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Ornithological Studies Presentation
Roosting Swifts in Philadelphia
by Jane Henderson
Video of 2003 Roost (Six second clip in *.avi format - 436 KB. Best viewed with Windows Media Player)
Recently Bird Watcher's Digest (Vol. 20 No. 4 April 1998) published an article written by DVOC member Jane Henderson about Chimney Swifts. This article is available below. The DVOC thanks Bird Watcher's Digest for their permission to share this information.
Chimney Swifts by Jane Henderson
From late spring until early fall in the Philadelphia area where I live, one of the cheeriest sounds we hear is the chitter of chimney swifts as they swoop overhead in search of insects. Even downtown, over the noise and the bustle of traffic and crowds of people, the chimney swifts' call can easily be distinguished above everything else.
Many people nickname this little bird "the flying cigar." It's not difficult to figure out why. The body of this 5 1/4 inch bird is actually shaped like a short, stubby cigar. In flight, its stiff wings resemble an arched bow or boomerang. Against the sky, the bird appears to be entirely black, but up close one can see that it is actually a dark brownish-gray.
In September, when we gather on our local hawkwatch, at Militia Hill in Fort Washington State Park, to search the sky for early migrating raptors, the chimney swifts do a pretty good job of looking like falcons from a distance. "In the notch ... I think it's a kestrel ..... oh, no, sorry .... it's just another chimney swift." But that's about as negative as anybody ever gets about these birds.
But it's not until mid-September that birders' talk seriously turns to chimney swifts. It is at that time of year that these birds engage in a truly spectacular pattern of behavior that draws people from miles around to witness what can truly be called a birding phenomenon: their gathering, by the thousands, in swirling masses, just before funneling down a chimney to roost for the night.
Along their southward migration path, these birds have to find suitable places to roost overnight. Prehistorically, they roosted in hollow trees. But in more recent times they have found that barns and chimneys serve their purpose quite nicely. In fact, according to Paul Erlich's Birder's Handbook, with the arrival of the Europeans and the building of vertical structures in the New World, the chimney swifts' numbers substantially increased. They continue to co-exist successfully with humans.
The large, square chimney of the Shawmont School in the Roxborough section of Philadelphia has served as a chimney swift roosting site for many many years. The schoolyard provides an excellent vantage point for observing these birds' roosting behavior.
To witness this annual phenomenon, birders gather in the schoolyard while it is still daylight, around 6:30 P.M. We get out of our cars, form small groups, and start looking up at the sky. Soon we begin to see a few birds, and hear their typical chitter. Then people begin to exclaim, "There's one!" "Here come six more!" "Did that one go down the chimney?"
When it is almost completely dark, we hear the swifts' chittering call grow louder and louder as they begin to assemble in larger numbers in the sky. Then, gradually, as it gets still darker, more and more swifts come from all directions to join them, and just before nightfall, tens of thousands are swirling about, first clockwise, and then counter-clockwise, above the chimney.
Slowly, and then faster and faster, they begin to funnel down the chimney. Once they begin this process, it takes only twenty minutes or so until the last chittering bird has disappeared. To perch, they cling by their toenails to the inside the chimney, using their stiff tails for support. They cover the inside of the chimney, overlapping one another like shingles. This ritual will be repeated nightly over a two or three week period, when, finally, the last swift will have left our area for the winter.
The chimney swift's scientific name is chaetura pelagica. Chaetura comes from the Greek root chaite, meaning "bristle"; and the Greek root oura, meaning "tail". Obvious enough. The derivation of pelagica is somewhat more complicated, since the word "pelagic" means "of or relating to the open ocean." Ernest A. Choate, in The Dictionary of American Bird Names, quotes Dr. Elliott Coues: "In 1758 Linnaeus named it Hirundo Pelagica, but in 1766 he changed the specific term to pelasgia. The Pelasgi were ... a nomadic tribe, and the implication of the term in ornithology is supposed to be the bird's migration, without any reference to the sea." At any rate, after a time, Coues reverted to pelagica once again, and that has remained the generally accepted scientific name, even though the chimney swift is most assuredly not a pelagic bird.
Although, to the uninitiated, swifts resemble swallows, especially in flight, they are related structurally not to songbirds at all, but to hummingbirds.
A chimney swift is capable of covering enormous distances during its lifetime. John K. Terres, in The Audubon Society Encyclopedia of North American Birds, writes: "A banded American chimney swift that lived for 9 years was estimated, during its lifetime, to have flown 1,350,000 miles, including round trips each year between the U.S. and South America."
Chimney swifts are remarkable little birds all around. According to Volume I of the Stokes Nature Guides, "More than any of our other common birds, the swift's life is lived on the wing." During daylight hours, they fly continuously. Just listen for their characteristic chittering sound, look up, and you'll see them swooping about as they hawk flying insects. They have small, weak legs, not suited for walking. If one does happen to land on the ground, it may have difficulty taking off again.
Swifts even conduct courtship activities while on the wing. They fly and glide with wings in a "V" formation, one bird slightly higher than the other. Sometimes they fly in threes. Some believe they may mate on the wing, but it is generally believed that mating takes place at the nest.
In areas of human habitation, chimney swifts select a high vertical surface, such as a chimney or a rough wall, upon which to construct their nest. In more rural areas, they can nest in hollow trees. In either case, they generally nest in colonies of two or three pairs.
The half-saucer-shaped nest itself consists of dead twigs. The birds, while in flight, collect these from bushes and trees. They attach the twigs to the surface, and make a nest of them by gluing them together with their own saliva. Sometimes the female begins to lay her 4 or 5 eggs before the nest construction is completely finished. Both parents share in incubation, brooding and food-gathering duties.
After about two and a half weeks, the young birds begin to leave the nest. At first they remain close by, and take only short flights close by the nest, still depending on their parents for food. After another two weeks or so they are ready to search for flying insects themselves.
In migration, chimney swifts forage for flying insects while on the wing. They fly all the way to their wintering grounds in Peru, northern Chile and northwestern Brazil without alighting anywhere to feed.
Enthusiastic birders, including me, travel all over the place to witness spectacular bird phenomena. We go to Bonaventure Island in Quebec to see nesting gannets, to Bosque del Apache in New Mexico or the Platte River in Nebraska to see wintering sandhill cranes, to the Pribilof Islands to see nesting puffins, and to hawkwatches along the north-south flyways to see thousands of broad-winged hawks in migration. Here in the Philadelphia area we think we're lucky to have our own bird phenomenon right here in our own neighborhood: thousands of migrating chimney swifts stopping by on their long journey south.
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