If you’ve ever chimney swifts in flight, you know these birds are spectacularly fast and graceful fliers. They have to be because they forage on the wing, capturing enough tiny biting insects each day to equal one third of their body weight! Their feet are not designed for perching the way other birds perch. Instead, they’re more like grappling hooks, enabling them to grip vertical surfaces like the insides of large hollowed out old trees, tree cavities, or caves, which is where they nest and roost. They also have special bristles on the tips of their wing and tail feathers to prop them up when clinging to a vertical surface.
Effects of habitat loss
Chimney swifts range throughout the eastern half of the United States and southern Canada. When early settlers cleared the land for farming, the hollowed out old trees these birds needed for nesting and roosting were lost. The chimney swift adapted to using the chimneys of the homes being built, which are similar in structure and their rough interior. That’s how this bird—sometimes called a swift bird—came to be called a chimney swift.
In rural areas, they may still find the natural nesting and roosting sites they once used. In urban and suburban areas, along with using chimneys, they also use air vents, old wells, abandoned cisterns, outhouses, boathouses, garages, silos, barns, lighthouses, and firewood sheds. Unfortunately, even chimneys are now becoming scarce—at least ones that are useful and accessible for chimney swifts—as new homes are more often being built without chimneys, built with chimneys that have narrow flues or metal liners (more on that hazard later), or have capped chimneys.
Timing of chimney swift migration
If you’re ever near a large chimney, an abandoned cistern, or a silo at dusk near the end of the summer or in autumn, you may see a massive flock of chimney swifts—as many as 10,000 birds—circling overhead and quickly descending into the structure to roost for the night. Sometime around November 1st, a migrating chimney swift must migrate to South America, where she or he will spend the winter. When these birds return in early spring, they’ll have made a round trip of about 6,000 miles. A migrating chimney swift leaves a roosting site at first light in a small group, not with the whole flock. Before proceeding, though, they reassemble, as it’s safer when passing through unfamiliar territory. Along the way, they’ll forage over open terrain, forests, and ponds, and roost together each night.
Behavior of chimney swifts
As you might guess from the fact that large flocks of chimney swifts are willing to share a single structure to roost, the chimney swift is a highly social and communicative species. Roosting together in large numbers can raise the temperature inside a chimney 70 degrees above the outside air temperature, increasing the birds’ ability to survive dangerously cold weather. When they return to North America in spring for the nesting season, though, each chimney swift pair wants a chimney of their own. While the pair may allow unmated individuals in their chimney, as those birds will help with feeding their young, they will not allow other mated pairs to nest there.
Chimney swift family life
Chimney swifts engage in elaborate aerial courtship displays, and pairs go on to have a monogamous relationship for the season. Whether built in a natural or human-made site, the chimney swift’s nest is an efficient and sturdy little structure. It is a small half-saucer shape, about 4” wide, 2-3” from front to back, and 1” deep. Comprised of small twigs woven together, the nest is attached to the wall of the tree, chimney, or other nest site using saliva from a gland under the bird’s tongue. Like many birds, chimney swifts return to the same nest each year, if possible. To make sure the birds are safe, it is important to hire a chimney sweep to clean out your chimney and remove any old nests in mid-March before the swifts return and begin to nest again. Why? Unfortunately, an old nest in a chimney is unlikely strong enough to remain attached to the wall, so reusing it could endanger the next family of nestlings. If you think a swift family may be taking up residence, just make sure to close the damper to minimize disturbance and to prevent an adult or chick from accidently entering your home.
Chimney swift young outgrow their nest within two weeks, often before their eyes have even opened. They must then cling to the wall, awaiting frequent feedings from their parents until they are mature enough to fly. If they are in your chimney, as they become larger you may begin to hear their voices (very loud voices!) when they beg for food. The good news is that by the time you hear the young, they’re usually less than 10 days away from being able to leave the chimney to feed themselves. But if the sound is more than you can bear, stuffing insulation or even old bedding in the fireplace under a closed damper reportedly helps muffle the chatter.
Chicks appear to have a voracious appetite and become hungry faster than the parents can supply them with insects. Here’s where those unmated helper birds we mentioned come in handy! While inside the chimney, the young birds must exercise their wings—fluttering up the chimney, grasping on the wall, dropping down, and fluttering up again—to strengthen their flight muscles and develop coordination. Once they are strong enough to fly, their parents will lead them up and out of the chimney. They’ll fly above other chimneys, with the adults chattering to announce their family to other chimney swifts. They’ll also demonstrate how to catch insects while on the wing, because that’s how the young swifts will now need to feed themselves.
Federal protection of chimney swifts
Chimney swifts eat a wide array of insects, but they’re especially fond of insects humans love to hate, such as mosquitoes, biting flies, gnats, and termites. For this, we should remember to give them both our thanks and the patience they may need if we discover a nest of them chattering in our chimney. As a migratory bird, the chimney swift is protected by the federal Migratory Bird Treaty Act. This means that adults, their young, their eggs, and their nests cannot be tampered with in any way without first obtaining a legal permit to do so.
Caring for your chimney
When hiring a chimney sweep to clean your chimney, always consult the National Chimney Sweep Guild, so you will find a licensed provider who knows the proper timing and techniques for managing your chimney without harming the protected chimney swifts. You can also follow the spring sightings posted online at Chimney Swift Conservation Association. Naturally, you’ll need to delay cleaning until young have left the nest (typically not until the first of November), but ideally, you should consider waiting until after you’re finished using the chimney for the winter to have it cleaned. This is because the built up creosote residue from fires should be removed. If creosote is left on the interior walls of the chimney and the swifts build their nest on it, the nest will be unstable and likely fall with the young inside. Chimneys with metal linings must be capped, as the slippery surface makes it impossible for a swift or any other creature to get out. Chimneys with rough linings offer desperately needed nesting and roosting sites for chimney swifts.
It’s important to note that there is a downside to leaving a chimney uncapped. A raccoon may decide to take up residence once the swifts have migrated, or a curious squirrel may fall down the chimney with no way to escape. So if you want to encourage chimney swifts to live on your property without the chance of other wildlife later joining, you may want to consider constructing a chimney swift tower.
Just remember, if chimney swifts are living in your chimney and you find yourself ready for them to move on, their presence is short-lived and they will leave soon enough. Further, they’re only using your space because their natural habitat is no longer available. Although they don’t pay rent, you will benefit from their presence. Due to their hefty appetite, a chimney swift family will consume about 12,000 biting insects each day! We’d say that’s a pretty profitable return.