New fact for me:
The roosting habits of swifts are mysterious. Except when, as adults, they crawl inside holes in buildings to breed, the species stays permanently aloft - both night and day. The birds sleep on the wing but how do they avoid collisions and preserve a safe cruising altitude? Despite being an abundant summer visitor throughout the Northern Hemisphere their nocturnal behaviour has been little studied. However, in Suffolk in 1994 several hundred were watched just after dawn. Instead of flying and gliding around in the usual rapid manner, each maintained a stationary position on gently flapping wings. Basically, the birds were hovering and did so for almost an hour until the air warmed up and normal feeding flight resumed. This observation explained why radar research aimed at unravelling their actions failed to detect what they did. By moving very little, the birds rendered themselves invisible - truly, the world's first stealth aircraft.
Then came the Swedes. In 2000, using infra-red photography, they filmed swifts roosting like bats. Hanging by their toes the birds spent the night suspended on willow branches. The mystery just got deeper!
http://www.bbc.co.uk/nature/animals/birds/weeklyfeature/sleepingbeauties
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Scene One: It's Saturday afternoon. The day had begun with rain, but it's clear now and the residents of West Lewis Street in Hillcrest/Mission Hills area are outside enjoying the sun and crisp air.
Suddenly, a "huge flock" appears overhead. (Enter with great drama.) Hundreds of small, dark birds with long, stiff wings and slightly rounded tails begin to wheel and somersault en masse, at times just 25 feet or so off the ground, barely making a sound.
Then they swoop in, diving like airborne lemmings down the chimney of one of the homes. The house is for sale. Everybody thinks the owner is away, but moments later, Nat comes running out, wide-eyed, wondering, says neighbor Suzanne Dukes, whether he's "on acid or what?"
"It was a Tippi Hedren moment."
Scene Two: Nobody knows what to do next, until they begin to see birds smacking into windows, attempting to exit. Nat, the homeowner, runs back inside to frantically open windows and doors. Some birds fly out, but many more remain clinging to walls and curtains. Nat starts picking them up and carrying them outside, where they fly off.
"I took a few," said Dukes, "and to my surprise they were sleeping in my hands - eyes closed. For about a minute or so, I looked at one of them. Only after I blew on one did he open his eyes and fly off. They were very tired."
Sometime later, the rest of the flock rouses itself. Most of the birds had remained in the chimney, snoozing. They billow out of the chimney like smoke and disappear, leaving only a houseful of soot behind.
Dukes thought the birds were chimney swifts, which get their name from their preferred place for breeding and roosting. She's close. Chimney swifts (Chaetura pelagica) are a common sight in the eastern half of the United States, but very rare here. The visitors to West Lewis Street were Vaux's swifts (Chaetura vauxi), a closely related species that prefers forest accommodations but will apparently settle for a suburban tract home when a hollowed out redwood or fir isn't available.
The swifts stopped by while en route from Mexico and points farther south (where they winter) to nesting sites in the old growth forests of the Pacific Northwest. It's a long migratory flight, and the birds get tired, said Phil Unitt, an ornithologist at the San Diego Natural History Museum and editor of the journal Western Birds.
"They were looking to roost overnight," Unitt said. "If nobody had bothered them, they would have left the next morning and nobody would have been the wiser."
Obviously roosting in chimneys and other urban locales poses a distinct danger to the swifts. A few years ago, Unitt said a flock dove into navy base boiler and were collectively cooked. To avoid such a fate, he encourages San Diegans to close their chimney flues in early April, or keep chimney openings suitably capped.
http://www.signonsandiego.com/uniontrib/20040428/news_1c28singular.html
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In every bird book I look at, claims are made that swifts do almost everything in the air, including mating and sleeping. How is this known? If it is from monitoring behavior at the nest, how can one be sure the swifts aren't secretly performing these behaviors somewhere else? -- Barry Drees, Oftersheim, Germany
The swift family consists of about 80 species worldwide. The family name, Apodidae, means "without feet." Swifts do have feet, of course, but the birds spend so much time in the air that their feet have evolved into tiny extremities. Swifts can barely walk but do have strong claws, which they use to cling to vertical surfaces. Called "flying cigars," swifts can log more than 500 miles in the air on a single day during the breeding season.
Swifts are so well adapted to aerial life that most normal functions are carried out on the wing - foraging, eating, drinking, bathing, courtship, gathering nesting materials, and yes, mating. Copulation is rarely complex or long lasting; it consists of a few seconds of contact between the male and female bird's cloacas, the all-purpose passage for waste and reproductive materials. For aerialists as accomplished as swifts, this is not hard to accomplish while flying. Swifts do, however, also mate at the nest site. For North American Chimney Swifts, this is the more frequent site of copulation. As for sleeping, swifts do so at a roost site, often in large groups inside a chimney or similar structure, a cave, or a hollow tree, depending on the species.
You are correct that much of what is known about swifts comes from observations made at the nest, as well as at roost sites, since these are the only places swifts are "grounded" enough for humans to study them.
For excellent information on establishing and maintaining swift nest sites, contact the North American Chimney Swift Nest Site Research Project, developed by the Driftwood Wildlife Association, Texas Parks and Wildlife, and Texas Partners in Flight. See "Learn More" in our February 2003 issue (p.84) for contact info. The article "The Bird in Your Chimney" in the same issue (p.36) contains more on Chimney Swifts.
http://www.birdersworld.com/brd/default.aspx?c=a&id=214