Flight Adaptations In Birds - Key Features & Diagram for Zoology Students

 

Flight Adaptation in Birds- Key Points & Diagram 

In birds, every system or organ has been modified to some extent to support flight.

As a group, birds are more homogenous than any other vertebrates, because their major adaptive features are focused on ability to fly. 

The flight adaptations in birds can be divided into two types: 

I. Morphological adaptations. 

II. Anatomical adaptations. 

I. Morphological adaptations 

1. Shape

 Perfectly streamlined spindle-shaped body offering minimum resistance to wind without wasting energy.

Flight Adaptation in Birds Diagram

2. Compact body 

Having a compact body which is light and strong dorsally and heavier ventrally aids balance in the air.

The placement of organs in the body aids in a low centre of gravity such as,

a. Attachment of Wings high up on Thorax.

b. Lungs and air sacs which are lightweight organs, are placed higher in position.

c. Heavy organs are positioned low and central ( such as heavy muscles, and sternum ).

d. Digestive organs are placed in the middle of the attachment of two wings.

 3. Body covering of feathers 

Feathers are the distinguishing feature of birds. Feather development occur from integumentary feather follicles. The smooth, closely fitted and backwardly directed contour feathers give it a streamlined shape and minimise friction in the air.

The feather gives buoyancy by holding air around the body.

The feathers maintain temperature by perfectly insulating, avoiding loss of heat.

This way at high altitudes the temperature is regulated.

4. Modification of forelimbs into wings 

Forelimbs are modified into wings by the presence of special flight muscles.

Wings, due to the muscles can easily propel through air. This is done with the help of elongated flight feathers of Wings called remiges which in turn helps provide a broad surface for supporting the bird in the air.

The following are the modifications in wings :

a. Thick strong leading edge.

b. Convex upper surface and concave lower surface  ( this shape is called airfoil) causing a reduction in air pressure above and increasing the pressure below with minimum turbulence.

This helps in moving forward and upwards during the flight.

5. Short tail  

The feathers in the tail i.e. caudal feathers or rectrices are long and strong but light, arranged in a fan-like manner. 

It helps in :

a. Steering during flight ( changing direction ).

b. Suddenly check the flight.

c. Counterbalance in perching.

6. Beak 

The presence of a beak compensates for the conversion of forelimbs into wings.

The beak works as hands ( forelimbs ) for,

a. Picking up things.

b. Nest building.

7. Mobile neck and head 

The bird's neck is very long and flexible. Since birds use their beak for feeding, preening, nest building, offence and defence, the freedom of movement and its mobility are of great importance.

8. Bipedal locomotion 

Because of the absence of forelimbs, the placement of the hindlimbs is shifted anteriorly from the trunk to support the entire body weight during locomotion on land and water. 

As the flightless birds have retained the habit of walking on two legs they are relatively stronger.

9. Integument 

The skin of the pigeon is dry, loose, hard and thin. The loose skin is a modification for flight helping in the extensive movement of skeletal muscles.

II. Anatomical adaptations 

1. Large muscles of flight 

The flight muscles on the breast are greatly developed weighing nearly 1/6th of the whole bird. The major flight muscles are :

a. Pectoralis major: It is a strong muscle which helps in depressing or lowering the wing.

b. Pectoralis minor: Wings are elevated or raised by this muscle.

c. Foramen triosseum: The tendon of the pectoralis minor passes through the foramen triosseum and gets inserted on the head of the humerus. ( some other muscles are also there of less important )

2. Perching 

The bird's body is modified to support flight or arboreal life. At a height, if it lands on something (e.g. tree ) it can hold it tight by perching ( In perching birds - passerines, a tendon passing over the heel and inserting on the terminal phalanges, locks the toes in flexion around twigs even while the bird sleeps. As the knee and ankle joints bend  when the bird settles down to rest, tension on the tendon makes the toes curl under ) the bending of the leg ( hindlimbs) exerts a pull on the flexor tendons to grip the perch while they are resting or sleeping.

3. Light and rigid endoskeleton 

Many adaptations in bones have given the birds 'strength with lightness' ( by the " hollow girder principle" ) required for a successful flight.  The bird's entire skeleton usually weighs less than its plumage. 

The adaptations are :

a. Their bones are pneumatic with air sacs instead of bone marrow.

b. The skull bones are light and tightly fused.

c. The ' uncinate processes' of thoracic ribs hook together giving compactness by concentrating the mass, when in flight.

d. The fusion of the dorsal part of vertebrae provides a rigid fulcrum for the action of wings.

e. All birds can move their necks 180° . The 8-24 cervical vertebrae have saddle-shaped ( heterocoelous ) centra that allow free neck mobility compensating rigidity of the trunk, helping in the process of preening of feathers and food collection.

f. Shortening of the caudal vertebra and formation of pygostyle ( four free vertebrae plus several fused )give stability in air by controlling tail fan.

g. The fusion of the pelvis with synsacrum provides,

i. Firm attachment to the legs,

ii. Supports the weight of the body during the walk.

iii. During takeoff, it counteracts the effect of shock.

g. The absence of a mid-ventral symphysis of pubes and ischia results in a more posterior displacement of viscera, shifting the centre of gravity of the body towards hind legs and also helping in large calcareous egg laying.

h. During bipedal gait ( walking ), the fusion of distal tarsals with the metatarsals to form tarsometatarsus and the fusion of proximal tarsus with the lower end of the tibia to form tibiotarsus, helps to give more strength.

i. In flying birds, the sternum possesses, a large mid-ventral ridge or Keel for the attachment of major flight muscles whereas in running Birds ( flightless ratites ) the keel is absent e.g. ostrich. The sternum which is T-shaped also supports the abdominal viscera.

4. Digestive System 

In birds, 

i. rate of metabolism is - high

ii. food requirement - great

iii. digestion - rapid.

Food is high-caloric and with minimal undigested wastes, so the digestive system of birds is compact, where the rectum is short as the faecal matter is relatively small and gets rid of very fast, reducing the body weight.

5. Air sacs and respiration :

The Respiratory system of birds have a system of air sacs, adjusting in between the internal organs and cavities of hollow bones. 

They help with internal respiration by aeration of the lungs thus regulating the body temperature.

Respiration in birds is effectively accomplished as there is no remaining residual air.

6. Warm bloodedness 

The temperature of the body ( 40°-46° ) is of great importance in birds as it controls their energy levels over a longer period during flight.

7. Circulatory system 

Birds being warm blooded require large oxygen supply and an effective circulatory system.

They have a four chambered heart with double circulation of blood. The blood has got a high level of hemoglobin in RBCs which is required for quick and perfect aeration.

8. Ureotelic excretion 

To reduce the body weight, the birds,

a. Do not have a urinary bladder.

b. Water of excretory fluid is reabsorbed in urinary tubules of kidney and coprodaeum of cloaca, forming semi solid excreta containing uric acid and urates, thereby reducing body weight.

9. Brain and sense organs 

In birds, the sight is more sensitive than smell, accordingly the eyes are larger with large optic lobes.

Eyes occupy a large portion of the head. The accommodating power is well developed as they can rapidly change from distant to near vision which is needed during flight.

Also they show a delicate sense of equilibrium and great power of musculature coordination because of the much convoluted cerebellum. 

The enormous development of corpus striatus in cerebrum also helps to attain stability in flight by great manoeuvrability.

10. Reproductive system 

Presence of the single functional ovary of the left side in the female bird leads to reduction of weight needed for flight.

Multiple Choice Questions (MCQs)

1. Tick the characters representing flight adaptation in birds.

a. Pneumatic bones

b. Sternum with keel for attachment of flight muscles
c. Forelimbs are modified into wings

d. All of the above

Answer: (d) All of the above ​

2. Significance of hollow bones in birds.
a. Increase body weight
b. Reduce body weight for flight
c. Decrease flexibility
d. Improve vision

Answer: (b) Reduce body weight for flight ​

3. Birds move their neck frequently because:
a. Their eyes are fixed and cannot move independently
b. They have weak neck muscles
c. Their vision is poor
d. Their ears are located far apart

Answer: (a) Their eyes are fixed and cannot move independently .

4. Which feature is most responsible for making flight possible in birds?
a. Thick skin
b. Heavy muscles
c. Light, streamlined bodies
d. Large beaks

Answer: (c) Light, streamlined bodies ​

5. The birds tail feathers function as:
a. Propeller
b. Rudder
c. Cushion
d. None of the above

Answer: b. Rudder ​

6. Besides pneumatic bones, another useful flight adaptation in birds is:
a. Syrinx
b. Pygostyle
c. Furcula
d. Quill feathers

Answer: (d) Quill feathers ​

7. Ostrich, penguin, and kiwi are:
a. Migratory birds
b. Four-toed birds
c. Flightless birds
d. Running birds

Answer: (c) Flightless birds ​

8. Birds have air sacs in their respiratory system mainly to:
a. Store food
b. Reduce body temperature
c. Facilitate efficient oxygen uptake during flight
d Protect internal organs

Answer: (c) Facilitate efficient oxygen uptake during flight.

9. What is the main adaptive benefit of a bird’s streamlined body?
a. help in swimming
b. less air resistance during flight

c. to maintain heat
d. help in camouflage

Answer: (b) less air resistance during flight.

​

10. Which of the structure is NOT an adaptation for flight in birds?
a. Modified wings
b. Light skeleton
c. Compact body
d. Toothless jaws
Answer: (d) Toothless jaws ​

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