BIRD FLIGHT
Joel Zimmerman wrote in National Geographic, “As a feat of engineering, it’s hard to beat the flight feather of a bird. From the central vane sprout hundreds of filaments, some with grooves and some with hooks that zip the barbs together like velcro. They create a lightweight plane that can lift a bird into the sky. When the birds pull their feathers apart to clean them, the barbs simply zip back together by themselves.”
The flight mechanics of birds. In slow flight the down stroke of the wings occurs with the feathers compressed to produce lift. On the upstroke the feathers separate to allow air to pass through so the wing can return to upper position with a minimum of interference to flight.
After a flying bird — or flying insect or bat — makes a simple turns all its has to do to straighten out is start flapping its wings again. This finding was reported in an April 2009 in Science based experiments using high-speed film by a team lead by Tyson Hedrick of the University of North Carolina.
RELATED ARTICLES:
BIRDS: THEIR HISTORY, CHARACTERISTICS, COLORS factsanddetails.com ;
BIRD BEHAVIOR, SONGS, SOUNDS, FLOCKING AND MIGRATING factsanddetails.com
Websites and Resources on Birds: ; Essays on Various Topics Related to Birds stanford.edu/group/stanfordbird ; Avibase avibase.bsc-eoc.org ; Avian Web avianweb.com/birdspecies ; Bird.com birds.com ; Birdlife International birdlife.org ; National Audubon Society birds.audubon.org ; Cornell Lab of Ornithology birds.cornell.edu ; Ornithology ornithology.com ; Websites and Resources on Animals: Animal Diversity Web animaldiversity.org ; BBC Earth bbcearth.com; A-Z-Animals.com a-z-animals.com; Live Science Animals livescience.com; Animal Info animalinfo.org ; World Wildlife Fund (WWF) worldwildlife.org the world’s largest independent conservation body; National Geographic National Geographic ; Endangered Animals (IUCN Red List of Threatened Species) iucnredlist.org
Bird Aerodynamics
The body of a flying bird is streamlined like the fuselage of an aircraft. The feathers all point backwards from the head to the tail. The legs are drawn up like the wheels of an airplane. There are no protruding ears and sometimes the nostrils point backwards. Air taken in through mouth goes out the nostrils like exhaust.
Birds are very light. Weight-saving adaptions that allow bird to fly include hollow bones supported by internal struts like those that strengthen wings on planes; a bony beak rather than a jaw and teeth; tail feathers instead of a tail; and a skeleton that is fused together like a fuselage frame. Their feathers are mostly air.
All flying birds have lungs that extend into air sacs in the body cavity, filling space in the lightest possible. Most bird have nine of these air sacs: in the neck, chest, and towards the back of the abdomen. These serve not only as lighteners they also supply the bird with the extra oxygen they need for flying, which required a lot of energy.
Bird Feathers
Feathers are made of keratin, the same horny substance found in fingernails and lizard scales. They streamline the body, reducing friction and drag during flight, and are ideal for creating perfect airfoils, which give the birds lift n flight. Weight for weight, no devices has ever been produced by man or nature that act as a better airfoils. A bird’s colors come from both pigment and light reflecting structures in the feathers. A typical bird has 25,000 feathers.
Feathers have a central shaft with a hundred or so filaments on each side. Each filament is sided with a hundred or so smaller filaments or barbules. The barbules of flight feathers overlap and are hooked together so they create a continuous vane and give a feather its strength. There are several hundred hooks on each barbule and a million or so in a feather. Barbules that become unhooked are knocked back in place when a birds preens and strokes its feathers.
There are several different kinds of feathers. The two primary kinds are: 1) contour feathers, which are visible and help streamline a bird; and 2) down feathers, close to the body and found on chicks. Feather other than down emerge from tracts of skin called pterylae. Feathers are regularly replaced in a process called molting. Several birds have feathers that are toxic when touched or ingested.
Feathers are superb insulators, better than even fur. They are soft, fluffy and can trap air, keeping a bird warm and repel rain and water. Many water bird have down to keep warm. Unlike other feathers, down doesn't have a shaft with barbs. Instead branches come right out the skin. On cold days birds fluff out their feathers to stay warm. On hot days they flatten their feathers.
Feathers are also used to send a variety of other messages and identify species. During the breeding season some species such as bird of paradise's and cock of the rock's use their colorful feathers in courtship displays. Robert Clark, a New York City-based photojournalist and maker of the book "Feathers" told Smithsonian magazine a feather is “innately more interesting than other still-lifes. At one angle it might be purple, then you turn it and it’s green or blue.”
Feather Development
Bird feathers evolved from reptile scales. If you look at a bird embryo in its early stage of development you can see discs of cells called placodes scattered here and there. Some grow into scales like those that cover chickens. Others turn into feathers.
Research by Yale ornithologist Richard Prum suggests that feathers evolved in a series of steps, with old genes being borrowed for new uses. In reptiles specific genes mark off the front and back of each scale as it grows from the placode. In bird embryos each feather begins as a tube growing from a placode with the front and back genes at work in the feather evolution. Around 150 million years, ago, scientist estimate, these genes must have taken on a new role in dinosaurs causing some to sprout feathers and feather-like growths as seen in recent dinosaur fossils. [Source: Joel Zimmerman, National Geographic, November 2006]
Joel Zimmerman wrote in National Geographic, “The appearance of branch-like barbs was the next step in feather evolution, Prum argues, and the development of a baby bird’s downy feathers offers clues to how that happened. As a new feather tube grows, it is divided into strips, which eventually peel away into barbs. And once again, only a little tinkering with genes might have been required to get the tube to split. Prum has shown that the same genes that mark the front and back of reptile scales and feather tubes also mark the points around the tube where it will split.”
“Later, birds evolved the ability to turn these fluffy feathers into feathers with vanes, and then to lock the barbs together to make flight feathers, all with slight genetic changes...And by tweaking the growth of different parts of the feathers, birds evolved special plumage for hunting, swimming, courting and other activities.
Feather Care and Molting
Birds go through a great deal of trouble to tend and care for their feathers. Out of place feathers are repositioned. Ragged ones are restored with combing from the peak. Most birds have a large oil gland in their skin near their tail. The birds take oil with their beaks and use it to anoint their feathers and keep them water repellant. All this effort is rewarded with a more streamlined body and more perfect airfoils.
Fleas, lice and other parasites find feathers to be a warm cozy place to hang out. Many birds have parasite problem and constantly erecting their feathers and groom themselves to get rid of them. Some birds will even place ants and other insects in their plumage to get ride of parasites.
Feathers become damaged and wear out and need to be replaced. Most birds replace their feathers at least once year in a process called molting. Most species of bird molt over a long period of time, with a few feather replaced at a time so flying is not affected.
Molting usually takes in the spring or autumn. The old feather generally don't fall out until the new feathers emerge, so a bird can keep flying. This is not the case with many water bird who lose all their feathers at once and then grow new ones. Molting ducks are a sorry sight.
Bird Wings
The wings of birds developed from a single finger of their reptilian ancestors. The other finger have largely disappeared but most birds have the vestiges of ancestral thumbs as projections on the fore-edge of their wings which carries its own tuft of feathers.
Bird wings have curved leading edges and thin trailing edges that helps lift the bird the same way airplane wings lift a plane. Most birds take of by leaping into the wind and flapping their wings hard. They land by titling their wings at an angle to reduce speed and then throwing their bodies backwards and their legs forward.
The shape and sizes of wings allow different species of bird to do different things. Short, stubby, wings allow birds like tanagers to maneuver and swerve through the forest. Swept-back wings allow swifts and falcons to achieve great speeds while long extended wings of vultures and albatrosses allow them to glide and catch air currents. Fighter planes, supersonic planes and gliders follow the same principals.
The wings of a bird have more work to do than the wings of a plane. Not only do they have provide lift they must also serve as an engine. The muscles that operate the wings are the largest and strongest a bird possesses. The muscles that extend from wing joints to the deep keel on breast bone are the most powerful of all. They supply the power a bird needs to take off. The wing muscles of strong-flying birds such as pigeons account for half their total weight.
Wing Shape and Aircraft
Adam Summers, a professor of bioengineering at the University of California at Irvine, wrote in Natural History magazine ,’structurally the wing resembles your arm, remove or fuse a few bones, add some feathers, and you just about have it. When the wings flap as when your arms do, chest muscles power their motions.”
The structure of bird wings, which are essentially two featherbed airfoils, is crucial to flapping flight. “One airfoil is made up of primary fight feathers attached to the wingtip bones. The other is formed by secondary flight feathers attached to forelimb bones,” Summer wrote.
Bird wings change shape when they fly. The U.S. military tried to employ this idea into the F-14 Tomcat fighter, which has a “swing-wing” that changes shape depending on whether the plane is taking off or not and how fast it is going. The idea didn’t pan out — in 2006 the Tomcat was retired — and some said the problem was that wing shapes have quite different affects on stationary wings and flapping ones.
These days, scientists are studying swifts for insights into aircraft wing development in part because they don’t flap their wings much when they glide or dive. Swift wings resemble long, thin, curved blades that taper off at the end sort of like a scythe. They gain added maneuverability by having an unusually larger proportion of their wings made up of the “hand” or wing tip bones. By changing the “wrist” angle between the “hand” and forelimb, the swift can change both the shape of the wing and its area, thereby maximizing their efficiency at various speeds.
Wings of the Swift — One of the World’s Fastest Bird
Swifts are called swifts because their top flight speeds are so high. They have been clocked at over a 100 miles an hour and fall asleep at 20. The common swift (Apus apus) is one of the world’s fastest birds. It has a maximum horizontal speed 111.6 kilometers per hour (69.3 mph) and a maximum airspeed of 166 kilometers per hour (103 mph). Adam Summers wrote in Natural History magazine: Swift wings, compared with those of typical birds, have proportionately large wingtip bones, giving added maneuverability in flight. By changing the angle between the wingtip bones and the forelimb bones, swifts alter the shape and area of their wings, thereby maximizing their efficiency at various speeds. [Source: Adam Summers, Natural History magazine, March 2008]
Swifts belong to the family Apodidae, which literally means “without feet” in Latin. Footless may be a bit of an exaggeration, but it’s pretty near the mark. The birds’ tiny feet seldom touch down because feeding, courting, and even sleeping all take place on the fly. Because swifts glide for long distances—without complicating things for observers by flapping their wings—and because they change the geometry of their wings in flight, they make an ideal bird with which to study the advantages of wing morphing.
Overall, the swift wing resembles a long, thin, curved blade that tapers to a sharp point, much like that of a scythe. Structurally, the wing closely resembles your arm: remove or fuse a few bones, add some feathers, and you just about have it. When the wings flap, as when your arms do, chest muscles power their motion.
In essence, those sets of bones give swifts, and all flying birds, two feathered airfoils on each wing, crucial to flapping in flight. One airfoil is made up of primary flight feathers attached to the wingtip bones. The other is formed by the secondary flight feathers attached to the forelimb bones. The swift, however, gains added maneuverability by having an unusually large proportion of its wing made up of the “hand,” or wingtip, bones, compared with typical birds. By changing the “wrist” angle between the “hand” and forelimb, the swift can change both the shape of the wing and its area.
David Lentink, a biomechanist at Wageningen University in the Netherlands, and a team of aerodynamicists from the Netherlands and Sweden measured swift wings in a range of natural flight configurations. One of the most important factors, they discovered, is the aforementioned angle between the hand and the forelimb. Folding the wrist knocks a whopping 30 percent off the wing area.
Lentink and his colleagues also attached wings (from birds that had died in sanctuaries) to a finely calibrated balance in a wind tunnel, to measure how various wing geometries alter drag and lift. Drag is the force that acts in the same direction as the airflow, whereas lift acts perpendicular to airflow. Drag and lift, along with a bird’s mass, determine the biologically important variables of gliding flight. For swifts with unfolded wrists and outstretched wings flying in a straight line, Lentink and his colleagues determined that a speed of about twenty miles an hour gives the birds the maximum gliding time and the steadiest flight path for the least energy. So even though outstretched wings provide more drag, the wide spread gives a lot more lift for level flights.
If straight-line flying benefits from spread wings at lower speeds and swept wings at higher speeds, what about turning?. Keeping the spread-wing shape when turning is also a good strategy for the swift—at least at twenty miles an hour. At that velocity, a swift can turn at least twice as fast by spreading its wings as it can by bending them. In higher-speed turns, however—as simulated in the wind tunnel—it becomes impossible to measure the relative efficiency of spread and swept wings, because beginning around thirty-four miles an hour, spread swift wings become vulnerable to damage from aerodynamic stress. At high speeds they naturally flex and twist slightly in the turbulent air, and so avoid being damaged by the high forces. So, when pursuing fast-flying and fast-turning insect lunches, a swift bends its wings to keep up; the calories from such a meal warrant the extra effort.
25-Million-Year-Old Bird had a Wingspan Over Seven Meters
The wandering albatross has the largest wingspan of any bird alive today, extending almost 3.5 meters (12 feet). But that’s nothing compared to the wingspan of the Pelagornis sandersi, whose fossils were unearthed in South Carolina. It lived 25 to 28 million years ago and had largest-known avian wingspan ever known, about 6.1 to 7.4 meters (20 to 24 feet). [Source: Will Dunham, Reuters, July 8, 2014]
Will Dunham of Reuters wrote: Size alone did not make it unique. It had a series of bony, tooth-like projections from its long jaws that helped it scoop up fish and squid along the eastern coast of North America. “Anyone with a beating heart would have been struck with awe,” said paleontologist Daniel Ksepka of the Bruce Museum in Greenwich, Connecticut, who led the study published in the Proceedings of the National Academy of Sciences. “This bird would have just blotted out the sun as it swooped overhead. Up close, it may have called to mind a dragon.”
With its short, stumpy legs, it may not have been graceful on land, but its long, slender wings made it a highly efficient glider able to remain airborne for long stretches despite its size. It belonged to an extinct group called pelagornithids that thrived from about 55 million years ago to 3 million years ago. The last birds with teeth went extinct 65 million years ago in the same calamity that killed the dinosaurs. But this group developed “pseudoteeth” to serve the same purpose. They lived on every continent including Antarctica. “The cause of their extinction, however, is still shrouded in mystery,” Ksepka said.
Image credit: Liz Bradford
“All modern birds lack teeth, but early birds such as Archaeopteryx had teeth inherited from their non-bird, dinosaurian ancestors. So in this case the pelagornithids did not evolve new true teeth, which are in sockets, but rather were constrained by prior evolution to develop tooth-like projections of their jaw bones,” said Paul Olsen, a Columbia University paleontologist who did not take part in the study.
These birds lived very much like some of the pterosaurs, the extinct flying reptiles that lived alongside the dinosaurs that achieved the largest wingspans of any flying creatures, reaching about 36 feet (11 meters). Its fossils were found in 1983 when construction workers were building a new terminal at the Charleston International Airport. Its skull is nearly complete and in great condition, and scientists also have important wing and leg bones, the shoulder blade and wishbone.
Until now, the birds with the largest-known wingspans were the slightly smaller condor-like Argentavis magnificens, which lived about 6 million years ago in Argentina, and another pelagornithid, Pelagornis chilensis, that lived in Chile at about the same time. At about 48 to 90 pounds (22-40 kilograms), Pelagornis sanders was far from the heaviest bird in history, with numerous extinct flightless birds far more massive.
Image Sources: Wikimedia Commons
Text Sources: Mostly National Geographic articles. Also David Attenborough books, Live Science, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
Last updated November 2024