Flight and other locomotion in birds

Lift of a wing

• Bernoulli effect – pressure is inversely related to number of particles moving in a single direction (fluids).

• Newton’s 3rd Law – for every action there is an equal and opposite reaction.

Static airfoil (wing)

Angle of Attack

Vacuum

If angle of attack > ~5°, wing starts to produce vorticies. These can lead to “stall”

Solution = alula (bastard wing)

• Particularly important at low speeds and high angles of attack

A1°s

Open-billed Stork

Low Speed (take-off and landing)

High Angle of Attack

• Landing

• Sanz et al. 1996 Nature • Eoalulavis hoyasi• Los Hoyas, Spain• Goldfinch sized bird• 115mya• 30my after Archaeopteryx

• = low speeds• = high maneuverability

Florescent induced photo

Eoaluavis

Drag

• Resistance caused by friction of air moving over the surface of the wing

• Induced drag occurs when the air flow separates from the surface of a wing– Air moves from high to low pressures– “fills” vacuums created by wing

• Profile drag is due to the friction between the air and bird moving through the air– Minimized by “low profile” (aerodynamic anatomy)– i.e. thin leading edge of wing

Induced Drag• Di - induced drag

• A - aspect ratio

• k - constant

• L - lift

• S - wing area

• Ve - airspeed

• ρ - air density

Ve - Airspeed

Di -

dra

g

High speed Low speed

D is the force of drag, ρ is the density of the fluid*, v is the velocity of the object relative to the fluid, A is the reference area, and Cd is the drag coefficient

Profile Drag

Airspeed

D

Drag Curve

aka Profile drag

• 2 gaits of a bird– Vortex-ring gait

• Low speeds

– Continuous-vortex gait• High speeds

Flight Recap

• Amount of drag is affected by:– Body size– Speed– Wing’s surface area and shape– Environmental factors

• Viscosity etc.

Wing shape

• Aspect Ratio – Length / width– Range = 1.5-18.0

Gliding Wing

• Laysan Albatross

High Speed Wing

Explosive, Maneuverable Wing• Grouse Wing

Table of Wing loading – body mass / wing area

Species or group Wing-loading

Swallows 0.15

Passerines 0.2 - 0.4

Hawks 0.3 - 0.5

Waterfowl 0.8 - 1.0

Pied-billed Grebe 1.2

Loons 1.4 link

Wing loadinghighlow

Contribution of the hindlimbs• Varies over species

– May be very important (Starlings 80-90% of take-off velocity due to hindlimb contribution)

Earls 2000

• Hummingbirds– 46-59%– Variability

depends upon motivation

• Autonomous – 59%

• Escape – 47%

• Aggressive (chasing conspecific male) – 46%

Tobalske et al. 2004

The leading edge Vortex

• The “LEV” of a swift

Low pressure zoneOn top of wingWing wants to “fill” the low pressure zone thereby creating liftCan be used for maneuverability (each wing independent)

Videler et al. (2004)

Wing slotting

Different Modes of Flight

• 1. Gliding – Vs/V (sinking speed – horizontal speed)– Glide ratio of 20

• 2. Soaring – maintain altitude w/o flapping.– Thermals (see drawing) and updrafts (“slope soaring”)– Dynamic soaring

“Obstruction lift”Or “slope soaring”

• Hawk mountain

east

Kettle valley

Dynamic Soaring• 1 - climb

(windward flight);

• 2 - upper curve (change of flight direction to leeward);

• 3 - descent (leeward flight); &

• 4 - lower curve (change of flight direction to windward) (Sachs 2005).

video

3. Flapping flight

• Video of a starling in a wind-tunnel• Downstroke (“power stroke”) – flex wing depressors - lift.• Upstroke (“recovery stroke”) – flex wing elevators - minimize drag.

– Slotting

Cockatiel flying at 1m/sec

Flapping (cont)

• Flapping is usually intermittent in small species

• And varies w/ speed

Flap-glide Flap-bound

Budgerigars in wind-tunnel (Tobalske and Dial 1994)

4. Hovering

• Flapping while maintaining horizontal position• Examples:

5? Formation Flying

high

low

• Saves energy (11-14%)

• Coupled with full belly – even more (Kvist et al. 2001)

Note on metabolism and flight

Predicted

Observed

Other forms of locomotion in birds

• Running, walking, hopping, waddling– Head bobbing– Ostriches

• Climbing– Nuthatches, woodpeckers

• Swimming– Ducks

• Diving– Penguins, Auks