Lecture notes
Flight Anatomy of Birds
- Module
- Birds (BI2EY5)
- Institution
- University Of Reading (UoR)
Forces, Flight Styles, Wing Shapes, Skeletal, Muscular and External Anatomy.
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BirdsWeek 4
Chris Foster
Flight Anatomy
Key Adaptions;
- Feathers/ light skeleton relative to strength/ continuous gas exchange for respiration/
constrains form and function
Forces;
- Mass/ Lift [weight is the main constraint]/ Thrust overcomes Drag [must balance
forces to become and remain airborne]
- Bernoulli’s Law; [mid 1700’s- conservation of energy= kinetic and potential energy
within a system must remain constant]: static pressure + dynamic pressure = total
pressure.
- Creating Lift;
1. Static pressure; uniform force exerted in all directions by molecules [EG. Inside
balloon / Acts equally above and below the wing]
2. Dynamic pressure; pressure of moving air [bird manipulates moving air with
aerofoil wing]
o Air above the wing flows faster with lower pressure
o Air below the wing is at higher pressure
o Creates pressure gradient = lift [faster forward motion increases lift]
o Asymmetrical aerofoil; moving air created dynamic pressure/ shape constricts
flow above./ dynamic pressure above increases, static decreases/ no change in
static below, difference =lift
- Angle of Attack;
o Lowering angle of attack below horizontal generates negative lift [increasing
angle = increases lift] = turbulence
- Anula;
o Restores laminar flow over wing/ reduced turbulence at high angle of attack
o Greater lift from angle without reduced lift due to turbulence
o For landing and hovering
- Drag and thrust;
o Drag is friction between air and moving body [act as parachute]
o Thrust propels a bird forwards [created in flapping flight] / thrust on
downstroke/ more thrust = acceleration and ascent.
o High lift from extended wing but flexed wing reduces drag.
- Wing beats;
o Hypothetical; forward thrust of upstroke cancels our rearward thrust of
downstroke. Asymmetrical flapping fixes this.
o Primaries produce thrust and some lift, unbroken surface on downstroke [air
pressure forces broad inner vane against outer vane of feather above it] but
open on upstroke. [air pressure twists primaries open, air passes through]
o Secondaries produce lift.
o Flapping flight; 50 muscles, 100’s feathers, twisting primaries prevent stalling
- Hovering;
o Powered flight and controlled air flow = Anula / Hover into the wind.
, Birds
Week 4
Chris Foster
o Heaviest hover; pied kingfisher hover in no wind [80g]
o Largest eagle; black-chested snake eagle.
o Hummingbird hovering;
moves wings in unique pattern, lift on upstroke and downstroke,
primaries elongated, specialized joints = wings twist.
Manus; longer, make up 75% of wing rather than normal 50%
- Wing Loading;
o Ratio of body mass to wing area [tells us how much load each unit area must
carry]
o Large soaring birds have lower wing loadings
Canada Good; 2g/cm2
Ruby throated hummingbird; 0.24g/cm2
Leach’s storm petrel; 0.11g/cm2
- Turbulence;
o Movement causes turbulence, caused by friction of feathers, occurs close to
wing tips or feathers = interrupts laminar flow
o Turbulence = drag [use more energy to overcome it]
o Tip vortex caused by air flowing from low pressure above the wig to high
pressure below = creates free lift in V formation
o Long/ narrow wings over come it as lift-to-drag ration increased / have narrow
wing tips so less pressure above and below.
Broad rounded wings create high turbulence and heavy wing loads
- Slotting;
o Gaps between the feathers at wing tips also reduce turbulence, produces a
series of mini wing-tips where vortices are smaller = increases lift.
o Reduce vortices by bounding flight in small birds [woodpecker/ hornbill]
Flight Styles and Wing Shapes;
- Selection acts to reduce energetic demands, wing shape affects efficiency, long and
narrow is most efficient but has poor maneuverability.
- Aspect ratio; wingspan and wing depth /Dynamic VS static soaring
- Basic Shapes;
1. Elliptical;
o Good for maneuvering – variable
o Short and broad = low aspect ratio, slow flight, rapid take off
o Broader reducing wing load = Found in forest [increase maneuverability but
reduced aerodynamics] and shrubby areas [slightly longer wings, loses
maneuverability but gains aerodynamics].
2. High Speed;
o Tapered, pointed and swept back = low drag. / narrow tip = reduced
turbulence.
o Energetically expensive = constant flapping
o High aspect ration [short for length]/ speed and control for hunting and
migration
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