How do vultures fly so high and survive?

Cape Vulture - Vulture Restaurant @ VulPro - Photo Copyright Mandy Schrode
Cape Vulture – Vulture Restaurant @ VulPro – Photo Copyright Mandy Schroder

Vultures are amazing birds that can soar and glide for great distances, they have adapted over time to allow them to fly at great altitudes where oxygen is in short supply.

Mechanics of flight

Whether you are flying in an airplane or a vulture gliding across the sky, flying remains a balance between two sets of forces – “lift and weight” and “thrust and drag”. Lift is created by the flow of air over the wings and weight is created as a result of gravity.  Vulture’s wings are concave on their underside and convex on the upper surface, because of this shape the air that travels over the wing has a greater distance to travel resulting in it speeding up, this causes the pressure to drop (this is because the same amount of air is exerting its pressure over a larger area above the wing than below it.  This creates “lift” or sucks the wing up.

At the same time the exact opposite is happening on the underside of the wing, the air slows down, creates more pressure and “pushes” the wing up. This push and pull effect happens the most along the thin trailing (back) edge of the wing and causes a spiralling vortex (whirling mass) of air disturbance at the wing tip which increases the drag.

Gliding & Soaring

Vultures are masters at soaring and gliding, hanging in the air without having to flap their wings.   Their wings are large, ideal for gliding, but very hard work to flap for flight.  Soaring means that vultures don’t lose height and often climb higher in altitude by using no energy of their own – instead using the thermals (rising masses of warm air), obstruction currents which are produced when wind currents hit mountains or tall buildings cause the air to rise lifting vultures to higher altitudes.  Vultures have large, broad wings and their proportion of bodyweight to wing size is low, making them the perfect gliders and soarers.

Brain straining fact:

 “Aerodynamic properties are measured by aspect ratio, which is the ratio of wing length divided by wing breadth. Long wings are better for gliding but harder to flap quickly and are therefore not much good at quick acceleration.  Wing loading is the relationship between total body-mass measured in grams versus total wing area measured in square centimetres.” (http://www.iaszoology.com/flight-adaptations/)

Feathers for Temperatures

Cape Vulture - back feathers up close
Cape Vulture – back feathers up close

At the higher altitudes, temperatures can drop to -60°C, to survive this high fliers have developed a layer of soft down feathers that act as insulation – exactly why we use down duvets in winter.  Special feathers called “Contour feathers” cover the body, streamlining it and effectively reduce the drag.  “Remiges” are primary feathers, found on the wings they help with flight and provide wing shape.  “Rectrices” are tail feathers which stretch sideways making the tail work like a rudder for turning and balancing.

Bullet shaped bodies

The vulture’s body shape is suited to flight with the centre of gravity being situated slightly below and behind the wings, the placement of the centre of gravity helps with better balance in flight.  Added to the position of the centre of gravity a large number of the organs and large muscles are found near the centre of gravity.

Wings       

A vulture’s wings are the equivalent of our forelimbs or arms, they attach to the body closer to the vulture’s centre of gravity.  The “hand” bones are small, fused, flattened and are specially adapted to manipulate the flight feathers and “feel” the air for riding thermals.

Bare Bones

Pneumatization means “The development of air cells or cavities, such as those of the mastoid and ethmoidal bones.” (www.dictionary.com/browse/pneumatization)

Evolution has allowed vultures to adapt for flying by reducing their weight by:

  • Fusion of some bones
  • Removal of unnecessary ones
  • Pneumatisation of bones
  • Large bones are often connected to respiratory system air sacs.

To ensure that their bones remain strong they have internal truss like reinforcing.  Fusion of certain bones lightens the skeleton while increasing its strength.   An important adaptation is the fusion of the caudal (tail) bones into what is called a pygostyle(the Pope’s Nose on a chicken).  This pygostyle supports the tail feathers, with the tail working as a rudder it needs to remain strong.

Vultures also have no teeth, having evolved with a beak which is lighter.  Bird’s ribs are stronger than ours as they have hooked boney extensions (uncinate processes) which overlap with the rib behind them providing extra strength and stability.

A vulture’s skull is made up thin hollow bones making it very light

Height Records

  • Andean Condor 15 000feet
  • White Stork 16 000 feet
  • Bar-tailed Godwit – 20000 feet
  • Mallard – 21000 feet
  • Bearded Vulture – 24000 feet
  • Alpine Chough – 26500 feet
  • Whooper Swan – 27000 feet
  • Bar-headed Goose – 29000 feet
  • Common Crane – 33000 feet
  • Ruppell’s Griffon Vulture – 37000 feet [11,274 m when a Ruppell’s griffo collided into a commercial airline over western Africa (Martin, 1987)]

ANATOMICAL ADAPTATIONS

Respiratory System

High Flyers counteract the reduced oxygen levels by having an amazing lung respiratory system, which uses the smallest amount of oxygen available to its full effect.  So why do vultures fly so high… to use the natural jet streams found at higher altitudes, allowing them to cover massive distances with little effort.

A vulture’s respiratory system is proportionately larger than ours is.  Their lungs are smaller and less flexible than ours are as well as being connected with a network of large thin walled air sacs in the body.  The air sacs are also interconnected with the air spaces in the bones.  Vultures like most birds have a unidirectional method of breathing, this means that fully oxygenated air is always entering the lungs unlike us where we breathe into and out of our lungs, resulting in fresh air mixing with old air.

Respiration-bird-mammal-insectAnimated gif used with permission of and created by Eleanor Lutz (Eleanor’s website: http://tabletopwhale.com/2014/10/24/3-different-ways-to-breathe.html)

Heart & Blood

A vulture’s heart is large and powerful as well as being similar to ours by having 4 chambers.  The Bird’s heart is large, powerful, four-chambered and of the same basic design as that of a mammal. The vulture’s circulatory system is like its respiratory system in that the blood is separated into oxygenated and de-oxygenated, making them well equipped to handle their high flying.  They also have higher blood pressure and blood glucose levels than ours.

Metabolism

Birds have high metabolism and are able to generate and regulate their body temperature (endothermy) for rapid availability of power and maintenance of high body temp at cold altitudes.

References:
Sabi Sabi Wild Facts: Vultures
http://www.iaszoology.com/flight-adaptations/ http://themysteriousworld.com/10-highest-flying-birds-in-the-world/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3140315/ http://jeb.biologists.org/content/214/15/2455 http://www.mnn.com/earth-matters/animals/photos/9-birds-that-set-records-for-their-amazing-flights/highest-flier http://blogs.bu.edu/bioaerial2012/2012/09/26/the-ruppells-griffon-vulture-the-highest-recorded-flying-bird/
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