Secrets of flocking revealed
While the actions of one particular bird or species do not necessarily mimic the aggressive behaviors such as tail fanning, this behavior means "Back Off!". make their presence known to other birds, or possible to re-establish relationships . is leaning forward with quivering or flapping wings is getting ready to take flight. Hiding A bird that doesn't want to be put back into the cage might hide at the back of the . away their beloved when another bird, a threat to the pair, flies into the territory. The “jealous” bird is simply protecting their mate and their relationship. The RSPB wants to bring back the colour to the roadsides of East Riding by returning verges to . How do birds manage to fly so closely together without colliding, and what are the The Greek word 'allelo' describes mutual relation to one another, and Bar-tailed godwits Limosa lapponica, flock at high tide, Firth of Forth.
The ostrich, the emu, and the kiwi run very fast. The penguin swims with its short paddlelike wings. None of them can fly. All birds, however, have featherswhich no other living animal has, though paleontologists have found fossilized remains of a few dinosaurs and other reptiles—probably the ancestors of birds—that appear to have had feathers.
Birds are feathered, warm-blooded animals with backbones. They have two legs.How Do Birds Fly?
Whether they fly or not, all have a pair of wings corresponding to the arms or the front legs of many other animals. A beak takes the place of a jaw with teeth. All birds lay eggs.
Most of them build a nest in which they care for the eggs and the young birds. A robin or a chicken in a rainstorm will stand with wings and tail drooping to the ground.
The water simply slides off without soaking through. On a cold winter day the bird fluffs out its feathers. In hot weather it flattens the feathers close to its body. When they are fluffed out they hold a layer of warm air next to the skin. When they are flattened they keep the skin cool by preventing hot air from reaching it. The three types of bird feathers A feather has a main shaft that is stiff and solid.
Barbs branch from the shaft and together compose the vane. Each barb in turn branches into smaller barbules. Tiny hooks, or hooklets, on the barbules lock all the neighboring barbules together. When a feather is ruffled the wrong way the hooks tear apart. When the feather is smoothed the hooks relock like a zipper. Contour and down feathers The body feathers are called contour feathers. The big wing feathers are well zippered to make the wing strong and stiff.
Some contour feathers are for show only. These are the plumes that some male birds display during courtship. Ostrich plumes and the long back and breast feathers of the egret are soft and fluffy.
This is because the barbs do not have hooks to hold them together. Showy feathers do not need to be strong. Beneath the contour feathers there is often a thick coat of down. Down feathers have no shafts. The barbs branch from the hollow part that fits into the skin, and there are no hooks. Water birds have extra-thick coats of down. That is one reason why the ducks we see in wintertime paddling about in icy water are not cold.
The first feathers on a newly hatched chick are usually down feathers. Pinfeathers are familiar to anyone who has watched a chicken or a turkey being cleaned for cooking. The stiff black prickles are coverings to protect the tender new feathers. As the feathers develop, the coverings split and peel off.
Care of the feathers Birds keep their plumage clean and neat. When the feathers are ruffled by the wind the birds smooth them with their bills. They run the bill over and under the wings and tail and along the back. This combing of the feathers is called preening. Another purpose of preening is to spread oil over the feathers. Most birds have a pair of oil glands on the back, just above and in front of the base of the tail. The bird presses out the oil.
Then it runs its oily bill all over the feathers. It cannot reach the head feathers with its own bill of course, so it rubs its head against its body to oil the head feathers. All birds like to bathe. Some even take dry baths in dust, sand, and snow. Such bathing may help get rid of lice in the feathers. Their behavior as they do so reminds one of a cat rolling and playing in catnip leaves. They twist into awkward positions, trip over their feet, and get so excited that they step on their own tails and fall over backward.
More than species of birds have been reported to use ants in such a manner, including the blue jay and common grackle. Why birds do this is unknown. One explanation is that the formic acid produced by ants may reduce external parasites and may soothe skin irritation that can accompany the growth of new feathers. Colors and patterns of feathers Every species of bird has its own color and feather pattern. The male and female may look very much alike. The female robin has a brown head and paler breast but otherwise looks like the male.
In many species, however, the sexes differ. Usually the male is more brightly colored. An exception is the phalaropea kind of shorebird. The female is the more colorful sex. In this species, the males incubate the eggs and care for the young.
The dull color of most females permits them to remain camouflaged, or protectively coloredand unobserved on the nest. The streaked dark feathers of the female red-winged blackbird blend perfectly with the brown of the nest fastened to the stems of cattails in a marsh.
The male, with flashing red and yellow shoulders, perches on top of a cattail some distance away from the nest, drawing all the attention to itself and away from the eggs and young. In the families of birds that nest in holes—for example, the woodpeckers and kingfishers —the females are almost as bright as the males.
They do not need to be camouflaged because they and the nest are out of sight. Changing old feathers for new Feathers wear out, as clothes do, and need to be replaced. This change is called molting.
All birds molt all their feathers at least once a year, in summer or early fall. Most birds shed only one pair of feathers at a time from wings and tail.
The feathers always drop in a definite order. A second pair does not fall until the new pair is almost fully grown. Thus the bird is never handicapped in flying. Ducks, geeseand some other water birds are exceptions. Their flight feathers fall all at once and they are unable to fly. But because they swim, they can find food and hide from their enemies around the edges of waterways. Brightly colored male birds may have two molts.
In the fall and winter they resemble the dull females. In the spring they acquire their brightly colored breeding plumage.
Again, many of the waterfowl are different. These birds begin to get a dull plumage by early June. They wear it when they need protective coloration—during the period when they cannot fly.
Then when their new flight feathers have grown in, the body feathers molt again. By late September many species, such as mallards, are once more in their bright breeding plumage.
Some birds change their colors without molting by a process called feather wear. This occurs if the new feathers are edged with brown or gray. The overlapping edges hide the underlying main color of the feathers.
Snow buntings change from brown in the summer to white in the winter simply by wearing off the rusty edges of their white feathers. Often some prominent mark is hidden in this way during the winter. For example, the black throat patch of the male house sparrow is a narrow spot all winter. By May or June the feather edges have worn off and the throat is black.
Purple finches change from brown to rosy red by wearing off the brownish barbules. Molting requires energy, and during that time birds remain very quiet. They do not sing or display themselves. Late summer is the hardest time of the year to study birds because they are so difficult to find. Once the molt is completed, they regain the energy they need for migrating or for facing the hardships of winter.
A Feathered Flying Machine A flying bird is streamlined like a jet airplane, with its body slender and tapering, but birds are proportionally lighter than planes. All the feathers from head to tail point toward the back of the bird. The wings have delicately curved leading edges and thin trailing edges. The legs of many birds can be drawn up under the body. There are no projecting ears on the head. Even the nostrils in some birds point toward the back of the bird.
The air comes out of them like the exhaust from a jet, moving to the rear. The bones of a bird are light in weight. Many of them are hollow and filled with air. In large soaring birds some of the hollow bones have internal braces like the struts in airplane wings. Instead of a jaw, with heavy bones, teeth, and muscles, a bird has a slender beak. The work of chewing is done by the crop, in which preliminary food breakdown occurs, and by the gizzard, a part of the stomach where food is ground up.
Certain bones that are separate in other backboned animals are joined together fused in birds to give them greater strength. Some of the bones have high ridges for the attachment of muscles. The keel on the breastbone is an example. The ribs are long, flat, thin, and jointed. Each rib overlaps its neighbor. Together with the backbone and the breastbone the ribs form a flexible cage that holds the heart, lungs, and other organs and makes a strong base for the attachment of the powerful wings.
Air Sacs for Lightness and Cooling In addition to having lungs, birds have five or more pairs of air sacs. They are connected to the lungs by small tubes. Branches extend into the hollow bones.
The bones of the skull, and sometimes even the small toe bones, are air-filled. The air sacs not only lighten the body but also serve as a cooling system. Birds do not perspire. A constant stream of fresh air flows all through the body by means of the air sacs. Birds probably never get out of breath.
The wing strokes press in the rib case to expel stale air. Hence the faster they fly, the faster the wing muscles pump air and the easier the bird breathes. The muscles that operate the wings are the heaviest part of the body. In such swift birds as pigeons they account for as much as one half of the total weight. The muscles are attached to the keel, or center ridge, of the breastbone.
These big flight muscles form the breast meat of the birds eaten by humans. The neck of a bird moves more freely than that of any other animal. This is because it has more vertebrae, or sections of the backbone. The sparrow has 14 vertebrae in its neck. A giraffe or a human has only seven. A flexible neck permits the bird to look in all directions for danger, to catch food more easily, and to preen its feathers.
Birds are warm-blooded animals, like human beings. They live at a much faster pace, however. Flying takes a great deal of energy, and all their life processes are speeded up. The body temperature of a bird is higher than that of most other animals. The swift has a temperature of The human heart beats, on average, 72 times a minute.
Because of their high rates of metabolism, birds burn up calories very quickly. Small birds must eat almost constantly during the daylight hours. An American kestrel hovering feet 30 meters above a field can spot a grasshopper and drop directly on it, keeping it in focus all the way to the ground.
Birds can change the focus of their eyes for different distances much more quickly than can other animals. They look straight forward with both eyes together, so that they have binocular vision. The eyes of most birds, however, are located at the sides of the head, and they have only monocular vision. Birds cannot move their eyeballs. For a bird with monocular vision to see a nearby object directly in front of it or to watch something moving, it has to turn its head.
Besides the upper and lower eyelids, birds have a third eyelid—called the nictitating membrane. It is transparent and moves from side to side instead of up and down. It keeps the eye moist and protects it from dust. The nictitating membrane protects the eyes of owls from strong daylight and permits eagles to look into the sun.
Scientists at Cornell University have conducted experiments to find out what birds hear. In one such experiment, captive house sparrowsstarlingsand pigeons were trained to feed from a tray that was wired with electricity.
At the same time they struck a note of a known number of vibrations per second. After a time the birds would jump when the note was struck even though there was no shock. This is known as a conditioned reflex test. The notes were raised and lowered until the birds did not jump because they could not hear the note. Thus it was learned that birds in general have a narrower range of hearing than human beings.
Middle C on the piano has a frequency of vibrations or cycles per second. Starlings and sparrows cannot hear middle C at all. Pigeons can just barely hear it. Horned owls cannot hear below 70 vibrations per second. Thus ruffed grouse can safely drum at night in woods where these bird-eating owls live. The drumming of the grouse, at 40 cycles per second, cannot be heard by the owls. Experiments have been conducted with these birds to find out if they locate their food by smell or by sight.
Vultures are believed to recognize dead animals by sight but also to some degree by smell. However, in most birds the sense of smell is of minor use. A favorite food of the great horned owl is the skunk.
Most birds seem to select their food by its familiar appearance, sound, or touch, and not by its smell or taste. The Language of Birds The vocal organs of a bird are somewhat different from those of humans. Instead of having vocal chords in the larynx at the upper end of the windpipe, it has simple membranes that vibrate.
The membranes are located at the lower end of the windpipe in a structure called the syrinx. The shape of the syrinx and the number of muscles that control the tension of the membranes vary with the different families of birds and produce the different songs. Certain thrushes are recognized as having beautiful songs and can actually sing in chords of several notes at once. Thrushes that can do this include the hermit and wood thrushes of North America and the European nightingale.
The Purposes of Bird Songs In general, bird songs serve two main purposes—territorial claims and courtship—although caged birds apparently sing from boredom and inactivity. A male bird will perch on some prominent place, such as a weed top, telephone wire, or tree branch, and sing lustily to inform other males of the same species that a certain territory belongs to it. The basic pattern of a song is inherited.
Its finer details are learned from the parents and other adult birds. A bird raised in captivity without hearing the song of its species develops only a simple approximation of the wild song. There are food calls, danger calls, calls to let their mates and young know where they are, and calls to keep the flock together during migration.
Baby chicks become immobile when the mother hen gives a warning note; the shadow of a hawk overhead means danger to the mother, who produces the danger call. The young recognize it and respond with the proper behavior. The chickens of Illinois and the chickens of Europe communicate in exactly the same language.
Such social birds as the crows, ravens, and European jackdaws, all members of the highly intelligent Corvidae family, have a great variety of signals that give many kinds of information. How Birds Fly Humans have long been studying the flight of birds and trying to imitate it. Not until the 20th century did engineers fully understand the principles of flight that birds have been using for millions of years. The wing feathers most important in pushing a bird forward are the primaries.
They are attached to a single bone that corresponds to the first and second fingers of a hand and the fused hand bones. The secondaries are the feathers of the inner wing. They are attached to the lower arm bone.
They play an important part in supporting the bird in the air. The primaries and secondaries can be used separately.
Attached to the upper arm bone are the tertiaries. Each wing feather overlaps the one next to it, starting from the base of the wing outward. On the downstroke of the wing the air pressure on the underside forces these feathers into an airtight fan. Speed and forward motion are gained. On the upstroke the wrist joint is bent, and all the primaries and secondaries turn on edge, like the slats of a venetian blind.
Thus the wing is lifted with the least wind resistance. Slow-motion pictures show that as the wings move downward, forward, then quickly upward, the wing tips move through a figure-eight pattern. In addition to forward flying, birds soar and hover. Soaring means gliding on wind currents. Hawks and seabirds soar when they are looking for food below them.
Hovering means hanging in the air over the same spot with the tail lowered and outspread and the wings fluttering rapidly. Most small birds take off with a quick upward leap into the wind and strong fast wing beats. Dabbling, surface-feeding ducks also jump directly from the water.
The wings The movement of the wing, although controlled by the muscles, is governed by the bones and the joints that articulate them. In the case of the bird wing, the free movement around the joint of the wrist is curtailed so that there is only movement in one plane, preventing the wing from bending up or down during the forces exerted by flight. In birds the elbow and wrist joints are linked so that extending the elbow automatically extends the wrist.
This is possible because unlike in the elbow of humans, in the bird wing both the ulna and the radius have their own condyle point of articulation on the distal end of the humerus. The ulna is more distal to the radius on the elbow so that when the elbow is flexed the two bones of the forearm oppose one another.
The radius is then pushed into the various carpal bones of the wrist whilst the ulna is withdrawn. This automatically makes the wrist, and thus the hand flex too and the wing is folded. During extension of the wing the opposite movement occurs. In this way the wing is controlled by the flight muscles, decreasing weight and simplifying coordination.
Understanding birds & weather: Fall birding basics - eBird
The wing is the lifting surface of the bird and as such must have the right shape and profile to provide the airflow to produce this lift.
Much of the visible shape of the wing is produced by the covering of feathers, however, there is a narrow flap of skin that is called the propatagium.
This is stretched tight along the leading edge between the shoulder and the wrist when the wing is held out. This is an important part of the wing, it is covered in feathers and forms the leading edge of the inner wing where it helps to provide much of the lift developed by the wing.
To provide it with the required rigidity against the airflow the bones of the wing tend to run nearer the leading edge, whilst the trailing edge is constructed solely of a rigid line of feathers. Covert feathers also cover the entire wing and at the trailing edge are found the much larger primary remiges and secondary feathers secondary remiges The alula is formed by digit II, and lies almost at the wrist joint on the leading edge of the wing.
It acts in a similar fashion to the slots on an aircraft, naturally raising into the airstream when the wing approaches stall. The alula is prominent in birds such as the corvids and almost absent in some soaring seabirds. The legs The legs of a bird may not be considered to be an important requirement for flight, however, without the power they provide during take off many birds would be unable to become airborne.
The same can be said for landing where the legs are often used to absorb the large amounts of energy that are generated during initial contact with the ground. Starlings and pigeons do not run to gain speed, instead they jump into the air.
This jump is powerful enough to supply the initial inertia required to get them fully airborne. Once in the air they are able to use the full movement of their wings to continue their skyward motion. Albatross with their long wings and swans with their high wing loadings normally rely, like aircraft, on increasing their momentum on the ground until they reach a speed that allows them to become airborne, whilst some dabbling ducks, such as the mallard, are able to launch themselves vertically into the air straight from the water, an incredible feat of pure power.
The tail The wings are not the only lifting surfaces found on birds, the tail also plays an important role in flight. Obviously tail types vary greatly within the birds and some tails are used for display as well as for flight, but like the wing, their shape is often influenced by their lifestyle.
The wings of a bird generally lie slightly ahead of the centre of gravity, this means that when a bird flies its posterior trails in the airflow behind it. The tail provides not only the lift required to buoy up the weight of the body but it also helps in flight control, unfortunately it also adds to drag at higher speeds. The tail allows the wing design in birds to be tailored for efficient cruising and high speed flight and under these conditions it is furled to provide minimal drag.
At lower speeds, however, or during maneuvers the tail can be quickly unfurled to reduce induced drag see later from the wings and provide a surface for enhanced steering, lift or braking.
The tail is suspected to play an important part in maintaining balance and stability in flight and it would seem that it is required to generate lift at low speed when the interaction between the wings and the tail can also most effectively reduce drag. The retrices, or tail feathers generally numberbut are found to range between 8 and These are normally straight and bilaterally paired and the bases covered by coverts to produce a smooth surface for airflow.
When you look at a birds tail you see the retrices which are controlled by the tail muscles that allow for the various movements that are required for precision flying.
The feathers Feathers make an ideal aerodynamic surface for airflow. They can produce a smooth uninterrupted surface over which air can pass freely and can remain flexible without losing their aerodynamic properties. Further to that, the surface is also somewhat malleable, giving under areas of pressure, thus letting air pass more easily over the body without disrupting flow and causing drag.
Flight feathers are asymmetrical, with the leading edge vane being narrower, thicker and less flexible than the trailing edge. If the leading edge of the feather was to bend excessively in the airflow it would cause twisting of the feather, leading to a damaging loss of lift. This asymmetry, however, also ensures that the trailing web of the feather bends upward during the downstroke, providing forward momentum and lift.
This is probably to property that helps them withstand the larger aerodynamic forces that these feathers are subjected to. Sources for this section: University of Wales, Aberystwyth: Again, most of this section comes from a serie of on-line lectures given at the University of Wales, Aberystwyth http: From them I've selected and made some editing to those parts that were potentially useful for my model.
Check the original site for further information. Now a birds wing, when outstretched into the air, is held at a slight downward angle to the onflowing air. This means that air passes over the wing faster than it passes under the wing so there will be less pressure above the wing and more pressure below. This change in pressure causes the wing to move toward the lower pressure with a helping push from the higher presssure below it, thus causes lift. The faster air moves across the wing the more lift the wing will produce, so moving it through the air by flapping increases this airflow and thus increases lift.
The wing Drag Air causes drag on a flying bird and it is this drag that is often important in deciding the shape, not only of the wings but also the body and tails of the bird. It has to be remembered though, that without drag, caused by the movement of air across the wing, it would not be possible to gain any lift, so a zero drag situation is not only out of the question, but it would also be highly undesirable.
The first thing to note about drag during flight is that for experimental purposes it can be subdivided into three main categories and so we find parasite, profile and induced drag being produced. Parasite drag is the drag produced by the flow of air over the body of the bird and like a car this is influenced by any uneven surfaces or jutting protrusions such as legs.
Remember that drag increases with speed and as herons fly much more slowly than ducks or geese this aerodynamic requirement comes secondary to the functional requirement of food gathering.
It is here that air bleeds off the body and the potential for a great deal of energy sapping turbulence is produced. Most birds have a tail that helps the flow of air leave the body and can be used to increase lift if required. That is why swallows, frigatebirds and an number of other fliers have sharply forked tails and why falcons and nightjars have very narrow ones.
The production of lift comes at the expense of an increase in drag, this is termed induced drag. When a wing producing lift passes through the air it leaves circulating air in its wake that represents lost kinetic energy, thus induced drag is the product of lift production and does not include profile drag which we will come to shortly. When calculations of induced drag are made they assume that air has no viscosity, which we all know to be incorrect. Profile drag takes into account the viscosity of the air so that the addition of profile drag values to those of induced give the total drag value of the wing.
Profile drag is in effect what it sounds like, that is the drag produced by the profile of the bird as it moves through the air. So if we add the profile drag, the parasite drag and the induced drag together we find the figure for the total drag.
Its not only the wings that add to induced and profile drag though, the tail can also act as a lifting body thus causing induced drag. At the same time, because it is unfurled, it will also add to the profile drag too. Angle of attack The angle of attack of the wing is one of the main factors that affects the amount of lift produced, it also has important implications on the amount of drag that it develops.
The angle of attack is the angle at which the leading edge cuts into the forward flow of air and around degrees is often quoted as being the norm. Increasing this angle increases the volume of air diverted over the wing and leads to an increase in lift, but this is at the expense of drag which quickly increases. This can be demonstrated easily by holding your hand out of a car window as it is being driven along.
If you hold your hand flat and then gently rotate it into the oncoming airflow you should feel a gradual increase in lift until finally when you turn it too far it will suddenly lose all its lift and your hand will be jerked backward by the airflow, this is called a stall and is due to the loss of a smooth airflow over your hand.
A bird can obviously adjust this angle of attack, not just simply by rotating its wing but also by changing the attitude of its entire body with respect to its forward motion. So during slow flight birds and aircraft tend to fly nose up with a fairly high angle of attack, whilst traveling at speed they tend towards nose down, producing a much lower angle of attack. During take off, when there is very little airflow over the wings, birds such as pigeons increase the angle of attack to give the wing greater purchase on the air so that a larger amount of force can be generated.
During a stoop on the other hand a falcon will minimize the angle of attack to allow it to slip through the air with a minimum of drag. The shape of wings have also evolved to help produce lift from lower angles of attack. This is accomplished by the use of a cambered wing. Thus the birds wing is not flat in section, but instead is concave.
Because of this the leading edge attacks the air with a lower aspect it faces straight on into the airstream than the trailing part and thus minimizes drag, bringing with it the bonuses of better stall and lift characteristics. The aspect ratio of a wing is important as generally the higher the aspect ratio longer and narrower wings the lower the induced drag produced by the wing at a given speed. Wings with a high aspect ratio tend to be found on birds that soar at relatively high speed whilst those with lower aspect ratios shorter, wider wings are found on birds that soar at lower speeds.
Drag is produced when high pressure air passing under the wing swirls upward into the low pressure area above and behind the wing. As it does the air creates a sheet of eddies that disrupts the movement of air across the wings trailing edge.
This phenomenon reduces lift and leads to drag creating turbulence which is most pronounced at the wingtip, where it is called the tip vortex. This phenomena can often be seen in aircraft where vapour trails can be seen emanating from the wingtips, especially during hard maneuvers. This effect can be diminished by increasing the length of the wing and so decreasing the tip to wing length ratio.
Incidentally it is this tip vortex that is used by gulls, geese etc when they fly in the V type formations that you often see.
The air directly behind the wingtip is the rising part of the vortex and it is this that the formation flying birds exploit. To get the best out of it they must be tucked in closely behind the leading bird or they will fly into the downwash. In this manner they can minimize their energy usage.
Many birds have a requirement for shorter wings and so another method of dissipating tip vortex has evolved. In aircraft, vertical winglets are often placed at the end of the wing to dissipate these vortices in a vertical plane.
Birds use a similar method, although in this case their winglets are formed by the primary feathers of the wing. This design of wing is often termed, slotted, meaning that there are gaps between the feathers so that each feather acts independently. As I say, this is most pronounced at the wing tip, where, if you watch a bird in flight you will see these feathers bending upward as the air from below the wing gushes up into the low pressure above.
This bending of the feathers leads to the displacement of the tip vortices to the vertical dimension, thus spreading it across a greater area of the wing, leading to a decrease in induced drag. It also leads to the production of forward momentum. To understand a little more the important implications of wingspan and aspect ratio on flight, imagine a bird soaring in level flight through the air at a given speed.
Now take a snapshot of 1 second of that birds flight. Looking from directly above the bird you could measure the area that it has passed over by measuring the span of the bird by the distance covered in that second. If the bird has a long wingspan the area will be larger than that of a bird with a lesser wingspan. The measurement that you get can be correlated to the amount of air that that bird has passed through in that given time frame.
From this we can see that a bird with a longer wingspan is able to move through more air than a bird of shorter wingspan. Now if that bird is gaining its lift from the air that it has passed through we can also see that a bird of the same weight, with a smaller wingspan, will have to gain more lift from that air than the one with a longer wingspan.
In other words the bird with the shorter wingspan has to move more of the air produce more lift from a given amount of air that it passes through to obtain the lift that it requires to keep it airborne. It is not only the length of the wings that affect the flight characteristics of the bird, so does the chord length or width of the wing. The longer the chord length of the wing, the greater the separation of the air over its surface can be.
So birds with wide wings are generally able to derive more lift from the air they pass through than birds with narrow wings. It has been found in the Procellariiforms petrel and albatrosses and it is probably a general phenomenon with a number of bird families, that there is a tendancy for larger birds to have the higher aspect ratio wings.
Wing loadings have an important implication on large birds and explains why there is a limit to their size. As a bird increase in size, its volume, and so its mass will increase by the cube root, whilst the wing surface only increases as a square root, this is often termed scaling. As the bird gets larger its wing loading will increase until it reaches a value that cannot be sustained.
The vultures, albatross and swans are very large birds, at the extreme end of the size scale and have solved the problem of size in different ways. Neither the vulture or the albatross is very proficient at powered flight and both birds rely heavily on their environment to produce the lift they require to both take off and to stay in the air.
The vulture though, uses high lift wings to keep itself aloft, loitering on thermals as it scans the savanna for carrion, whilst the higher wing loadings of the albatross mean that it must cruise at much higher speeds to stay airborne.
This extra speed is important to the albatross as it allows it to hunt over great tracts of ocean for its widely scattered prey items. Wing loading is a very important factor in the flight performance of birds. In general it is found that animals with lower wing loadings tend to fly more slowly and are more maneuverable than do those with higher values. Wing loadings will also be affected by other phenomenon, such as the long legs stork and herons. These birds must land carefully to ensure that they do not damage their legs and so they need low wing loadings to allow them to come down very gently.
Compare this to the swan that requires a strip of water to land on, here the bird removes the remainder of its airspeed by sticking its feet out and ploughing through the water. The alula The faster a wing travels through the air the more air it passes through and so the more lift is produced. This is not a limitless relationship though because as the bird reaches higher velocities the drag induced by the wings increases too.
Secrets of flocking revealed
If the bird travels more slowly though, it passes through less air and thus it must gain more lift from that parcel of air. To do this it can either flap its wings to increase the airflow or it can increase the amount of air that it moves by increasing the angle of attack, thus forcing its wing through a greater volume of air. If the air passing over the wing starts to do so too slowly turbulence will be induced over the surface of the wing and it will start to stall.
Remember that for a wing to function correctly there has to be a smooth flow of air over the entire surface of the wing. If separation occurs and the air leaves the wing surface before it reaches the trailing edge a field of turbulence will be produced that will destroy the lift production of the wing.
To overcome this problem birds use a similar system to that used by aircraft. The second digit forms the alula, a small winglike structure that is drawn into the airflow of the wing, smoothing it and delaying the stall. This is a passive response to the change in airflow that can also be controlled by the bird, giving it greater control of flight parameters.
The aspect ratio of a wing and the overall wing shape will has profound consequences on the rate at which this phenomenon occurs. Narrow wings with less camber tend to have less dependence on the alula than short wings with heavy camber, so many passerines will have well developed alulas whilst the sea soarers will have less use for them. Moment of inertia During flapping flight, birds invest power to move the air aerodynamic power and to move the wings inertial power.
The moment of inertia value measured in kg m2 is important because, as with the aspect ratio of the wing, it gives us information on flight characteristics. This ensures that as little energy as possible is wasted on moving a heavy limb, it also means that the muscles can act on a lever mechanism, maximizing their power output. It is vitally important for a bird to keep the moment of inertia of its wing as low as possible and a close look at the wing highlights that adaptation.
The moment of inertia depends upon the distribution of mass along the wing, the more distal the mass, the higher its influence on inertia. Most of the, muscles, blood supply, tendons etc in the wing are fairly proximal and so have less influence on inertia. On the other hand, looking past the wrist it can be seen that the mass is made up predominantly of purely weight bearing material such as bone and feather.
At the same time as keeping the moment of inertia low, the wing must also maintain a reasonable resistance against bending or failure and so wing design must reflect a compromise between strength and weight.
Long wings will generally have a higher inertial value than shorter wings and so will be more difficult to flap. Gulls with their relatively long wings tend toward a lazy flight gait with a slow rate of flapping whilst sparrows and other small passerines, with their relatively short wings, are considerably more frenetic in their flight. Wing types Saville classified wings into 4 main types: Elliptical High aspect-ratio Slotted high-lift Elliptical wings tend to be found on birds adapted to forested, wooded and shrubby habitats where birds require good maneuverability and are generally short with a low aspect ratio.
These wings often have a high degree of slotting which is associated with the requirement of slow speed flight. Elliptical wings are found in the passerines, the gallinaceous species as well as woodpeckers and doves. High speed wings are possessed by birds that feed in the air or have to make long migratory hauls. They are seen in the swifts, swallows and also the falcons and some shorebirds.
These wings have a relatively high aspect ratio and are only slightly cambered, having an almost flat profile and are often swept back. The high aspect wing is found on soaring sea birds such as albatross and can also be seen on gliders. They, like the slotted high-lift wing can provide plenty of lift in the windswept environment in which they live. The slotted high-lift wing is a characteristic of many terrestrial soaring birds, such as the eagles and the vultures.