Origin of flight

Question 1

List some advantages of flight

Answer 1

Escape predator
Foraging
Cost efficient locomotion
Colonisation
Migration → escape harsh conditions during winter

Question 2

Describe the cursorial theory of flight

Answer 2

• Ground based
• Wings used for running/stabilisation
• and/or catching flying prey e.g insects

Question 3

Describe the Arboreal theory of flight

Answer 3

• Started in the trees, gliding down
• Stability and locomotion

Question 4

Describe the WAIR theory of flight

Answer 4

Wing assisted Incline Running
- Add on to aboreal theory
- Idea that wings assist in climbing trees

Question 5

Describe the Pouncing Proavis theory of flight

Answer 5

Alternative to Cursorial
Idea that ancestral forms could’ve used wings to help pounce on prey

Question 6

Historically, which theory of flight has been favoured and why?

Answer 6

Cursorial
- Ambiguous morphological evidence of climbing abilities
- lack of trees where Archaeoptryx was found
- Spread of feathered forelimbs probably used for stability when running

Question 7

What are the problems with the cursorial theory of flight?

Answer 7

• Velocity gap
  Using physics and biomechanics, we know Archaeopteryx would need 6 mph to take off from the ground (but has 2 mph)
• High energy demands of flight
• Problem of explaining origin of the flight stroke in an earthbound organism

Question 8

Give some evidence for the arboeral theory of flight

Answer 8

• Extant Hoatzin chicks retain claw to help climb trees
• Similar claw found in Archaeopteryx
• Could be evidence for arboreal hypothesis
• However, still no trees where A has been found → bit of a mystery ?

Question 9

Describe the form and origin of feathers

Answer 9

• First appeared in theropods
• Did not evolve for flying
• Homologues of reptilian scales
• Flight is only one part of their function, even in extant birds (Thermoreg, display, sexual selection and signalling)

Question 10

Describe how wings follow the principle of aerofoil

Answer 10

• Wing surface pushes the air forward and down
• Creating an area of high pressure below the wing and low pressure above it
• Resulting in lift

Question 11

Describe how wings produce forwards momentum

Answer 11

Wing tips (primary feathers) responsible for thrust, leading to a forward momentum at downward stroke

Question 12

What is the aspect ratio of bird wings? and what does this mean?

Answer 12

Aspect ratio = length to width ratio

Question 13

Describe bird respiration, what does this mean for oxgyen content?

Answer 13

• Unidirectional air flow in bird lungs
  = higher O2 conc. than in mammals (to deal with the physiological demands of flight)

Question 14

Name some pigments birds use

Answer 14

Melanin (black/grey), pheomelanin (red/brown), carotenoids → must be obtained from diet (red/yellow)

Question 15

How is iridescence created in birds?

Answer 15

By layers of melanin granules inside the feather