Transcript Ppt - Department of Vet. Anatomy And Physiology

GENERAL AVIAN STRUCTURES:
FEATHERS
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
Feathers
 Evolved from reptilian scales for
thermoregulation and courtship display; later
adapted to flight
Types of feathers
 1. Contour feathers – pennaceous feathers
 2. Non contour feathers – plumaceous
feathers
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)
• 2 types of contour feathers
1.
Flight feathers
i) found on the wings, remiges
ii) Found on the tails, rectrices
2. 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
 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
 Contour feathers have vanes with barbs,
barbules and hooklets (barbicels)
Contour feather contd
Flight feathers
 Flight contour feathers categorised as
 Primaries
 Secondaries
 Tertiaries
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.
 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.
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.
Non contour (plumaceous)
feathers
 Down feathers
 Powder down feathers
 Semiplume feather
 Filoplume feathers
 Bristle feathers
Down feathers
 Have soft rachis, barbs and barbules; no hooklets
 Found below contour feathers
 Function – trap a layer of air for insulation
 Powder down feathers:
 specialised and breaks off to give of
keratin powder - used by birds to
waterproof feathers.
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
Filoplume feathers
 Thin hairlike
 Found all over the body
 Rigid rachis, plumaceous feathers at tip
 Function – sensory; detects air pressure to
adjust flight
Bristle feather
 Thin hairlike
 Found around the eyelids, nares, and mouth
 Rigid rachis, plumaceous feathers at bottom
 Function – sensory and protective
Growth of feathers
 Initiation
 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
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
 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
e.g. Indigo Bunting
 Eastern North American bird (passeriformes)
Female
Males – winter, early spring
Males – later spring; beginning of breeding season
Male – breeding plumage - summer
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
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.
• 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
Flight
 Flapping,
 Involves
 a downstroke (powerstroke) followed by
 an upstroke (recovery)
Downstroke
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
 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
 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
D = drag force, R = resistance force L = Net force
(lift and/or propel)
 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)
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
Metabolic adaptations to
flight
 Flight is metabolically expensive and birds
have adapted for this;[A flying bird expends
15-20 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
 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
Types of flights
 1. Flapping (discussed)
 2. Gliding
 3. Soaring
 4. Hovering
Flapping
Gliding (turkey vulture)
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.
 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
 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.
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
Soaring……
Physical updraft
Thermal updraft
Hovering
Hovering
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.
Formation flying
Formation flying
 Why does it occur?
 To impress observers?
 Some biological explanation?
 Just plain creation?
 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
Tail
 Is used for steering, balancing (By angling
left or right) breaking (angling down)
Landing
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.
Landing
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