Origin of Flight Flashcards
What are the advantages of flight?
- Predator escape
- Foraging
- Cost-effective locomotion (gliding)
- Colonisation
- Migration - not found in many other groups of verts
What are the constraints of flight?
- Physiological & anatomical
- Uniform morphology (most bodies are very similar)
- Max weight for flying birds = 12kg
- Muscle power needed to take off increases by factor of 2.25 for each doubling of biomass
Which clades of animals had feathers?
- Dromeosaurs
- Birds
- Some theropods
What are the two main theories for the origin of flight?
- Cursorial theory - used for running (stabilisation) - also aided hunting (ground based theory).
- Arboreal theory - used for stabilisation in the trees (gliding) (tree based theory)
What are the other less accepted theories for the origin of flight?
- 3rd theory: Wing assisted incline running WAIR:
- Wings evolved to assist in climbing
- Modern birds use their wings to aid in tree climbing
- 4th hypothesis: Pouncing Pro-avis Hypothesis
- Alternative to the cursorial theory
- Wings evolved to assist in hunting
- Jump/pounce on prey
What is the Raptor Prey Restraint model (“ripper”) behavioural model?
- Falls under the theory that wings evolved to aid hunting
- Pin down prey to facilitate hunting
Why was the cursorial model for the origin of flight favoured?
- Ambiguous morphological evidence of climbing abilities
- Lack of trees in locations where Archaeopteryx was found
- Spread of feathered forelimbs (⇒ wings) was originally probably for stabilisation during running
- Archaeopteryx could most probably glide, but its ability for flapping flight is in doubt, due to the lack of flexible wrists.
What are the problems with the cursorial theory ?
Origin of flight
- Velocity gap
- High energy demands of flight
- Problem of explaining origin of the flight stroke in an earthbound organism (how could they have lifted themselves off the ground)
What is the velocity gap?
Origin of flight
- Max running speed of Archaeopteryx was around 2m per second
- 6m per second would be needed in order to take off
What evidence is there for the arboreal model?
- Some extant birds maintained claws on end of wings used for climbing on trees, similar to that seen in Archaeopteryx.
- No tree found near Archaeopteryx so what was the claw used for?
- Pigeons have allula - separate small feather on the end of wing (where claw would have been?)
What is the Feduccia’s claw arc analysis?
- Compare many species
- Compare different habitat niches (ground, perchers, climbers)
- Compared Archaeopteryx with the different species claws
- Concluded that Archaeopteryx was arboreal
- Archaeopteryx: Front claw was similar to climbing birds - rear claws similar to perching birds
What is the origin of feathers?
- First appeared in theropods
- Did not evolve for flying
- Homologous of reptilian scales
- Very different from hair
- Flight is only part of the function
What are the features of feathers?
- Hollow shaft (calamus)
- Barbules - stick to each other via tiny hooklets
- maintain waterproof properties of plumage
- Air can circulate but water cannot get in
What are the different types of feathers?
- Wing
- Down
- Tail
- Contour
- Semiplume
- Filoplume
- Bristle
What is unique about the common poorwill bird?
Feathers
- Sensory feathers
- Feathers (bristles) around beak that detect prey
- Go into torpor at unstable conditions
What is the physical principle of flight?
- Wings function as aerofoil: lifting surface
- Provide forward motion (propeller)
- Shape surface and position can be modified
How does air move around the wing during flight?
- Air at the top of the wing moves slower than the air at the bottom
What part of the wing is responsible for thrust?
- Wing tips (primary feathers)
- Leading to a forward momentum at downward stroke
What is the principle of aerofoil?
Flight mechanism
- Surface of the wing pushes air forward and down
- Creating an area of high pressure below the wing and low pressure above.
- Creates an upward motion -Resulting in lift
What is the aspect ratio in wings?
- Length to width ratio
- Can be a strong indicator of the type of flight displayed by the birds
How do birds repsire ?
- Unidirectional air flow in lungs
- Higher oxygen concentration than animals
- Don’t exhale
- Important in flight
How does Unidirectional respiration benefit birds?
Minermises the energetic expendature
What are colours and patterns of feathers used for in birds?
- Important for sexual selection
- Crypsis
- Pigments - melanin, femelanin, keratinoits.
- UV sensitive
- Iridescent - very important in sexual selection
- Colours not only coming from pigments but also the structure
Why are feathers important in insualtion
- Some wing colourations (black to white) conducts heat and helps with lift and flight
- Darker wings are better at maintaining heat than lighter
