys and other attractive nest sites across the landscape—including wells, barns, silos, and outhouses—producing a population boom for swifts.

2. But it wasn’t always so. Before settlers cut down old-growth forests, swifts nested mainly in hollow trees. In his Ornithological Biography, written in the 1830s, John James Լ����Ƶ vividly described a massive hollowed-out sycamore near Louisville, Kentucky, where, some two decades earlier, he found what he estimated were 9,000 swifts roosting. Լ����Ƶ was there one morning when the birds began to exit the roost, and he “listened in amazement to the noise within, which I could compare to nothing else than the sound of a large wheel revolving under a powerful stream.”

3. These days Chimney Swifts rely heavily on humans to provide nesting and roosting sites, but their ancient connection with trees lives on. In recent years thousands of swifts during fall migration in the Davie Poplar, a nearly 400-year-old, partially hollow tree on the campus of the University of North Carolina at Chapel Hill. Swifts also reportedly make use of hollow, old-growth trees in the Amazon rainforest, along with chimneys and other human-built structures.

4. Beyond that, not much is known about the species in its nonbreeding territory, which includes parts of Brazil, Chile, Ecuador, and Peru. Scientists say there’s a real need for more research to better understand this portion of Chimney Swifts’ life cycles, especially since populations have plunged by more than 50 percent over the past 50 years, according to the 2025 State of the Birds report.

5. If Chimney Swifts live in your area, you should be able to find them—just look up. These aerial specialists spend nearly all their waking hours on the wing, where they might catch more than 1,000 flies, beetles, and other insects in a single day. They also drink water and bathe while in flight by swooping down to a water body’s surface. Because of swifts’ brisk, fluttering flight patterns, people often confuse them with bats.

6. Occasionally Chimney Swifts even copulate on the wing, scientists believe, though they more typically mate at the nest site. During courtship, pairs perform a display flight—a bonding behavior that continues into autumn—in which they snap their wings upward to form a V shape. Another courtship behavior involves small groups of swifts chasing one another, during which the species reaches some of its highest flight speeds, which can exceed 60 miles per hour.

7. When they’re not in flight, Chimney Swifts are typically hanging out, quite literally. Their tiny feet were not built for perching—swifts are not known to land, walk, or hop on horizontal surfaces—and instead have four grappling-hook-like claws that help them cling to vertical surfaces. Like woodpeckers, they also use their stiff tail feathers to prop them while upright.

8. Chimney Swifts have a special tool for building nests: their spit. When the birds arrive at their breeding grounds, typically in March or April, they form pairs and find a chimney or other suitable site to raise their young. They piece together a nest from twigs, holding it together and affixing it to the wall with their glue-like saliva, produced by glands under their tongues that get larger during breeding season. Females lay four or five pure-white eggs, which, with luck, hatch about 20 days later.

9. During migration, vigilant birders can witness an amazing spectacle. At dusk, thousands of swifts form an avian vortex as they swirl downward and dive headfirst into a chimney to roost. Once inside, they quickly flip to face upward and cling to a wall. The same thing happens on a smaller scale during nesting season, which might give the impression that the birds have formed a breeding colony. In fact, typically only a single pair will nest in any given chimney, but they are often joined by dozens of unpaired swifts. When the mercury drops, swifts find warmth in numbers. Their body heat has been known to keep a chimney up to 70 degrees Fahrenheit warmer than the temperature outside.

10. The close connection between humans and Chimney Swifts offers opportunities for people to get involved in protecting the birds. Chimney structures aren’t as common as they once were, and many existing chimneys have been capped, blocking swifts from entry. But Լ����Ƶ chapters and other groups around the birds’ range are working to keep chimneys available for birds and to that serve as good substitutes. (Find some useful tips .) Others host Swift Night Out events, inviting the public to count the birds as they swirl into chimneys and to learn about what they can do to protect these fascinating aerial acrobats.