Think of them as “flying cigars,” one of several descriptive nicknames for birds first named “American swifts” by early naturalists and later in the nineteenth century renamed chimney swifts. Their short, bluish-black bodies with silver gray throats and squared-off tails flutter bat-like through the air on long, scythe-shaped wings. “Bows and arrows,” another nickname, can best be imagined when they are flying high in the sky, their wings shaped like bows and their bodies like arrows.
Still other nicknames for these flying insect predators are “chimney sweeps” and “chimney swallows.” Like swallows, they rarely alight, but when they do, they cannot perch. They can only cling to vertical rough surfaces even though they have the three toes forward and one toe (hallux) backward of songbirds. But unlike songbirds, chimney swifts can shift their hallux forward to grip the insides of hollow trees in old-growth forests where once they nested and roosted before the arrival of European settlers.
Those settlers quickly cut large trees to build houses with chimneys, and the displaced swifts found new, abundant nesting and roosting sites. Instead of what scientists think were once birds thinly-distributed throughout the eastern forests of North America, chimney swifts became an abundant species that spread as settlers moved into the Great Plains states east of the Rockies from Saskatchewan in Canada south to Texas.
In addition to home chimneys, they have roosted in abandoned large industrial chimneys, stacks, incinerators or air shafts and nested in old wells, abandoned cisterns, outhouses, garages, silos, barns, boathouses, lighthouses, and firewood sheds. Although they probably still nest occasionally in large hollow trees, most notably in abandoned pileated woodpecker nest trees, what were once wilderness birds are now almost solely birds of towns and cities.
I will embed a brief YouTube video showing thousands of chimney swifts flying into an industrial chimney in Gainesville, Florida.
On our mountaintop property in west central Pennsylvania, I rarely see them until the second week in May, yet birders in cities and towns report them as early as mid-April. Widely distributed in every Pennsylvania county, their highest densities occur in Allentown, Erie, Harrisburg, Philadelphia, Wilkes-Barre and especially Pittsburgh’s industrial river corridors, according to the Second Atlas of Breeding Birds in Pennsylvania.
Usually, I first see them in spring in the sky above First Field seining the air for insects. They can scoop up dozens of tiny insects at a time. Their wings beat so fast that many observers once thought they were flapping their wings alternately, which is not aerodynamically possible and was disproved by stroboscopic photography in 1950.
Because they spend the daylight hours airborne and their nights in chimneys, researchers have had a difficult time observing their lives. But one woman, Althea Sherman of National, Iowa, designed and had a chimney swift tower built in her backyard. Beginning in 1918, Sherman, who had been watching and writing about birds for decades, spent her arthritic old age (65 to 83) climbing the tower stairs and watching the birds through special windows that allowed her a view from bottom to top of the 28 foot-high tower as the swifts built their nests and raised their young. She also spent many nights with a lighted lamp watching them at rest and proved that they never feed their young then.
Since Sherman’s research, other ornithologists have pieced together the lives of these amazing birds. Once they return to their nesting sites, they engage in trio-flying, which consists of one female and two males following each other and calling as they fly around buildings and trees and then ascend high in the sky where they fly horizontally.
Another display seen all season, which probably helps them keep their monogamous pair bond, consists of one flying behind the other, when the rear bird suddenly snaps its wings upward to form an acute angle.
They return year after year to the same mate and nesting place as Sherman discovered. Both parents construct the nest by breaking off twigs from branches with their feet as they fly, carrying them back to the nest site, and sticking them in place with glutinous saliva they produce from enlarged salivary glands. At eight to 12 twigs a day, it takes them a week to construct a half-moon nest on the side of the chimney strong enough to hold as many as six white eggs.
Both parents incubate the eggs, and the incubating parent waits until the foraging parent returns before leaving the eggs to forage. After an average of 19 days, the eggs hatch, and again both parents brood their naked young and forage for food.
Paul and Georgean Kyle, authors of Chimney Swifts: America’s Mysterious Birds Above the Fireplace, have been watching and rearing chimney swifts since 1983 and write that hatchlings are so active the parent brooding them “appears to be atop a popcorn popper.” When the nestlings settle down to sleep at night one will utter soft, single notes, a monotonous lullaby“me-me-me,” as it sleeps.
For the first week, parents feed each nestling with a slurry of insect body parts and saliva which they regurgitate into their offspring. Then they start feeding one nestling at a time with a bolus containing dozens of insects. They also allow helpers at the nest to assist them. Usually they are the previous year’s offspring and more often males than females. They will roost with the family at night and may even help incubate the eggs and brood the nestlings.
Many chimney swifts don’t breed every year and while only one breeding pair will occupy a single chimney, they may be joined by roosting unmated birds. Chimney swifts are intensely sociable, feeding together, skimming lakes and rivers for water together, and even flying over each other’s nest chimney and looking inside. The Kyles have seen the brooding parent move aside as if to show off the hatchlings to those stalling over their chimney.
At 19 days of age, the nestlings begin perching on the wall beside their nest and practicing flying. When they are 28 days old, they fly out of the chimney, although they return to roost with their parents and siblings for one to two weeks. As soon as they fledge, they feed themselves the gnats, mosquitoes, flies, winged ants, termites and other airborne insects they find.
In Pennsylvania they most often nest in June. Migrants begin appearing in the commonwealth by mid-August, and in early September form large communal roosts. Alert observers near such roosts can watch in the evening as swifts, sometimes numbering in the thousands, swirl around the entrance of a commercial chimney before suddenly flying down it at dusk.
Although they may remain as late as early October, most start migrating along our ridges in loose flocks in September, stopping each night in another chimney as they head south. Eventually, they fly over the Gulf of Mexico and then overland to reach their wintering grounds in Peru, northern Chile, and northwest Brazil.
According to the 2014 State of the Birds2014 State of the Birds “Common Birds in Steep Decline,” chimney swifts have lost more than half their global population in 40 years. The North American Breeding Bird Survey reports a 65% decline and estimates a population of 7.8 million. In Pennsylvania we’ve noted a 27% decline between the first and second breeding bird atlasing projects, so in 2005 the chimney swift was listed as a species of Maintenance Concern in our Wildlife Action Plan.
Researchers aren’t certain why their numbers are declining. One reason may be the loss of masonry and clay chimneys and the capping of chimneys leading to “habitat loss.”
In 2012 a study found that aerial insectivores have experienced guild-wide population declines throughout North America.
Calvin L. Cink, one of two authors of The Birds of North America chimney swift account, writes that the “total impact of temperature extremes and heavy rains…appear to be important for this species.” Furthermore, in a study he did he proved that high summer temperatures for extended periods can kill entire broods. In summary, he concludes that the decline is likely due to changes in prey abundance, chimney numbers, and weather as well as unknown threats during migration and on the wintering grounds.
To help chimney swifts, the Kyles designed and built a variety of towers to attract chimney swifts and other folks have followed the directions in their book. Most of the towers have attracted the birds as soon as they are constructed.
Here in Pennsylvania, for instance, the Audubon Society of Western Pennsylvania has been building and installing chimney swift towers as part of their Chimney Swift Conservation Program. In addition to constructing them on their Beechwood Farms property, they have partnered with the Allegheny County Parks Foundation to build them in all nine county parks. As of July 2016, they’ve constructed 22 towers in North Park and are starting to build them in South Park.
Cink and his co-author Charles T. Collins also urge that “nest and roost trees (large diameter, hollow trees) should be identified and preserved in old-growth stands of forest,” so that the birds can use their precolonial nesting places.
I enjoy watching them on humid August days and evenings as they fly over First Field, scooping up insects in company with barn swallows and preparing for their long migration south to another continent, and I hope that we can provide enough safe places for them to nest so that the sight of thousands flying down to roost in a large chimney will not become a memory of the past.
I’ll close with a fascinating video of three young chimney swifts being fed by a parent bird.