Ornithology Unit 3

Flight

Flight Variations

• Some birds can hover

• Some birds can dive

More Flight Variations

• Some fly in heavy brush

• Some soar for days on end

Avian Skeleton

• The avian skeleton is strong and delicate, a combination that allows them to fly

Skeletal Adaptations for Flight

1. Hollow bones – make them lighter

2. Bones are fused together and reinforced – makes them stronger

3. Have unusual joints – make flight motions possible and brace against stress

More Skeletal Adaptations

4. Instead of a heavy jaw and teeth, they have a toothless bill - makes them lighter

More Skeletal Adaptations

5. The sternum (breastbone) has a special structure called a keel – major flight muscles are anchored here

- Flight ability is directly related to keel size

More Skeletal Adaptations

6. The skeleton must be able to withstand the stress of flight.

- They have a lot of reinforcing in the thoracic area

- Have partially fused vertebrae

Furcula

• AKA, the wishbone• Made of fused collar

bones• Works like a spring &

helps bring the wings back up after the downstroke

The Wing

• A modified forelimb for flight

• Humerus, radius and ulna are similar to ours

• Fused hand, finger and wrist bones provide strength and rigidity to the outer wing

Flight Muscles

• Pectoral – power for down-stroke

• Supracoracoideus – brings wings back up

Flight Forces

• Negative Forces

1. Gravity

2. Drag

• Positive Forces

1. Lift

2. Thrust

Aerodynamics

• A bird’s wing is shaped like an airfoil

• Airfoil – an asymmetrically curved structure that tapers at the end

• Airfoils change the speed air flows over the surfaces and creates lift (or drag)

Generating Lift

• The amount of lift generated depends on surface area of wings and air speed

• It also depends upon the “angle of attack”

• More lift is generated as the back of the wing is tilted downward

Slots Between Flight Feathers

• Aid in fine control of air movements

1. Some help to maintain lift at slow speeds

2. Air forced through from the underside, expands as it hits the top of the wing, reduces pressure and increases lift

Wing Shape

• This effects the type of flying that can be done

• Pointed wings generate less lift, produce less drag (speed)

• Rounded wings produce more lift and drag (less speed)

More on Wing Shape

• Aerial and open country birds like shorebirds, swallows and terns have long pointed wings

• Birds living in thick vegetation usually have short rounded wings

Energy Costs

• Flight costs quite a lot of energy

• It can be defined by the relationship between the total wing area and total body mass

• This relationship is called wing loading and is given in grams per square centimeter of wing surface area (g/cm2)

Calculating Wing Loading

Sample Problem: The Osprey

Information: weight = 1500g

wingspan = 165 cm

body length = 56 cm

Step 1 Calculate the Wing Width

Surface Area = Length of Wing x Width

- We don’t know the width, so we’ll need to calculate it. Cornell Lab of Ornithology says a reasonable estimate can be calculated by multiplying the body length by 1/3 (0.33). So…

- Wing width (w)=body length (b) x 0.33 or

- w=b x 0.33 so w=56cm x 0.33=18.48cm

Step 2 – Calculate the Surface Area of the Wing

Surface area = wingspan(s) x wing width(w)

so…

SA = S x W or

SA = 165cm x 18.48cm

SA = 3049.2cm2

Step 3 – Calculate the Wing Loading Ratio

Wing Loading(WL) = Mass (m) / SA

WL = m / SA so for the osprey…

WL = 1500g / 3049.2cm2

WL = 0.49g/cm2

Gliding Flight

• Flight that takes place without flapping

• Without flapping, no forward thrust is applied, so they sink because of drag

Thermal Soaring

• Uses columns of warm air rising from the ground from the sun heating the earth

• Circle in one “thermal” and rise, then glide to the base of another

Slope Soaring

• Using rising air deflected off of a ridge or ocean wave

• Migrating hawks soar along ridges and gulls are able to hang in the air behind a boat

Flapping Flight

• Flapping adds thrust

• Wings push air down and back

• Some flap constantly, others have an undulating flight pattern

• Independent control of each wing helps with steering

• The tail is also used to generate some lift and also for steering

Flightless Birds

Q: Why are some birds flightless?

A: They avoid the cost of developing and maintaining complex structures used for flight

- Flightless birds typically fill other niches (environmental roles) than flying birds

- Develop special adaptations for their niche