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How Do Birds Fly?

Updated on June 6, 2014

Taking Flight

A magpie goose taking to the air showing its outstretched primary feathers.
A magpie goose taking to the air showing its outstretched primary feathers. | Source

Freedom Of The Air

Freedom of the air enables these flamingos' to choose the best places for feeding and roosting. With advantages like this, birds as a class have evolved twice as many species as mammals.
Freedom of the air enables these flamingos' to choose the best places for feeding and roosting. With advantages like this, birds as a class have evolved twice as many species as mammals. | Source

The Mastery Of Flight by Sir David Attenborough

How Flight Works

If numbers of species are a worthwhile guide, birds-with over 8000 species that fly compared with 4000 non-flying mammal species are arguably the most successful class of vertebrates today. Their success is due in large part to the powers of movement, and thus the wide choice of habitat, that flight allows.

The mechanical problem concerned with flight is how to lift a weight clear of the ground, keep it airborne for a practical time and propel it forwards at the same time. For this, an upward force (lift) and a forward force (propulsion) are required.

A glance at the wing cross-section of a model aircraft shows the solution to this problem. Rounded and thicker at the front than at the slender ‘trailing edge,’ shallowly convex above and concave below, this is called an aerofoil section. Move an aerofoil section forwards through the air and it causes air to flow in such a way across its surfaces as to produce lift. The discovery of the aerofoil section enabled man to fly: birds of course have used it for eons. The inner portion of a bird’s wing, which is anatomically equivalent to the human forearm, has a classic aerofoil section.

The next requirement is propulsion. For this, birds rely on the beating of their wings, powered by the breast muscles (the pectorals) which are highly developed. Propulsion is provided by the outer part of the wing, from the angle (where the front edge bends) to the tip. This part is anatomically equivalent to the human hand, from wrist to fingertips. The ten or twelve long, strong feathers at the end of the wing (the flight feathers) are vitally important and merit their technical name ‘primaries.’

How An Aerofoil Works

A diagram showing how a bird generates lift. The lift itself is created by pressures from the air flow over the top of the wing.
A diagram showing how a bird generates lift. The lift itself is created by pressures from the air flow over the top of the wing. | Source

Nature's Fighter Jet- The Peregrine Falcon

Variable Geometry

The vast majority of aircraft have wings and tail securely fixed in position, and only the provision of flaps and ailerons allows their shape to be altered so that the aircraft is manoeuvrable. Some of the most sophisticated modern fighter planes are famed for their ‘variable geometry’ but this merely allows the wings to swing in and out from the fuselage. It’s easy to see, therefore, how much more manoeuvrable birds are than aircraft, with an almost infinite variety of positions, not just of the wings and tail, but of the parts of the wings and often of the individual feathers.

A Running Start

A bird like this male bufflehead duck need to literally run across the water to generate the lift needed to take off, as it is almost impossible to complete a conventional takeoff on open water.
A bird like this male bufflehead duck need to literally run across the water to generate the lift needed to take off, as it is almost impossible to complete a conventional takeoff on open water. | Source

Taking Off And Landing

To complete their manoeuvrability, birds have to be able to take off and land at will. Many survive precisely because they can do this at a split second’s notice, escaping the ever present danger of attacking predators. Taking off requires the maximum output of propelling force (thrust) that the bird is capable of producing.

The smaller species are capable of exerting sufficient effort to lift themselves off the ground with no preliminary ‘run.’ Heavier birds, on the other hand, have to survive without the ability to respond to danger by an instant take off. Large water birds, such as swans, attain safety by spending much of their time on the open water, far away from the predators on dry land. Their take off is so difficult that they often have to ‘run’ some distance across the water surface, and can only occupy stretches of water large enough to allow space for this long take off.

To land, birds need to ‘spill’ the lift that their wings and tails have been providing during flight. One way to lose lift is to raise the tail, thus steering into a descent towards the landing place. To halt their flight, birds rear up in mid-air to an upright posture as they approach the selected spot. This tilts the wings until they are nearly in a vertical plane, so that they can act as ‘brakes,’ or even beat against the direction of flight. The tail is lowered, also acting as a brake against forward movement.

The hard impact of landing is absorbed by flexible legs and strong muscles, which are attached to the most rigid part of the bird’s skeleton- the pelvis, which is fused on to the lower spine for added strength.

Types Of Bird Flight

  1. High manoeuvrability: The wren can fly neatly among dense undergrowth. While the partridge is an expert at the sudden escape flight.
  2. General purpose: Robins, finches and geese are among the many 'all-rounders.'
  3. High performance: Long, narrow primaries give the swift and the hobby (a species of falcon) maximum power with the least air resistance.
  4. Gliding:The gannet and the Manx shearwater have narrow wings with a long lift section for sea gliding.
  5. Soaring: The wings of the raven and the buzzard are broad with a long lift section, useful for catching upward air currents.

In Perfect Formation

Canada geese have a 'general purpose' wing layout, but improve their flight efficiency by means of a cunning use of the V pattern. The bird at the front creates turbulence in its wake with the beating of its wings; giving lift to the other birds.
Canada geese have a 'general purpose' wing layout, but improve their flight efficiency by means of a cunning use of the V pattern. The bird at the front creates turbulence in its wake with the beating of its wings; giving lift to the other birds. | Source

Shapes Of Wings

In the course of evolution, families of birds have developed the capability of flight in a number of different ways to suit the various modes of life they have adopted.

First, there are naturally many birds without a specialised form of flight and these have a ‘general purpose’ wing layout. In this layout, the lift and power sections of the wing are roughly of equal length. The wing is twice as long as it is wide. Garden birds such as the greenfinch and the robin fit into this category. So, too, do larger birds like geese.

If the ‘general purpose’ category is placed in the middle of a range of flight styles, one of the extremes on the scale would be ‘high manoeuvrability.’ Birds in this category have wings with lift and power sections of equal length, but the wing is much rounder in appearance, rather than long, for it is almost as broad at its base as it is long from base to tip. Examples include game birds, which need fast and almost vertical take-off to escape predators, and birds of thick cover such as the tiny wren. The wing pattern provides strong propulsion, but the high manoeuvrability results from the broad wing area.

The other extreme consists of the birds that specialise in extra-efficient flight. Among these species, flight is developed to the highest standards of performance. For maximum speed, their wings do not have the same proportions as those of the other categories of birds. The power section of the wing (the primary feathers) is much longer than the lift section- in some cases by as much as a factor of four- and the wing is long and thin. The swift is a prime example of this.

A Perfect Glider

The black primaries of the gannet clearly show the proportions of the wing layout: the white lift section is longer, a good gliding characteristic.
The black primaries of the gannet clearly show the proportions of the wing layout: the white lift section is longer, a good gliding characteristic. | Source

Fly Like An Eagle

A golden eagle soars effortlessly. The primary feathers are spread out to obtain maximum advantage from rising air currents; they are also specially shaped to reduce turbulence, helping the eagle to gain speed when gliding downwards.
A golden eagle soars effortlessly. The primary feathers are spread out to obtain maximum advantage from rising air currents; they are also specially shaped to reduce turbulence, helping the eagle to gain speed when gliding downwards. | Source

Ways Of Gliding

Gliding (in the case of birds) is flying without flapping wings. Two groups of birds are adapted for this type of flight: those that use wind power to travel over the sea (gliding in the common sense of the word) and those that not only glide but also exploit rising air currents to gain height (soaring).

The ‘gliding’ birds have extremely long and narrow wings, with a lift section either as long as the power section or longer. Most of them are oceanic birds, best exemplified by the albatrosses of the southern hemisphere but represented in British waters by the fulmar, the gannet, and the Manx shearwater.

The ‘soaring’ birds use up-currents at a ridge of hills or, in warm conditions, columns of rising air called thermals. In warmer countries these currents are the province of the vultures, but in Britain and Ireland the best examples of soaring flight are given by the raven, the buzzard and the golden eagle.

These birds are quite different in silhouette from the seagoing gliders: they too have a lift section as long as the power section or else even longer, but their wings are much broader. Further, the wingtips, rather than being pointed, have a broadly splayed ‘fingered’ appearance which helps to reduce turbulence. The birds flap slowly and laboriously into the air in wide circles, but once they catch the rising air they soar effortlessly.

© 2013 James Kenny

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    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Thank you very much Chris- always appreciated!

    • christopheranton profile image

      Christopher Antony Meade 4 years ago from Gillingham Kent. United Kingdom

      Some poet said "Oh for the wings of a dove", but I think the wings of a Golden Eagle would be better. Thanks James for another of your great natural history articles.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Wow I didn't know about certain flying birds having solid bones, because even flightless birds have hollow bones, demonstrating that they evolved from an ancestor that flew. Thanks very much for that.

    • The Examiner-1 profile image

      The Examiner-1 4 years ago

      JKenny - Interesting article. Did you know that there are also a small percentage of birds which take longer to take off because their bones are solid, instead of hollow like most of the birds.

      The reason that birds make all of that noise when they fly is to avoid aerial collisions while in large groups.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Thank you very much Eddy. You have a great day too.

    • Eiddwen profile image

      Eiddwen 4 years ago from Wales

      So very interesting indeed and have a great day Kenny. Voted up and shared.

      Eddy..

    • JKenny profile image
      Author

      James Kenny 4 years ago from Birmingham, England

      Oh yes I agree. I often see Canada geese flying in the same V formation, and as well as making a racket with their wings, they constantly honk at each other.

    • HollieT profile image

      HollieT 4 years ago from Manchester, United Kingdom

      I actually read about this on this very site. I suppose, however, man has been trying to replicate the flight of birds for sometime, we studied them and learnt to fly. Shame that the occasional idiot believes that they can help us cut our petrol bills too.

      As a Brit, I mostly notice the V formation when ducks migrate (because they're quite noisy with it) And pretty amazing to boot!

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Oh, so that's why people tailgate, and there's me thinking they were just being arrogant so and so's hehe! Of course, in the natural world, the reasoning is much more solid. Thanks for popping by.

    • HollieT profile image

      HollieT 4 years ago from Manchester, United Kingdom

      The V formation has always fascinated me, the extra efficiency makes perfect sense. But also reminds me of those misguided people who believe that if you tailgate the car in front of you, it's possible to save petrol! Don't ask me why they've reached this conclusion! I know birds would never be that stupid. :)