Evolutionary origin of flight

Question 1

Benefits of flight

Answer 1

• makes less vulnerable to predators
• efficient foraging
• cost efficient (j/km) - especially gliders
• fast locomotion
• colonise remote habitats and islands
• migration across world

Question 2

Constraints on birds by flight

Answer 2

• uniform morphology compared to other taxa
• need to be light
• need high metabolic rate and body temp
• bill mush lighter, gizzard for crushing food (not jaws), streamlines, no teeth
• cannot exceed 12kg for flight

Question 3

Origins of flight hypotheses

Answer 3

H1 = cursorial theory - birds started by running on ground, using wings to stabilise then to catch prey
H2 = arboreal theory - climbs trees and other objects, gliding from heights
H3 = WAIR - wing-assisted incline running - can use height to protect selves, to glide and fly actively
H4 = pouncing pro-avis H - use wings for extra acceleration when going after prey

Question 4

Cursorial…

Answer 4

•archaeopteryx feathers suggest could fly
-joints not considered sufficiently flexible to support active flight - Archaeopteryx could glide
•spread of feathered forelimbs (wings) originally stabilised for running
-lack of trees where A found

Question 5

Problems with cursorial theory

Answer 5

•max running speed 2m/s - estimated min needed 6m/s
-velocity gap
-experiments test it acc could though…
•high energy demands of evolving flight - fighting against gravity
•problems of explaining origin of flight stroke in earthbound organism

Question 6

Support for Arboreal

Answer 6

•supported by hoatzin spp - lives in trees, has claws on wings can use for climbing trees
-similar claws to archaeopteryx and showed could be used for this locomotion
•A’s forewing fell among climbers, and hind wings amongst perching - supporting it could climb trees

Question 7

Origins of feathers

Answer 7

• first appeared in theropods
• homologues with reptilian scales - but different to hair
• flight not only function - display/colouration, thermoregulation and waterproofing
• made of B-keratin >90%, 1% lipids, 8% water and pigments
• barbs have tiny barbules with hooks, interlock between barbs = strong connections

Question 8

Different types of feathers

Answer 8

• remiges-wing feathers
• rectrices-tail feathers
• down - trap air
• contour feathers - typical body feathers
• bristles - help for sensory, catch prey etc.

Question 9

Physical principles of flight

Answer 9

•wings have to be aerofoil - lifting surface and forward motion - propeller
•shape, area and position can be modified
•bottom surface concave and upper is convex
-bottom pushes air forward and down, creating area of high pressure below wing and low pressures above (creates lift)
•retain 1 digit that has an alula, group of feathers to create slot reducing turbulence

Question 10

Flapping flight

Answer 10

• lift and drag together make flight a resultant force
• primary feathers give thrust
• secondary feathers closest to body create lift
• in flight, primaries twist more than secondaries = thrust

Question 11

Ventilation in bris

Answer 11

• unidirectional airflow
• into air sacs, trachea, sucked into lungs, into different air sac and out
• very efficient

Question 12

Colouration of feathers

Answer 12

•important in sexual selection and crypsis
•combination of pigmentation and structural characteristics - reflection of specific wavelengths depend on pigment particle size
-black = eumelanin
-red/brown = phaeomelanins
-red-yellow = carotenoids (from diet)
-UV sensitive = porphyrins
•layers in feathers and gaps between were precise wave-lengths of light are reflected = iridescence