Bird flight

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  • Bird Flight
    • Physics of flight
      • Aerofoil
        • Forward thrust, backward drag, upward lift, downward weight
        • Can assume shape, but some more membranous as in bats and flying fish
      • Retaining control
        • Low speed, need steeper angle = turbulence on upper wing surface that reduces lift
        • Deploying alula restores laminar air flow over the wing and minimises turbulence and increase lift
        • Tail
          • Act as rudder (steer); air brake
          • larger=  improves manoeuvrability; smalll reduces ability for sharp turns
      • Weight-reducing Adaptations
        • Thin, hollow bones; extremely light feathers; skin gland /teeth/heavyjaw/tail verts elimination....bone fusion in pectoral and pelvic girdles and vert columb
        • Branching air sacs, oviparity, atrophy of gonads
      • Power-increasing adaptations
        • Endothermy; heat conservation plumage; energy-rich diet; rapid and efficient digestion; high blood glucose; four-chambered heart and double circulation; high pressure circulation; efficient respiratory; breathing movements synchronised with wing movements; high metabolism
    • Types of wings
      • Elliptical wings
        • Short, road, low aspect ratio
        • Turbulence created by broad tip of wing offset by slotting primary feathers that creates lift
        • Traded aerodynamic advantages of longer wing for manoeuvrability of a shorter one
        • Less lift but reduced wing loading
        • Flight speeds are relatively low
        • E.g. sparrow, blackbird, grouse, thrush, crow
      • High-speed wings
        • Tapered, pointed and often swept back
        • Primary feathers have little slotting
        • High aspect ratio but energetic expensive- flapping is necessary to generate lift
        • Flight is high speed and control is crucial
        • e.g. swift, falcon, duck, sandpiper, tern
      • Slotted high-lift wing
        • E.g. eagle, buteo, stork
        • Soaring
        • Broad wing with deep camber and prominent primary slotting- broadness catch rising air
        • Moderate aspect ratio
        • Slow flight speed
      • High-aspect ratio wings
        • e.g. albatross, gannet and gull
        • Soaring
        • Long, thin wings but proximal wing is elongated so provides large area to generate a lot of lift
        • Efficient at relatively high air speeds
        • Untitled
    • Structure of wings
      • Pterosaur
        • Extended IV digit and skin flap
      • Bat
        • Extended digits except first (thumb)
        • Wings more broad than pterosaurs
      • Bird
        • Reduced digits and feathers
        • each feather is an aerofoil
          • Modified keratinised scales
          • Primary and secondary feathers/covers. Alula and marginal covert feathers.
        • great control over aerofoil
    • Types of flight
      • Powered flight
        • Less pressure pushing down.... lifts up!
        • Shape of aerofoil changes
        • Use own musculature
          • Most use this, not all but especially for take off (may employ other strategies for staying in the air
          • Keel is attached to sternum- sight of muscle attachment
          • Contraction, humorous goes down
          • Hand-wing: bowing allows for musculature (increases control)
          • Expensive, so flightlessness favoured,
        • Downstroke: primaries/secondaries stiffen, form a link on this downstroke that little wind can get through
          • Pushes wrist and wing forward to provide thrust and lift
          • Wing moving faster than the bird forcing the air upwards towards the rear of the bird
          • Primary feathers twist, to reduce angle of attack and minimise risk of stalling (otherwise too much resistance to air flow and bird could stall)
        • Upstroke: wings twist, feathers part which allows wind between them
          • Allow no wasted energy to move up
          • Pulls wrist and wing backwards and upwards
        • Figure eight
      • Wing loading
        • ratio of body weight to wing area
          • Smaller birds: lighter wind loadings than larger birds
            • Wing loading imposes the ultimate limit on body size in flying animals
          • As bird size increases, volume increases faster than surface area
            • Maintain similar loading? = wings too large to control
        • Depends on flight style (e.g. soaring raptors have low wing loading for size)
    • Variation in flight style
      • Powered (flapping): Elliptical or high speed wings
        • Gliding (losing altitude) Any wing shape
      • Non-powered (no flapping or thrust)
        • Soaring (gliding with no altitude loss)
          • Static soaring (bird projected upwards by moving air): Slotted high-lift wings
            • Thermal soaring (on rising thermals)
            • Slope soaring (on rising air along a slope)
          • Dynamic soaring (bird uses wind speed gradients): high aspect ratio wings

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