birds 2 Flashcards
What advantages did the ability to fly give birds
1) predator escape
2) efficient foraging
3) fast locomotion (cost efficient)
4) allowed colonisation of remote habitats (islands)
5) allowed migrations instead of hibernations
- made birds successful and the most diverse group of terrestrial vertebrates
What are the constraints of flight in birds
1) requires major physiological + anatomical adaptations
2) compared to other vertebrates birds rather uniform in morphology
3) limited size + weight range , aerodynamics predict 12kg
4) Muscle power needed to take off increases by factor of 2.25 for each doubling of biomass
What are the origins of avian flight
1) Cursorial - running (stabilisation and/or catching flying prey )
2) Arboreal - from the trees down
3) WAIR - wing assisted incline running (could be earlier incarnation of arboreal hypothesis or combination of cursorial + arboreal)
4) Pouncing pro-avis hypothesis - using raptorial hindlegs in leaping ambush attack, -> selection for greater swooping range (alternative to cursorial)
Arguments for cursorial hypothesis
1) ambiguous morphological evidence of climbing abilities
2) lack of trees in locations where archaeopteryx was found
3) spread of feathered forelimbs was originally for stabilisation during running ( probably)
4) Archaeopteryx could probably glide, unlikely it could “flap”
Problems with the cursorial origin of fight
1) Max running speed 2 m/s, estimated min flying speed 6 m/s (velocity gap)
2) high energy demands of evolving flight (flight against gravity)
Evidence for arboreal evolution of flight
1) Hoatzin - “reptile bird” chicks have claws on two of their wing digits (enable chicks to climb trees until wings strong enough )
2) Feduclias’s claws are analysis - concluded that archaeopteryx was an arboreal. climbing bird that glided from heights
origin of feathers
1) feather first appeared in theropods (not birds) and probably did not evolve primarily for flying (symmetrical feather not aerodynamic)
2) Feathers are (probably) homologous of reptilian scales + different structures to hairs
3) Have non-flight functions : thermoregulation, colouration ,waterproof dressing
4) made of keratin (>90%) , (1%) lipid, (8%) water
Types of feather in extant birds
1) semiplume
2) down
3) filoplume
4) bristle
5) rectrices (tail feather)
6) remiges (wing feather)
What are the physical principles of flight
1) wings function as both aerofoil (lifting surface) and forward motion
2) shape, area + position can be modified
3) wings follow the principle of a cambereal airfoil
- bottom surface of wing pushes air forward and down, creating an area of high pressure below the wing and low pressure above it.
4) angle of attack = lift up to 15 degrees
aspect ratio
Aspect ratio (aeronautics) In aeronautics, the aspect ratio of a wing is the ratio of its span to its mean chord. Thus, a long, narrow wing has a high aspect ratio, whereas a short, wide wing has a low aspect ratio.
Wing functional types ( aspect ratio)
a) Dynamic soaring : high aspect ratio , make use of vertical wind gradient
b) Elliptral - low aspect ratio , highly cambered + high manouverability
cambered
camber is the asymmetry between the top and the bottom surfaces of an aerofoil. An aerofoil that is not cambered is called a symmetrical aerofoil.
How does “flapping” flight work
1 ) wing tips (primary feathers) responsible for thrust
- forward momentum from downward stroke of wings
- wings inclined from horizontal plane
2) small birds, upstroke = deceleration
How does ventilation work in birds
- birds have unidirectional air flow to receive a higher concentration of oxygen in their lungs than mammals
How do birds use colour + patterns
1) V important in sexual selection + crypsis
2)
