Flight in birds involves complex movements that have evolved through adaptations. Birds have developed specialized morphological and anatomical features for flight. Their bodies are lightweight with feathers, wings adapted as forelimbs, strong breast muscles, and pneumatized bones. Their circulatory and digestive systems are efficient. Wing shape and angle create lift through deflecting airflow. Birds flap their wings to provide both lift and thrust during flight. Perching involves flexor tendons and muscles enabling automatic grasping of perches.

1. Prof. Archana Das
Dept. of Zoology
Tangla College

2. Flight in bird is one of the most complex
forms of locomotion in the animal kingdom.
Flight in birds includes hovering, taking off
and landing which involves many complex
movements.
As different bird species have adapted to
specific environments and other basic needs,
they have developed different forms of wings
and varied forms of flight.
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3. Adaptations For Flight
Any alteration in the structure or function of an
animal or any of its parts that results from natural
selection and by which the organism becomes
better fitted to survive and multiply in its
environment is called as adaptation.
For flight, the body of birds has been well adapted
both Morphologically and Anatomically
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4. Morphological Adaptations
Body Contour
Spindle shaped body to
ensure least wind resistance.
High position of light organs
like lungs , air sacs and low
position of heavy muscles,
sternum, digestive system etc.
Low Centre of gravity in the
body.
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5. Morphological Adaptations
Presence of feathers
Makes the body stream-lined and reduces
the friction to the minimum.
Very light, hardly adds weight to the bird.
Serves as a blanket enveloping air around
the body and adds buoyancy.
Feathers of wings increases the surface
area for striking the air.
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6. Forelimbs Modified into Wings
Forelimbs of birds become modified into unique and
powerful propelling organs called wings which propel the
body high up in the air.
Mobile Neck and Beak
Mobile neck and beak enables the bird for feeding, nest-
building, offence and defense, preening, etc.
Bipedal locomotion
The hind limbs can support the body weight and acts as
locomotory organs on the ground
Morphological Adaptations
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7. Perching
Muscles are strongly developed and modified so that
when a bird sits in a perch, the toes automatically grips the
perch.
Short tail and Tail Feathers
Short tail and Tail Feathers can serve as a rudder during
flight and assist in steering, lifting and counterbalancing
of the body during flight
Morphological Adaptations
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Anatomical Modifications
Endoskeleton
Light and provides large surface
for attachment of muscles.
Bones are pneumatic filled with
air spaces and air sacs.
Skeletal framework is compact,
centralised and relatively rigid
due to fusion of bones.

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Muscles on the back are much reduced and flight muscles on
the breast are strongly developed
Flight Muscles
Anatomical Modifications

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Digestive Organs
Digestive system is efficient with a reduced rectum. In
birds the undigested food is never stored because it would
create extra burden of faeces.
Circulatory System
Heart is large in size and efficient to keep completely
separated the pure and impure blood.
Anatomical Modifications

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The shape of a bird’s wing is
important for producing lift.
The increased speed over a
curved, larger wing area creates a
longer path of air. This means the
air is moving more quickly over
the top surface of the wing,
reducing air pressure on the top
of the wing and creating lift.
The angle of the wing deflects air
downwards, causing a reaction
force in the opposite direction
and creating lift.
Wings

12. Basic Mechanism of Flight
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The fundamentals of bird
flight are similar to those of
aircraft. Lift force is
produced by the action of air
flow on the wing, which is an
airfoil. The lift force occurs
because the air has a lower
pressure just above the wing
and higher pressure below.
LIFT

13. Basic Mechanism of Flight
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GlidingWhen a bird is gliding, it doesn’t
have to do any work. The wings are
held out to the side of the body and
do not flap. As the wings move
through the air, they are held at a
slight angle, which deflects the air
downwards and causes a reaction in
the opposite direction, which is lift.
But there is also drag (air resistance)
on the bird’s body, so every now and
then, the bird has to tilt forward and
go into a slight dive so that it can
maintain forward speed.

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Basic Mechanism of Flight
Flapping
When a bird flaps, its wings continue to develop lift, but the lift is
rotated forward to provide thrust and it counteracts the drag and
increases its speed.
Flapping involves two stages: the down-stroke, which provides the
majority of the thrust, and the up-stroke, which can also
(depending on the bird’s wings) provide some thrust.

15. Basic Mechanism of Flight
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DragApart from its weight, there are 3
drag forces that resist a bird in
flight.
Frictional drag is caused by the
friction of air and body surfaces,
Form drag is due to frontal area
of the bird. It is also known as
pressure drag
Lift-induced drag is due to the
Wing tip .

16. Mechanism of flight
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During flight the wings become unfolded, stretched and raised
vertically upwards.
These then move downward and forward (down stroke) and
finally upward and backward (up stroke).
Downstroke is achieved by the action of pectoralis minor, so that
the wing is lowered down. The wing is raised by the contraction of
pectoralis minor, and other muscles.
During downstroke, the wing is thrust downward like an oar. It
moves forward and vertically upwards with little air resistance for
the next powerful downstroke. The body moves forward in
upstroke.

17. PERCHING MECHANISM
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Perching is actually
maintaining a typical
posture by the Birds
while taking rest on a
support.The muscles
involved in perching
are situated in the
thigh and calf of the
bird’s leg.
The tendons of the
perching muscles in
birds are extended
upto the four digits
in the hind limbs.
They flex the four
digits of birds in the
hind limbs around a
support.

18. Perching Muscles
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PERCHING MECHANISM
When the bird is still sitting on a perch and the legs are in the
same bent position, the extensor muscles in the leg remain
inactive to keep the claws locked around the perch. So, the
birds can even go for a sleep without the fear of falling.
The perching muscles of birds are modified in such a way that
the toes can flex round a twig when the bird sits on it. When
the bird sits on the support, the legs are bent and put the
flexor tendons on stretch which results in spontaneous
bending of the toes around the perch.

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To unlock the claws of the feet, birds have to raise its
body for the perching position. And after the body is
raised to straight posture, the bird gets ready for a
flight again.

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Thank You !