The Chimney Swift (Chaetura pelagica) is one of four regularly occurring species of swifts found in North America, and the most common one found east of the Rocky Mountains. Historically these swallow-like birds nested in large hollow trees. But as their contemporary name implies, they are now accustomed to building their nests primarily in chimneys and other similar structures such as towers that are built specifically for their use.
Chimney Swifts are most commonly seen in flight -- usually in groups. When soaring, their long, scythe-shaped wings span about 12.5 inches (31.75 cm), and support a proportionally short body with a squared-off tail. The flickering, bat-like flight when flapping is due to short, relatively massive wing bones. A sharp “chippering” or “ticking” call accompanies Chimney Swifts’ flight.
At rest, their long wings cross by an inch or more over the tail feathers, which are tipped by pointed bristles. Average adult Chimney Swifts are about 5 inches long (122 cm), and weigh 0.8 ounces (22.8 gm). They are sooty-gray to bluish-black with the throat a lighter silvery-gray in color. Both sexes are identical in appearance. The strong claws and stiff tail bristles of Chimney Swifts allow them to cling to rough vertical surfaces. Swifts are unable to perch or stand upright like songbirds.
The keen eyesight and impressive flight abilities of Chimney Swifts make them proficient predators of small flying insects – also known as “aerial planton”. Their diet includes mosquitoes, midges, flies, flying ants and termites. A single Chimney Swift will eat more than 1000 mosquito-sized insects each day.
Chimney Swifts winter in northwestern South America, generally in and around Peru. They arrive in the southern United States in March and nesting begins as early as mid April.
Chimney Swifts will usually have only one brood per year. However, if conditions are favorable at a nest site a pair may raise a second brood. If the first nesting attempt is unsuccessful, Chimney Swifts will usually try again.
The female normally lays four to five (rarely one to seven) white eggs in a nest of twigs that are harvested from the tips of tree branches with the feet, transferred to the bill, and attached to a vertical surface with glue-like saliva. Both sexes are involved in nest construction. Because the nest is unlined, alternating adults must constantly incubate the eggs. Trading off is accompanied by a vocal exchange between the parents.
After 18 to 21 days, the eggs begin to hatch. Baby Chimney Swifts are fed by both parents. While one parent broods the young, the mate goes out to forage. When it returns, it feeds the babies and replaces its mate on the nest. The babies are seldom left unattended during their first week of life.
The hatchlings are pink, naked and completely helpless when they emerge from the eggs. However, they have sharp claws that enable them to cling to textured surfaces, and they chatter softly when stimulated. Within a few days, black pinfeathers begin to appear. The young are able to climb, and they exhibit preening behavior even before their feathers emerge.
By the time they are ten days of age, the feathers of young Chimney Swifts begin to unfurl. Young Chimney Swifts are capable of a variety of vocalizations. From this age until they fledge they will erupt into a raucous explosion of chattering whenever adults enter the nest site. When disturbed or frightened they will make a loud, repetitive rasping call that sounds much like mechanical wind-up toys. At night one or more young birds may "sing". The soft rhythmic "peeping" is in dramatic contrast to their more well known vocalizations.
By fifteen to seventeen days of age, their eyes will begin to open. The eyes are at first a milky-blue in color, but they turn brown by day twenty-one. Birds, which have been stressed by excessive heat, emaciation or are separated from their parents, may have their eyes open at a much earlier age.
Shortly after their eyes open, most of the flight and body feathers will be unfurled. However, the feathers around the face and head will stay in sheath for several days – giving the birds a “frosty-faced” appearance.
When Chimney Swifts are 21 days old, they will begin to venture off the nest for short periods, often roosting on the wall directly under the nest. At this age they will begin to "practice flap". Clinging tightly to the nest or chimney wall, they will rear back and flap their wings furiously until they are panting and out of breath. For the next five to seven days they will become more active, flying up and down the inside of the chimney like miniature helicopters. Twenty-eight to thirty days after hatching, young Chimney Swifts will leave the safety of the chimney for their first flight.
Once an entire brood has fledged, they will fly with their parents in slow, noisy parades around the area of the nest site. Because the adults begin to molt soon after their arrival in North America, they are easily distinguished from the young in flight. The adults will have a ragged appearance with several missing flight feathers forming "windows" in their wings. In contrast, the hatchling-year swifts will have sleek, full wings.
The young will return frequently to the roost during the first few days, but may soon begin to visit other roosts in the area. By the time young swifts fledge, they are capable of feeding themselves, though they may still beg occasionally if they are in the roost when an adult enters.
Chimney Swifts are solitary nesters (one nesting pair to a site). The adults will defend the nest site from would-be interlopers by audibly snapping their wings together over their backs while jumping horizontally from the wall. They will then drop to a lower spot on the same wall. These spirited displays are often accompanied by loud "chippering" and wing fluttering which can be easily heard from outside any nest site. Despite their defensive behavior, the nesting pair will tolerate and often welcome a few additional birds at the nest. These “helpers” are most commonly second-year birds. They will actually take part in feeding and caring for the babies. Because of this cooperative behavior, it is conceivable that the death of one of the parents after the eggs hatch may not mean the death of the brood. As young swifts approach fledging age, the parents become more tolerant of visiting birds, and a communal roost may begin to build.
At the end of the breeding season, territorial behavior is completely replaced by their communal instinct that peaks prior to fall migration.
Chimney Swifts will congregate in flocks of hundreds and even thousands at suitable roost sites. These sites are easily identified in the late evening as the swifts gather and fly in a huge circular cloud around the mouth of a chimney-like structure. Slowly at first, a few birds will disappear into the darkness of the roost. Then, as if by pre-rearrangement, the entire flock will stream in within just a few minutes. Their emergence at first light is sporadic and even haphazard by comparison.
Although Chimney Swifts can withstand a few early cool snaps, they will usually ride south on the first major cold front that blows through in the fall. By the 1st of November, Chimney Swift sightings in the United States are very rare.
Chimney Swifts are one of our many declining avian species. Breeding bird surveys have indicated that their numbers are down by more than 44% since the mid 1960s in the continental United States. On the northern fringes of their range in Canada their decline is a dramatic 95%. Loss of their natural habitat of large hollow trees, capping and demolition of masonry chimneys and airshafts to which they have adapted and the use of pre-fabricated metal chimneys in new construction are all playing a part in the decline of this unique and beneficial species.
For more information about Chimney Swifts and the ongoing conservation efforts on their behalf, please visit the Driftwood Wildlife Association’s website.
Copyright 2005 Paul D. Kyle and Georgean Z. Kyle