1. General avian structures: Feathers

2. General avian Structures
Feathers
Furcula (wishbone) made up of two fused clavicle bones
Forelimbs are modified as wings
Sternum is modified as a vertical cartilaginous structure called keel which anchor flight muscles
Lacks teeth and instead has a modified keratinized beak
Lacks a diaphragm
Has no bladder

3. Feathers
Evolved from reptilian scales for thermoregulation and courtship display; later adapted to flight

4. Types of feathers 1. Contour feathers – pennaceous feathers
2. Non contour feathers – plumaceous feathers

5. 1. Contour (pennaceous) feathers
These cover the entire body and functions for
1.) protection of the body against the sun, rain, injury
2) Insulation for thermoregulation
3) flight and
4) courtship (gives the bird it colour patterns)

6. 2 types of contour feathers
Flight feathers
i) found on the wings, remiges
ii) Found on the tails, rectrices
ii) Non flight – coverts – found on the rest of the body
Contour feathers are organised as tracts or pterylae.
Where two tracts meet, there are no feathers and these regions are termed apterylae

10. Calamus (quill) – the non-pigmented shaft of the feather embedded in the hair follicle.
Delineated by
The proximal umbilicus - origin, deepest with an opening
The distal umbilicus – at the beginning of rachis

11. Contour feathers have vanes with barbs, barbules and hooklets (barbicels)

12. Contour feather contd

13. Flight feathers Flight contour feathers categorised as Primaries
Secondaries
Tertiaries

16. Remiges Conventionally
primaries are labelled inside out
secondaries and tertiaries are labelled outside in
The primaries are longest and thinnest and are connected at the phalanges and carpometacarpus.
The secondaries are connected to the ulna
The tertiaries are connected at the humerus. They form a protection over the primaries and secondaries when the wing is folded.

17. Alula feathers – Are assymetrical flight feathers found at the distal phalanx of the “thumb” (1st digit). Are not as stiff as other flight feathers and are used to slow flight.

18. Rectrices Tail flight feathers
Only the central pair are attached via ligaments to the tail bones called pygostyle
The remaining rectrices are embedded into the rectricial bulbs, complex structures of fat and muscle that surround the pygostyle.
Rectrices are always paired, with most species having six pairs.

19. Non contour (plumaceous) feathers
Down feathers
Powder down feathers
Semiplume feather
Filoplume feathers
Bristle feathers

20. Down feathers Have soft rachis, barbs and barbules; no hooklets
Found below contour feathers
Function – trap a layer of air for insulation

21. Powder down feathers:
specialised and breaks off to give of keratin powder - used by birds to waterproof feathers.

22. Semiplume feather In between a contour and down feather
Has a rigid rachis but soft barbs and barbules; no hooklet
Gives structural support, insulation and sensory function

24. Filoplume feathers Thin hairlike Found all over the body
Rigid rachis, plumaceous feathers at tip
Function – sensory; detects air pressure to adjust flight

25. Bristle feather Thin hairlike
Found around the eyelids, nares, and mouth
Rigid rachis, plumaceous feathers at bottom
Function – sensory and protective

26. Growth of feathers Initiation Growth
Growth of feathers are initiated by synergistic effect of thyroxine and sex steroid hormones (estrogen and testosterone)
Growth
Grow from a follicle as a dark soft blood feather nourished by high blood supply and covered by a waxy sheath
As it matures, blood is cut off and sheath removed by the bird

27. Molting
Periodic Shedding of old feathers and replacement with new ones.
Occurs especially in temperate species
This occurs once or twice a year after breeding
Birds shed their bright breeding plumage to a duller non breeding plumage

28. Physiological process
Molting is usually triggered by photoperiod change (decrease in day length) that stimulate the pineal gland
The pineal gland secretes melatonin hormone
Melatonin hormone influences pituitary hormone Leutinising hormone (LH)
LH stimulate increase in progesterone leading to molting
Molting does not occur instantaneously to allow for flight and insulation

29. e.g. Indigo Bunting
Eastern North American bird (passeriformes)
Female

30. Males – winter, early spring

31. Males – later spring; beginning of breeding season

32. Male – breeding plumage - summer

33. Feather colours Due to the following pigments;
1. Melanin – brown-black pigment produced by skin melanocytes from the amino acid tyrosine (melanogenesis)
2. Porphyrins – yellow and green. These are heterocyclic compounds produced by the body as derivatives of amino acid glycine (reaction with succinyl CoA of TCA cycle).
3. Carotenoids – derived from plants and absorbed by the GIT. Yellow, red and orange

34. Flight See Adaptations for flight 1. Flight feathers
2. Have light hollow bones (with struts to strengthen bone)
3. Some bones are pneumatic;
they have their medullary cavities filled with air which communicate with lung air sacs
These are typically found in posterior cervical vertebrate; thoracic vertebrate; the pelvis, the coracoid, humerus and sternum.
small birds have none but large birds have many.
Diving birds such as the penguin also lack these medullary cavities.

35. 4. No teeth therefore no massive jaw bones
5. Lay eggs therefore do not carry a heavy fetus
6. Have no bladder
7. Weight centralised
8. Streamlined

36. Flight Flapping, Involves a downstroke (powerstroke) followed by
an upstroke (recovery)

37. Downstroke

38. Downstroke
Downstroke is the powerstroke since it generates the power for flight
On downstroke the pectoralis flight muscle, whose origin is the keel of sternum and which inserts ventrally on the humerus, contracts pulling the wing bone down

39. Three forces are experienced after generation of powerstoke during flight;
D, Horizontal Drag due to resistance by wind passing over the wing, slowing forward flight
R, Upward Resistance by air below the wing
L, a Net Force that lifts and propels the bird

40. Closer to the body the wing,
Due to differences in tilt of the wing, different parts of the wing have different net force orientation
Closer to the body the wing,
comprising the secondaries and tertiaries, the leading edge is held horizontal, the drag is horizontal, the resistance near vertical with the net lift force vertical, lifting the bird

41. D = drag force, R = resistance force L = Net force (lift and/or propel)

42. The tip of the wing
The tip of the wing, comprising the primaries, is tipped with the leading edge ventral , the drag force is directed more vertically, the resistance more forward and the net force is a forward thrust (propulsion) (see figure section y)

43. Upstroke or recovery
Is achieved by contraction of the supracoracoideus muscle originating from the sternum and inserting onto the dorsal humerus via its tendon that passes through the foramen triosseum (delineated by the coracoid, humerus and the scapula)
During upstroke, the feathers of the primaries part slightly to allow air passing through and hence reduce resistance to downward air flow and avoid downward force

44. Metabolic adaptations to flight
Flight is metabolically expensive and birds have adapted for this;[A flying bird expends times more energy than a running lizard].
The high metabolic rate necessary for flight that allows for maintenance of higher body temperature to compensate for cool air in flight

45. Birds have a highly efficient respiratory system
To facilitate this high metabolic rate, Birds have Adaptations the allow for efficient O2 exchange. These are:
Large heart relative to body size; the heart of a sparrow is 3 times that of a mouse
Birds have a highly efficient respiratory system
Is compact allowing efficient exchange
allows ventilation during both inhalation and exhalation
Has air sacs that store large amounts of air

46. Types of flights 1. Flapping (discussed) 2. Gliding 3. Soaring
4. Hovering

47. Flapping

48. Gliding (turkey vulture)

49. Gliding Simplest flight. Gliding is flight without wing flapping.
Low energetic requirements
A gliding bird uses its weight (mass) to overcome air resistance to its forward motion.
Thus large birds can glide (e.g. vulture, albatross etc;) small birds cannot.

50. Gliding has two components
The sinking speed, Vs . The speed at which the bird sinks
The flight speed, V the speed the bird moves forward

51. The higher the glide ratio, the better the glide
The glide ratio V/Vs ratio determines the distance moved forward for every unit of height dropped
The higher the glide ratio, the better the glide
E.g. The black vulture, an excellent glider, has a ratio of 20; for ever 20 meters flow forward, there is a loss of 1 meter of elevation.

52. Soaring
This is the use of updraft (rising) winds to keep the bird flying at the same elevation or rising
Updrafts may be caused by
1. A physical obstruction such as a cliff or hill, physical updraft
2. Due to uneven heating of air by the ground e.g. air over large fields warm faster than those over a forest cover. The warmer air then rises over cooler air, thermal updraft.
As warm air rises it cools down hence reason why soaring birds soar in circles to remain within the area and elevation of heating

53. Soaring……
Physical updraft

54. Thermal updraft

55. Hovering

56. Hovering

57. Hovering Birds flap to equalise forward flight with wind resistance
Enables the bird to stay in the same position e.g. kestrels, kingfishers, humming birds
Most energetically expensive form of flight
Most birds cannot hover
The humming bird is the best hover
Hovers with wings motion in a figure of 8 on it’s side
The only bird that can fly backwards.

58. Formation flying

59. Formation flying Why does it occur? To impress observers?
Some biological explanation?
Just plain creation?

60. It increases energetic efficiency of flight
Due to pressure differences on the wing surfaces – high below, low above; The preceding bird creates an updraft (vortex) of wind behind it and lateral to the wing tips.
The energy created called wake energy is then used by the bird just behind and lateral to it to facilitate it flight

62. Tail
Is used for steering, balancing (By angling left or right) breaking (angling down)

63. Landing

64. Landing
The tail feathers spread out creating a lift of the posterior and a depression of the neck and head.
Along with the gliding wings, there is then a decrease in altitude to land.

65. Landing

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