Bird flight

Bird flight is the primary mode of locomotion used by most bird species in which birds take off and fly. Flight assists birds with feeding, breeding, avoiding predators, and migrating.

Bird flight is one of the most complex forms of locomotion in the animal kingdom. Each facet of this type of motion, including hovering, taking off, and landing, involves many complex movements. As different bird species adapted over millions of years through evolution for specific environments, prey, predators, and other needs, they developed specializations in their wings, and acquired different forms of flight.

Various theories exist about how bird flight evolved, including flight from falling or gliding (the trees down hypothesis), from running or leaping (the ground up hypothesis), from wing-assisted incline running or from proavis (pouncing) behavior.

Domestic Pigeon Flock
A flock of domestic pigeons each in a different phase of its flap.

Basic mechanics of bird flight

Lift and drag

The fundamentals of bird flight are similar to those of aircraft, in which the aerodynamic forces sustaining flight are lift and drag. Lift force is produced by the action of air flow on the wing, which is an airfoil. The airfoil is shaped such that the air provides a net upward force on the wing, while the movement of air is directed downward. Additional net lift may come from airflow around the bird's body in some species, especially during intermittent flight while the wings are folded or semi-folded[1][2] (cf. lifting body).

Aerodynamic drag is the force opposite to the direction of motion, and hence the source of energy loss in flight. The drag force can be separated into two portions, lift-induced drag, which is the inherent cost of the wing producing lift (this energy ends up primarily in the wingtip vortices), and parasitic drag, including skin friction drag from the friction of air and body surfaces and form drag from the bird's frontal area. The streamlining of bird's body and wings reduces these forces.

Wings

Kea in Flight MC
A kea in flight.

The bird's forelimbs (the wings) are the key to flight. Each wing has a central vane to hit the wind, composed of three limb bones, the humerus, ulna and radius. The hand, or manus, which ancestrally was composed of five digits, is reduced to three digits (digit II, III and IV or I, II, III depending on the scheme followed[3]), which serves as an anchor for the primaries, one of two groups of flight feathers responsible for the wing's airfoil shape. The other set of flight feathers, behind the carpal joint on the ulna, are called the secondaries. The remaining feathers on the wing are known as coverts, of which there are three sets. The wing sometimes has vestigial claws. In most species these are lost by the time the bird is adult (such as the highly visible ones used for active climbing by hoatzin chicks), but claws are retained into adulthood by the secretarybird, screamers, finfoots, ostriches, several swifts and numerous others, as a local trait, in a few specimens.

Albatrosses have locking mechanisms in the wing joints that reduce the strain on the muscles during soaring flight.[4]

Even within a species wing morphology may differ. For example, adult European Turtle Doves have been found to have longer but more rounded wings than juveniles – suggesting that juvenile wing morphology facilitates their first migrations, with selection for flight maneuverability is more important after the juveniles’ first molt. [5]

Female birds exposed to predators during ovulation produce chicks that grow their wings faster than chicks produced by predator-free females. Their wings are also longer. Both adaptations may make them better at avoiding avian predators.[6]

Wing shape

FlightSilhouettes
Wing shapes

The shape of the wing is important in determining the flight capabilities of a bird. Different shapes correspond to different trade-offs between advantages such as speed, low energy use, and maneuverability. Two important parameters are the aspect ratio and wing loading. Aspect ratio is the ratio of wingspan to the mean of its chord (or the square of the wingspan divided by wing area). Wing loading is the ratio of weight to wing area.

Most kinds of bird wing can be grouped into four types, with some falling between two of these types. These types of wings are elliptical wings, high speed wings, high aspect ratio wings and soaring wings with slots.

Flugbild Sure 4
The budgerigar's wings, as seen on this pet female, allow it excellent manoeuvrability.

Elliptical wings

Technically, elliptical wings are those having elliptical (that is quarter ellipses) meeting conformally at the tips. The early model Supermarine Spitfire is an example. Some birds have vaguely elliptical wings, including the albatross wing of high aspect ratio. Although the term is convenient, it might be more precise to refer to curving taper with fairly small radius at the tips. Many small birds have having a low aspect ratio with elliptical character (when spread), allowing for tight maneuvering in confined spaces such as might be found in dense vegetation. As such they are common in forest raptors (such as Accipiter hawks), and many passerines, particularly non-migratory ones (migratory species have longer wings). They are also common in species that use a rapid take off to evade predators, such as pheasants and partridges.

High speed wings

High speed wings are short, pointed wings that when combined with a heavy wing loading and rapid wingbeats provide an energetically expensive, but high speed. This type of flight is used by the bird with the fastest wing speed, the peregrine falcon, as well as by most of the ducks. The same wing shape is used by the auks for a different purpose; auks use their wings to "fly" underwater.

The peregrine falcon has the highest recorded dive speed of 242 mph (389 km/h). The fastest straight, powered flight is the spine-tailed swift at 105 mph (170 km/h).

RoseateTern23
A roseate tern uses its low wing loading and high aspect ratio to achieve low speed flight.

High aspect ratio wings

High aspect ratio wings, which usually have low wing loading and are far longer than they are wide, are used for slower flight. This may take the form of almost hovering (as used by kestrels, terns and nightjars) or in soaring and gliding flight, particularly the dynamic soaring used by seabirds, which takes advantage of wind speed variation at different altitudes (wind shear) above ocean waves to provide lift. Low speed flight is also important for birds that plunge-dive for fish.

Soaring wings with deep slots

These wings are favored by larger species of inland birds, such as eagles, vultures, pelicans, and storks. The slots at the end of the wings, between the primaries, reduce the induced drag and wingtip vortices by "capturing" the energy in air flowing from the lower to upper wing surface at the tips,[7] whilst the shorter size of the wings aids in takeoff (high aspect ratio wings require a long taxi to get airborne).[7]

Flight

Birds use three types of flight. They are distinguished by wing motion.

Gliding flight

Lesser Flamingo
Lesser flamingos flying in formation.

When in gliding flight, the upward aerodynamic force is equal to the weight. In gliding flight, no propulsion is used; the energy to counteract the energy loss due to aerodynamic drag is either taken from the potential energy of the bird, resulting in a descending flight, or is replaced by rising air currents ("thermals"), referred to as soaring flight. For specialist soaring birds (obligate soarers), the decision to engage in flight are strongly related to atmospheric conditions that allow individuals to maximise flight-efficiency and minimise energetic costs.[8]

Flapping flight

When a bird flaps, as opposed to gliding, its wings continue to develop lift as before, but the lift is rotated forward to provide thrust, which counteracts drag and increases its speed, which has the effect of also increasing lift to counteract its weight, allowing it to maintain height or to climb. Flapping involves two stages: the down-stroke, which provides the majority of the thrust, and the up-stroke, which can also (depending on the bird's wings) provide some thrust. At each up-stroke the wing is slightly folded inwards to reduce the energetic cost of flapping-wing flight.[9] Birds change the angle of attack continuously within a flap, as well as with speed.[10]

Bounding flight

Small birds often fly long distances using a technique in which short bursts of flapping are alternated with intervals in which the wings are folded against the body. This is a flight pattern known as "bounding" or "flap-bounding" flight.[11] When the bird's wings are folded, its trajectory is primarily ballistic, with a small amount of body lift.[2] The flight pattern is believed to decrease the energy required by reducing the aerodynamic drag during the ballistic part of the trajectory,[12] and to increase the efficiency of muscle use.[13][14]

Hovering

Calypte anna, San Francisco
The ruby-throated hummingbird can beat its wings 52 times a second.

Several bird species use hovering, with one family specialized for hovering – the hummingbirds.[15][16] True hovering occurs by generating lift through flapping alone, rather than by passage through the air, requiring considerable energy expenditure.[15][17] This usually confines the ability to smaller birds, but some larger birds, such as a kite[18] or osprey[19][20] can hover for a short period of time. Although not a true hover, some birds remain in a fixed position relative to the ground or water by flying into a headwind. Hummingbirds,[16][17] kestrels, terns and hawks use this wind hovering.

Most birds that hover have high aspect ratio wings that are suited to low speed flying. Hummingbirds are a unique exception – the most accomplished hoverers of all birds.[15] Hummingbird flight is different from other bird flight in that the wing is extended throughout the whole stroke, which is a symmetrical figure of eight,[21] with the wing producing lift on both the up- and down-stroke.[16][17] Hummingbirds beat their wings at some 43 times per second,[22] while others may be as high as 80 times per second.[23]

Take-off and landing

Male Bufflehead taking off
A male bufflehead runs atop the water while taking off.
Magpie Goose taking off
A magpie-goose taking off.

Take-off is one of the most energetically demanding aspects of flight, as the bird must generate enough airflow across the wing to create lift. Small birds do this with a simple upward jump. That doesn't work for larger birds, which must take a run up to generate sufficient airflow. Large birds take off by facing into the wind, or, if they can, by perching on a branch or cliff so they can just drop off into the air.

Landing is also a problem for large birds with high wing loads. This problem is dealt with in some species by aiming for a point below the intended landing area (such as a nest on a cliff) then pulling up beforehand. If timed correctly, the airspeed once the target is reached is virtually nil. Landing on water is simpler, and the larger waterfowl species prefer to do so whenever possible, landing into wind and using their feet as skids. To lose height rapidly prior to landing, some large birds such as geese indulge in a rapid alternating series of sideslips or even briefly turning upside down in a maneuver termed as whiffling.

Coordinated formation flight

A wide variety of birds fly together in a symmetric V-shaped or a J-shaped coordinated formation, also referred to as an "echelon", especially during long distance flight or migration. It is often assumed that birds resort to this pattern of formation flying in order to save energy and improve the aerodynamic efficiency.[24][25] The birds flying at the tips and at the front would interchange positions in a timely cyclical fashion to spread flight fatigue equally among the flock members.

The wingtips of the leading bird in an echelon create a pair of opposite rotating line vortices. The vortices trailing a bird have an underwash part behind the bird, and at the same time they have an upwash on the outside, that hypothetically could aid the flight of a trailing bird. In a 1970 study the authors claimed that each bird in a V formation of 25 members can achieve a reduction of induced drag and as a result increase their range by 71%.[26]

Studies of waldrapp ibis show that birds spatially coordinate the phase of wing flapping and show wingtip path coherence when flying in V positions, thus enabling them to maximally utilise the available energy of upwash over the entire flap cycle. In contrast, birds flying in a stream immediately behind another do not have wingtip coherence in their flight pattern and their flapping is out of phase, as compared to birds flying in V patterns, so as to avoid the detrimental effects of the downwash due to the leading bird's flight.[27]

Adaptations for flight

Chicken wing
Diagram of the wing of a chicken, top view

The most obvious adaptation to flight is the wing, but because flight is so energetically demanding birds have evolved several other adaptations to improve efficiency when flying. Birds' bodies are streamlined to help overcome air-resistance. Also, the bird skeleton is hollow to reduce weight, and many unnecessary bones have been lost (such as the bony tail of the early bird Archaeopteryx), along with the toothed jaw of early birds, which has been replaced with a lightweight beak. The skeleton's breastbone has also adapted into a large keel, suitable for the attachment of large, powerful flight muscles. The vanes of each feather have hooklets called barbules that zip the vanes of individual feathers together, giving the feathers the strength needed to hold the airfoil (these are often lost in flightless birds). The barbules maintain the shape and function of the feather. Each feather has a major (greater) side and a minor (lesser) side, meaning that the shaft or rachis does not run down the center of the feather. Rather it runs longitudinally of center with the lesser or minor side to the front and the greater or major side to the rear of the feather. This feather anatomy, during flight and flapping of the wings, causes a rotation of the feather in its follicle. The rotation occurs in the up motion of the wing. The greater side points down, letting air slip through the wing. This essentially breaks the integrity of the wing, allowing for a much easier movement in the up direction. The integrity of the wing is reestablished in the down movement, which allows for part of the lift inherent in bird wings. This function is most important in taking off or achieving lift at very low or slow speeds where the bird is reaching up and grabbing air and pulling itself up. At high speeds the air foil function of the wing provides most of the lift needed to stay in flight.

The large amounts of energy required for flight have led to the evolution of a unidirectional pulmonary system to provide the large quantities of oxygen required for their high respiratory rates. This high metabolic rate produces large quantities of radicals in the cells that can damage DNA and lead to tumours. Birds, however, do not suffer from an otherwise expected shortened lifespan as their cells have evolved a more efficient antioxidant system than those found in other animals.

Evolution of bird flight

Most paleontologists agree that birds evolved from small theropod dinosaurs, but the origin of bird flight is one of the oldest and most hotly contested debates in paleontology.[28] The four main hypotheses are:

  • From the trees down, that birds' ancestors first glided down from trees and then acquired other modifications that enabled true powered flight.
  • From the ground up, that birds' ancestors were small, fast predatory dinosaurs in which feathers developed for other reasons and then evolved further to provide first lift and then true powered flight.
  • Wing-assisted incline running (WAIR), a version of "from the ground up" in which birds' wings originated from forelimb modifications that provided downforce, enabling the proto-birds to run up extremely steep slopes such as the trunks of trees.
  • Pouncing proavis, which posits that flight evolved by modification from arboreal ambush tactics.

There has also been debate about whether the earliest known bird, Archaeopteryx, could fly. It appears that Archaeopteryx had the brain structures and inner-ear balance sensors that birds use to control their flight.[29] Archaeopteryx also had a wing feather arrangement like that of modern birds and similarly asymmetrical flight feathers on its wings and tail. But Archaeopteryx lacked the shoulder mechanism by which modern birds' wings produce swift, powerful upstrokes; this may mean that it and other early birds were incapable of flapping flight and could only glide.[30] The presence of most fossils in marine sediments in habitats devoid of vegetation has led to the hypothesis that they may have used their wings as aids to run across the water surface in the manner of the basilisk lizards.[31][32]

In March 2018, scientists reported that Archaeopteryx was likely capable of flight, but in a manner substantially different from that of modern birds.[33][34]

From the trees down

Archaeopteryx lithographica (Berlin specimen)
It is unknown how well Archaeopteryx could fly, or if it could even fly at all.

This was the earliest hypothesis, encouraged by the examples of gliding vertebrates such as flying squirrels. It suggests that proto-birds like Archaeopteryx used their claws to clamber up trees and glided off from the tops.[35]

Some recent research undermines the "trees down" hypothesis by suggesting that the earliest birds and their immediate ancestors did not climb trees. Modern birds that forage in trees have much more curved toe-claws than those that forage on the ground. The toe-claws of Mesozoic birds and of closely related non-avian theropod dinosaurs are like those of modern ground-foraging birds.[36]

From the ground up

Feathers are very common in coelurosaurid dinosaurs (including the early tyrannosauroid Dilong).[37] Modern birds are classified as coelurosaurs by nearly all palaeontologists,[38] though not by a few ornithologists.[35][39] The original functions of feathers may have included thermal insulation and competitive displays. The most common version of the "from the ground up" hypothesis argues that bird's ancestors were small ground-running predators (rather like roadrunners) that used their forelimbs for balance while pursuing prey and that the forelimbs and feathers later evolved in ways that provided gliding and then powered flight.[40] Another "ground upwards" theory argues the evolution of flight was initially driven by competitive displays and fighting: displays required longer feathers and longer, stronger forelimbs; many modern birds use their wings as weapons, and downward blows have a similar action to that of flapping flight.[41] Many of the Archaeopteryx fossils come from marine sediments and it has been suggested that wings may have helped the birds run over water in the manner of the Jesus Christ lizard (common basilisk).[42]

Most recent attacks on the "from the ground up" hypothesis attempt to refute its assumption that birds are modified coelurosaurid dinosaurs. The strongest attacks are based on embryological analyses, which conclude that birds' wings are formed from digits 2, 3 and 4 (corresponding to the index, middle and ring fingers in humans; the first of a bird's 3 digits forms the alula, which they use to avoid stalling on low-speed flight, for example when landing); but the hands of coelurosaurs are formed by digits 1, 2 and 3 (thumb and first 2 fingers in humans).[43] However these embryological analyses were immediately challenged on the embryological grounds that the "hand" often develops differently in clades that have lost some digits in the course of their evolution, and therefore bird's hands do develop from digits 1, 2 and 3.[44][45][46]

Wing-assisted incline running

The wing-assisted incline running (WAIR) hypothesis was prompted by observation of young chukar chicks, and proposes that wings developed their aerodynamic functions as a result of the need to run quickly up very steep slopes such as tree trunks, for example to escape from predators. Note that in this scenario birds need downforce to give their feet increased grip.[47][48] But early birds, including Archaeopteryx, lacked the shoulder mechanism that modern birds' wings use to produce swift, powerful upstrokes. Since the downforce that WAIR requires is generated by upstrokes, it seems that early birds were incapable of WAIR.[30]

Pouncing proavis model

The proavis theory was first proposed by Garner, Taylor, and Thomas in 1999:

We propose that birds evolved from predators that specialized in ambush from elevated sites, using their raptorial hindlimbs in a leaping attack. Drag–based, and later lift-based, mechanisms evolved under selection for improved control of body position and locomotion during the aerial part of the attack. Selection for enhanced lift-based control led to improved lift coefficients, incidentally turning a pounce into a swoop as lift production increased. Selection for greater swooping range would finally lead to the origin of true flight.

The authors believed that this theory had four main virtues:

  • It predicts the observed sequence of character acquisition in avian evolution.
  • It predicts an Archaeopteryx-like animal, with a skeleton more or less identical to terrestrial theropods, with few adaptations to flapping, but very advanced aerodynamic asymmetrical feathers.
  • It explains that primitive pouncers (perhaps like Microraptor) could coexist with more advanced fliers (like Confuciusornis or Sapeornis) since they did not compete for flying niches.
  • It explains that the evolution of elongated rachis-bearing feathers began with simple forms that produced a benefit by increasing drag. Later, more refined feather shapes could begin to also provide lift.

Uses and loss of flight in modern birds

Birds use flight to obtain prey on the wing, for foraging, to commute to feeding grounds, and to migrate between the seasons. It is also used by some species to display during the breeding season and to reach safe isolated places for nesting.

Flight is more energetically expensive in larger birds, and many of the largest species fly by soaring and gliding (without flapping their wings) as much as possible. Many physiological adaptations have evolved that make flight more efficient.

Birds that settle on isolated oceanic islands that lack ground-based predators often lose the ability to fly. This illustrates both flight's importance in avoiding predators and its extreme demand for energy.

See also

Notes

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References

  • Alexander, David E. Nature's Flyers: Birds, Insects, and the Biomechanics of Flight. 2002(hardcover) and 2004(paperback). Baltimore: The Johns Hopkins University Press. ISBN 0-8018-6756-8(hardcover) and 0801880599(paperback).
  • Brooke, Michael and Tim Birkhead (editors). The Cambridge Encyclopedia of Ornithology. 1991. Cambridge: Cambridge University Press. ISBN 0-521-36205-9.
  • Burton, Robert. Bird Flight. Facts on File, 1990
  • Campbell, Bruce, and Elizabeth Lack (editors). A Dictionary of Birds. 1985. Calton: T&A D Poyse. ISBN 0-85661-039-9.
  • Cornell Laboratory of Ornithology handbook of bird biology. 2004. Princeton University Press. ISBN 0-938027-62-X. (hardcover)
  • Del Hoyo, Josep, et al. Handbook of Birds of the World Vol 1. 1992. Barcelona: Lynx Edicions, ISBN 84-87334-10-5.
  • Wilson, Barry (editor). Readings from Scientific American, Birds. 1980. San Francisco: WH Freeman. ISBN 0-7167-1206-7.
  • Attenborough, D.1998. The Life of Birds. Chapter 2. BBC Books. ISBN 0563-38792-0.

External links

Bird migration

Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting by humans, and is driven primarily by availability of food. It occurs mainly in the northern hemisphere, where birds are funneled on to specific routes by natural barriers such as the Mediterranean Sea or the Caribbean Sea.

Migration of species such as storks, turtle doves, and swallows was recorded as many as 3,000 years ago by Ancient Greek authors, including Homer and Aristotle, and in the Book of Job. More recently, Johannes Leche began recording dates of arrivals of spring migrants in Finland in 1749, and modern scientific studies have used techniques including bird ringing and satellite tracking to trace migrants. Threats to migratory birds have grown with habitat destruction especially of stopover and wintering sites, as well as structures such as power lines and wind farms.

The Arctic tern holds the long-distance migration record for birds, travelling between Arctic breeding grounds and the Antarctic each year. Some species of tubenoses (Procellariiformes) such as albatrosses circle the earth, flying over the southern oceans, while others such as Manx shearwaters migrate 14,000 km (8,700 mi) between their northern breeding grounds and the southern ocean. Shorter migrations are common, including altitudinal migrations on mountains such as the Andes and Himalayas.

The timing of migration seems to be controlled primarily by changes in day length. Migrating birds navigate using celestial cues from the sun and stars, the earth's magnetic field, and mental maps.

Codex on the Flight of Birds

Codex on the Flight of Birds is a relatively short codex from c. 1505 by Leonardo da Vinci. It comprises 18 folios and measures 21 × 15 centimetres. Now held at the Biblioteca Reale in Turin, Italy, the codex begins with an examination of the flight behavior of birds and proposes mechanisms for flight by machines. Leonardo constructed a number of these machines, and attempted to launch them from a hill near Florence. However, his efforts failed.In the codex, Leonardo notes for the first time that the center of gravity of a flying bird does not coincide with its center of pressure.

Coracoid

A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (which is to say marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is not homologous with the coracoid bone of most other animals.In other tetrapods it joins the scapula to the front end of the sternum and has a notch on the dorsal surface which, along with a similar notch on the ventral surface of the scapula, forms the socket in which the proximal end of the humerus (upper arm bone) is located. The acrocoracoid process is an expansion adjacent to this contact surface, to which the shoulderward end of the biceps brachii muscle attaches in these animals. In birds (and generally theropods and related animals), the entire unit is rigid and called scapulocoracoid. This plays a major role in bird flight. In dinosaurs the main bones of the pectoral girdle were the scapula (shoulder blade) and the coracoid, both of which directly articulated with the clavicle.In fish it provides the base for the pectoral fin.Monotremes, as well as the extinct therapsids, possess both the coracoid bone of reptiles (here referred to as the procoracoid, or anterior coracoid), and the coracoid process of other mammals, with the latter being present as a separate bone.

Farrar LSG-1 Bird Flight Machine

The Farrar LSG-1 Bird Flight Machine is an American, high-wing, V-tailed, single-seat, experimental research glider that was designed and built by Demetrius F. Farrar Jr. in 1969 for exploring aspects of bird flight.

Flight feather

Flight feathers (Pennae volatus) are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tail are called rectrices (), singular rectrix (). The primary function of the flight feathers is to aid in the generation of both thrust and lift, thereby enabling flight. The flight feathers of some birds have evolved to perform additional functions, generally associated with territorial displays, courtship rituals or feeding methods. In some species, these feathers have developed into long showy plumes used in visual courtship displays, while in others they create a sound during display flights. Tiny serrations on the leading edge of their remiges help owls to fly silently (and therefore hunt more successfully), while the extra-stiff rectrices of woodpeckers help them to brace against tree trunks as they hammer on them. Even flightless birds still retain flight feathers, though sometimes in radically modified forms.

The moult of their flight feathers can cause serious problems for birds, as it can impair their ability to fly. Different species have evolved different strategies for coping with this, ranging from dropping all their flight feathers at once (and thus becoming flightless for some relatively short period of time) to extending the moult over a period of several years.

List of birds by flight heights

Migratory birds and birds of prey can reach substantial heights while flying. This list gives the highest recorded flights for various species (limited to observations of 4,500 metres/15,000 feet and above).

List of birds by flight speed

This is a list of the fastest flying birds in the world. A bird's velocity is necessarily variable; a hunting bird will reach much greater speeds while diving to catch prey than when gliding. The bird with the greatest airspeed velocity is the Peregrine falcon, able to exceed 321.8 km/h (200 mph) in its hunting dives. The greatest self-powered horizontal speed is achieved by Homing Racing Pigeons. They can fly 1100 km (700 miles) in a single day, and they have been recorded flying at 177 km/h (110 miles per hour), making them the birds with the fastest speed ever recorded on a self-powered flight, and the fastest endurance flight.

List of soaring birds

This is a list of soaring birds, which are birds that can maintain flight without wing flapping, using rising air currents. Many gliding birds are able to "lock" their extended wings by means of a specialized tendon.

Bird of preyBuzzards

Condors

Eagles

Falcons

Harriers

Hawks

Kites

Osprey

Secretary bird

VulturesPasserineChoughs

Raven

WoodswallowsCranesSandhillHeronsStorksSea birdsAlbatrosses

Frigatebirds

Gulls

Pelicans

Petrels

Shearwaters

TernsExtinctArgentavis

Lübeck–Puttgarden railway

The Lübeck–Puttgarden railway is part of the international Vogelfluglinie (Bird Flight Line) between Germany and Denmark and connects Lübeck with Puttgarden on the Baltic Sea island of Fehmarn in the German state of Schleswig-Holstein.

Organisms at high altitude

Organisms can live at high altitude, either on land, in water, or while flying. Decreased oxygen availability and decreased temperature make life at such altitudes challenging, though many species have been successfully adapted via considerable physiological changes. As opposed to short-term acclimatisation (immediate physiological response to changing environment), high-altitude adaptation means irreversible, evolved physiological responses to high-altitude environments, associated with heritable behavioural and genetic changes. Among animals, only few mammals (such as yak, ibex, Tibetan gazelle, vicunas, llamas, mountain goats, etc.) and certain birds are known to have completely adapted to high-altitude environments.Human populations such as some Tibetans, South Americans and Ethiopians live in the otherwise uninhabitable high mountains of the Himalayas, Andes and Ethiopian Highlands respectively. The adaptation of humans to high altitude is an example of natural selection in action.High-altitude adaptations provide examples of convergent evolution, with adaptations occurring simultaneously on three continents. Tibetan humans and Tibetan domestic dogs share a genetic mutation in EPAS1, but it has not been seen in Andean humans.

Origin of avian flight

"Evolution of flight" redirects here. See also flying and gliding animals and insect flight.Around 350 BCE, Aristotle and other philosophers of the time attempted to explain the aerodynamics of avian flight. Even after the discovery of the ancestral bird Archaeopteryx over 150 years ago, debates still persist regarding the evolution of flight. There are three leading hypotheses pertaining to avian flight: Pouncing Proavis model, Cursorial model, and Arboreal model. Archaeopteryx, the oldest known ancestor of modern birds, could provide clues to the origin of avian flight.

In March 2018, scientists reported that Archaeopteryx was likely capable of flight, but in a manner substantially different from that of modern birds.

Origin of birds

The scientific question of within which larger group of animals birds evolved, has traditionally been called the origin of birds. The present scientific consensus is that birds are a group of theropod dinosaurs that originated during the Mesozoic Era.

A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany. Birds and extinct non-avian dinosaurs share many unique skeletal traits. Moreover, fossils of more than thirty species of non-avian dinosaur have been collected with preserved feathers. There are even very small dinosaurs, such as Microraptor and Anchiornis, which have long, vaned, arm and leg feathers forming wings. The Jurassic basal avialan Pedopenna also shows these long foot feathers. Paleontologist Lawrence Witmer concluded in 2009 that this evidence is sufficient to demonstrate that avian evolution went through a four-winged stage. Fossil evidence also demonstrates that birds and dinosaurs shared features such as hollow, pneumatized bones, gastroliths in the digestive system, nest-building and brooding behaviors.

Although the origin of birds has historically been a contentious topic within evolutionary biology, only a few scientists still debate the dinosaurian origin of birds, suggesting descent from other types of archosaurian reptiles. Within the consensus that supports dinosaurian ancestry, the exact sequence of evolutionary events that gave rise to the early birds within maniraptoran theropods is disputed. The origin of bird flight is a separate but related question for which there are also several proposed answers.

Parrot harness

A parrot harness or bird flight harness is a type of pet harness that is specifically designed to be worn by a parrot. A parrot harness may enable a companion parrot to be taken outdoors without flying away if attempted, as they cannot by being restrained. Some parrots may dislike wearing a harness and bite at it, but parrots that are harness-trained from a very young age may accept them willingly; more often, though, parrots must be very carefully and gradually accustomed and trained to wear a harness. Care must be taken that the parrot does not feel threatened. Properly trained parrots often appear to enjoy wearing their harnesses if they associate them with going outdoors.

It can even be given some limited flight outside. However, this can be potentially dangerous for the parrot, which may be initially frightened by unfamiliar events, noises, and objects. It is usually best to first take the parrot out in a cage or carrier to let it become accustomed to being outdoors. Parrot harnesses are available commercially in a range of brands and sizes, fitting small birds such as budgerigars and cockatiels, all the way up to the largest macaws and cockatoos. Some parrot owners may choose to make their own harnesses.

Heavy harnesses that require assembly with metal buckles and clips can be uncomfortable. They may be broken or unlatched by some larger birds with strong beaks. A leash should always be fastened securely to the person holding the leash (such as by an elastic band around the wrist) to avoid the possibility of dropping the leash, as a dropped leash may become entangled in a tree or other object if a parrot flies off. A harness should only be used when the parrot is supervised and should never be used to tether a parrot to a perch or other object.

The best way to train a parrot to wear a harness is to use positive and negative reinforcement. Negative reinforcement is used to reward the parrot until it overcomes its fear of the harness. Food treats are used as positive reinforcement to reward the parrot for putting on the harness. A well trained parrot will put the harness on itself by slipping its head through the collar.

Phil Schaap

Phil Schaap (born April 6, 1951) is an American jazz disc jockey, historian, archivist and producer. He has hosted jazz shows on the Columbia University WKCR since 1970; he currently hosts two, Bird Flight and Traditions In Swing, both since 1981.

Puttgarden station

Puttgarden station is a major ferry terminal on the Vogelfluglinie (bird flight line) on the island of Fehmarn in the German state of Schleswig-Holstein. It lies between the town of Puttgarden and Marienleuchte.

It primarily serves the needs of international long distance traffic, but since the reintroduction of regional traffic on the line it is again of regional importance for Fehmarn.

V formation

A V formation is the symmetric V-shaped flight formation of flights of geese, ducks, and other migratory birds. V formations also improve the fuel efficiency of aircraft and are used on military flight missions.

Vogelfluglinie

The Vogelfluglinie (German) or Fugleflugtslinjen (Danish) is a transport corridor between Copenhagen, Denmark, and Hamburg, Germany.

As the Danish and German names (literally: bird flight line) imply, the corridor is also an important bird migration route between arctic Scandinavia and Central Europe.

Whiffling

Whiffling is a term used in ornithology to describe the behavior whereby a bird rapidily descends with a zig-zagging, side-slipping motion. Sometimes to whiffle, a bird flies briefly with its body turned upside down but with its neck and head twisted 180 degrees around in a normal position. The aerodynamics which usually give a bird lift during flying are thereby inverted and the bird briefly plummets toward the ground before this is quickly reversed and the bird adopts a normal flying orientation. This erratic motion resembles a falling leaf, and is used to avoid avian predators or may be used by geese (family Anatidae) to avoid a long, slow descent over an area where wildfowling is practised.The behavior is seen in several species including lesser yellowlegs (Tringa flavipes), the black-tailed godwit (Limosa limosa), the northern lapwing (Vanellus vanellus), geese (e.g. pink-footed goose (Anser brachyrhynchus)), three species of scoter (Melanitta), and other members of the family Anatidae.

Wing

A wing is a type of fin that produces lift, while moving through air or some other fluid. As such, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expressed as its lift-to-drag ratio. The lift a wing generates at a given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a significantly smaller thrust to propel the wings through the air at sufficient lift.

Lifting structures used in water, include various foils, including hydrofoils. Hydrodynamics is the governing science, rather than aerodynamics. Applications of underwater foils occur in hydroplanes, sailboats and submarines.

Birds (class: Aves)
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