Birds – Part III

VERTEBRATE ZOOLOGY (VZ Lecture25 – Spring 2012 Althoff - reference PJH Chapters 16-17)

Bill Horn

The Avian Wing

• Aircraft: have propeller to ‘bring through air’ andwings to serve as airfoil (lifting

surface)• Birds: wings function as both: ___________ &

_________• Propellar part mostly achieved by primaries on

downstroke as secondaries provide lift• Remove just a few primaries, bird’s ability to fly is

greatly reduced. Remove almost half of secondaries and bird can still fly.

Fig. 17-8 p444, PJH

1 2 3

Airflow around a cambered airfoil (wing)_________________ – the air streams smoothly

over the upper surface of the wing creating ____

less

air

pressure

above

Air moving faster here

Airflow around a cambered airfoil (wing)__________________ (steep)– the air passing

over the upper surface becomes ___________… decreasing lift enough to produce a stall

Air moving faster here

Airflow around a cambered airfoil (wing)_________________– the influence of the alula—

which forms a “wing slot”—helps to prevent turbulence by directing a flow of rapidly moving air CLOSE to the upper surface of the wing

Air moving faster here

Air Pressure

• If equal on dorsal and ventral surfaces of wing, then no lift if “symmetrically” streamlined wing

• Two ways to overcome this with the wings:a) increase the attack angle

b) bend the surface • Doing so, however, does increase drag (no totally

“free lunches here )

• A cambered airfoil (ventral surface of wing is concave, dorsal surface is convex) results in the air moving faster over the dorsal convex surface relative to the ventral surface

Camber

• Amount of camber possible in a wing varies by bird groups…depending on flight characteristics

• Camber also changes with ________ of the wing• Camber is greatest close to the body…and

decreases toward the wing tip. Therefore, the proximal portion of the wing generates ____________ than the distal part.

Stalling• When angle of attack reaches or exceeds about 150

(known as the stalling angle), no more lift is achieved by changing the attach angle of the wing.

• Turblence created as noted in

• Stalling can be reduced or prevented by slotting—created by the alula as noted in

• Slotting helpful during both _______ and _______• Overlapping of primaries also helps to smooth out

the flow of air over the one behind it—thus, acting as independent airfoils

2

3

Wing Tip Vortexes• = eddies of air created from outward flow of air

from under the wing and inward flow from over it• Results in _______________• One way to reduce this type of drag is to

____________ the wing which allows for widely separated tip vortexes

• Another way to reduce this type of drag is to ___________ the wing reduces the wing area at the tip where induced drag is the greatest

• Metric for this is the _______________ = ratio of length to width of the wing

Aspect Ratio = L/W

Length (L)

Width (W)

Aspect Ratio

swallow

Rough-legged hawk

Higher aspect ratio

__________________

• = mass of the bird divided by the wing area

• The lighter the loading, the less power needed to sustain flight

• Typically, smaller birds have lighter wing loading than larger birds. Variability, however, occurs related to the specialization for powered vs. soaring flight.

Wing Loading

Ruby-throated hummingbird

Barn swallow

Mourning dove

Peregrine falcon

Golden eagle

Mute swan

g/cm2

0.24

0.14

0.36

0.91

0.71

1.70

Flapping Flight

• Basically, an _____________ behavior….initial flights, although not very graceful, are usually successful.

• No precoccial species can fly right away…they can run but they cannot fly as further growth is needed to grow feathers and develop the flight muscles (i.e., pectoralis major and supracoracoideus)

• Altricial young don’t leave the nest until they can fly. Despite being reared in confined space (burrows, cavities, nest bowl) where they may not be able to stretch and exercise wing muscles much, they can fly…and far sometimes.

Diving Petrel: reared

in burrows. First

flight may be as far

as 10 km !!!

vs.

California condor

nestling spends

weeks “flapping”

wings” before 1st flight

Flapping Flight

• A beating wing is flexible…and porous…and yields to air pressure (unlike the fixed wing of an airplane)

• All these things can change as the wing moves through the cycle of locomotion:

a) shapeb) wing loadingc) camberd) angle relative to the bodye) position of individual feathers

…in other words, “lots of moving parts”

Flapping Flight…con’t

• Straight flight can only be achieved if a ______ is present to balance the drag operating against forward momentum

• The downward stroke provides the ________: * provided by ________…specifically the wing

tips• The ______ is provided by the inner wing:

* provided by the __________

Thrust & the Primaries

• Forces on the wing tips derive from two motions that are added together:

1) tips are moving forward with the bird and

2) tips are moving downward relative to the bird

• If the wing tips were not flexible, there would bea very large angle of attack and a stall

would result…to overcome this, forces on the tips of the individual primaries causes them to _______ as the wing is flapped downward

Thrust produces downward

stroke that results in….

…twisting of tips

of primary feathers

Vertical movement

of WING TIP

(primaries)

Vertical movement

secondaries

Flow of air

across the ___________

Resultant force

gravitational force

1 2

Flow of air

across

the w

ing

___________

___________

Resultant force

1 2

1 2 = FORWARD MOVEMENT

Result of these motions and forces acting on the inner wings and outer wings…

• The flow of air across the primaries is different than the flow of air across the secondaries and body

• When flight speed is through the air is constant, forces acting on the inner wing and body combine to produce a set of summed vectors in which ________________________ …and lift at least equals the body mass

We’re flying ahead when…

THRUST TOTAL DRAG

and

TOTAL LIFT M

M = gravitational force (ON BODY MASS)

L = total lift

Some other “details”….• As the wings move downward and forward in the

downstroke, as noted, the trailing edges of the primaries bend upward under air pressure….

….each feather acts as an individual ___________ biting into the air generating thrust

• Contraction of the pectoralis major produces the forceful downstroke during level, flapping flight

Some other “details”….con’t• During the upstroke (= return stroke = recovery

stroke), which is upward and backward, little to no thrust is achieved. It is considered a “________” recovery stroke and actually slows the bird down during this part of the wingbeat cycle

• This recovery stroke is powered by contraction of the supracoracoideus

For large birds…with slow wing actions:

• The upstroke lasts TOO LONG to spend in a state of deceleration…and a similar situation exists when when any bird takes off

• To overcome this, the bird must generate thrust on the UPSTROKE as well as on the downstroke. The upstroke thrust is achieved by:

a) _________ the wings slightly at the wrists &elbows

b) _______ the humerus upward and backward

Result: this movement causes the ____________ of

the twisted primaries to push air and produce thrust as

their lower surfaces did during the downstroke