Origin of Flight

Question 1

What are some advantages of flight?

Answer 1

Predator escape

Foraging

Cost-efficient locomotion as gliding is energy efficient

Colonisation - can access remote habitats inaccessible to other vertebrates such as islands

Migration - allows them to escape harsh environments in the winter

Question 2

What are some constraints of flight?

Answer 2

Requires major physiological and anatomical adaptations

Have to be rather uniform in morphology

Have limited size and weight - aerodynamics predict you have to be ~12kg to fly

Muscle power needed to take off increases by a factor of 2.25 for each doubling of biomass - when weight exceeds power limit you get flightless birds

Question 3

What is the cursorial theory?

Answer 3

Feathers evolved from the ground

Wings evolved to help running to catch flying prey such as insects

Question 4

What is the arboreal theory?

Answer 4

Flight evolved to move from top of trees to the ground

Wings helped movement around trees

Question 5

What is WAIR?

Answer 5

Wing-Assisted Incline Running

Wings evolved to assist in climbing

Question 6

What is an alternative hypothesis to the cursorial theory?

Answer 6

Pouncing Pro-avis hypothesis

Used wings to help jump/pounce on prey

So initially evolved to help hunt

Question 7

What are some arguments for the cursorial theory?

Answer 7

Ambiguous morphological evidence of climbing abilities

Lack of trees in locations where Archaeopteryx was found

Spread of feathered forelimbs (to wings) was originally for stabilisation during running

Archaeopteryx could probably glide but not probably flap due to the likely lack of flexible wrist

Question 8

What are some problems with the cursorial theory?

Answer 8

Velocity gap - max running speed for Archaeopteryx was 2m/s but studies show running speed needed to take off was 6m/s so 4m/s velocity gap

High energy demands for flight

Problem of explaining origin of the ‘flight’ stroke in an earthbound organism

Question 9

What is some evidence for the arboreal theory?

Answer 9

Claw on edge of the wing (not seen in modern birds like pigeons) - is seen in hoatzin chicks to help stabilise in trees

Same claw Archaeopteryx had

Ground species have flatter claws so Feduccias concluded Archaeopteryx was arboreal and glided from heights

But no trees found in Archaeopteryx environment

Question 10

Give some functions of feathers

Answer 10

Flight

Insulation

Sexual selection

Colouration

Water proofing

Question 11

Why do birds preen?

Answer 11

To keep barbules interlocked

Use oil from preen glands

Interlocking barbules maintain feather properties like insulation

Question 12

Give some types of feathers in extant birds

Answer 12

Wing feather

Down feather - fluffy and less structured and for insulation

Tail feathers - slightly asymmetrical so help with flight

Bristle feathers detect stimuli

Filoplumes for sensory purposes

Contour feathers

Semiplume feathers

Question 13

How do birds lift from ground?

Answer 13

Follow principle of aerofoil

Surface of wing pushes air forward and down

Creates area of high pressure below wing and low pressure above

Results in lift

Question 14

What type of air flow do birds have?

Answer 14

Unidirectional

Allows lower air capacity whilst maximising oxygen intake