General Characters and Flight or Aerial Adaptations’
in Birds
The birds get a living
by moving in the air , which is the most difficult medium of all and also the
most rewarding for freedom of movement. Birds are active animals. Flight
enables them to avoid their enemies and to seek new habitats. They low weight
and high power. The lightness and strength are achieved by using thin sheets
and tubes of bones and extending air sacs into them. There no teeth or heavy
jaws and the food eaten is quickly digested and of high energy value. Accumulation
of fat is very low. They have high temperature, metabolic rate rapid heartbeats
and high performance respiratory and muscular system.
GENERAL CHARACTERISTICS OF CLASS –AVES
1. Birds
are feather clad, warm blooded, and air breathing, oviparous, bipedal vertebrates.
2. Body
is boat shaped and divided into head, neck, trunk and tail.
3. Limbs
are two pairs. Fore limbs are modified into wings.
4. Exoskeleton
is epidermal and horny. Legs are covered by scales. No skin gland except oil
gland
5. Skin
is dry.
6. Endoskeleton
is spongy bones, light in weight containing air cavities.
7. Skull is monocondylic. Cranium is large and
sutures indistinct.
8. Lower
jaw is composed of five or six bones.
9. Modern
birds have no teeth. A horny beak is present.
10.
Vertebral column short.
11.
Vertebral ribs are double headed,
provided with uncinate process.
12.
Both clavicles and single interclavicles are
fused to form U or V shaped furcula.
13.
In pectoral girdle, the coracoids are
more or less pillar like.
14.
Pelvic girdle is large and elongated.
15.
In the leg, the ankle joint is inter-
tarsal.
16.
Lungs are spongy and non –distensible
with thin walled air sacs.
17.
The heart is four chambered. RBCs are
oval, nucleated and biconvex, warm blooded.
18.
Kidneys are metanephric and urecotelic.
19.
Eyes are large with nictitating membrane.
20.
Sexes are separate, fertilization is internal,
oviparous
21.
Parental care is highly developed.
a. Examples-
Sparrow, parrot.
Flight or Aerial
Adaptation in birds
Morphological
Adaptations
1. Body Contour
The birds have a
spindle-shaped body to offer less air resistance during flight. This helps the
birds to conserve energy and become more efficient at flying.
2. Compact Body
The body of a bird is
compact, dorsally strong and ventrally heavy to maintain equilibrium in the
air. Their wings are attached on the thorax, the light organs like lungs and
sacs are positioned high, the heavy muscles placed centrally are other features
that help in flight.
3. Body Covered With Feathers
The feathers are
smooth, directed backwards, and closely fitting which make the body streamlined
and reduce friction during flight. It lightens the body weight and protects it
from the effect of environmental temperature. They also have a wide surface
area for striking the air.
Feathers add to the
body buoyancy. It insulates the body and prevents any loss of heat from the
body. This helps the birds to bear low temperatures at higher altitudes.
4. Forelimbs Modified into Wings
The forelimbs are
modified into wings, which is the only organ of flight. These consist of a
framework of bones, muscles, nerves, feathers, and blood vessels.
The wings have a large
surface area. They also support the bird in the air. The wings have a thick,
strong leading edge with a concave lower surface and a convex upper surface.
This helps in increasing the air pressure below and reducing the air pressure
above. Thus the bird can fly upward and forward during flight.
5. Mobile Neck and Head
The birds have a long
and flexible neck, which helps in the movement of head important for various
functions. They possess a horny beak which helps them to pick the grains and
insects while feeding.
6. Bipedal Locomotion
The anterior part of
the body of a bird helps in taking off during flight. The anterior part of the
body also helps birds to land. The hindlimbs help in the locomotion on land.
They can support the entire body weight of a bird.
7. Perching
When a bird sits on the
branch of a tree, its toes wrap around the twig. This is known as perching. The
muscles are so well-developed that a bird can sleep in that position without
falling.
8. Short Tail
The tail bears long
feathers that spread like a fan and function as a rudder during flight. They
also help in balancing, lifting, and steering while flying and perching.
Anatomical
Adaptations
1. Flight Muscles
The well-developed
muscles control the action of the flight muscles. It weighs about 1/6th of the
entire bird. The flight muscles are striated. The muscles on the wings are
large. Other muscles help the above muscles in functioning.
2. ght and Rigid Endoskeleton
The birds have a very
stout and light skeleton. The bones are hollow, filled with air sacs. They are
provided with a secondary plastering to increase their rigidity. The bones are
fused and lack bone marrow.
The birds lack teeth.
The thoracic vertebrae are fused except for the last one. This plays an
essential role in the action of wings striking the air.
3. Diestive System
The birds have a very
high rate of metabolism. Therefore, food digests rapidly. The length of the
rectum is reduced because of the minimum undigested waste. They have no gall
bladder which reduces the weight of the bird.
4. Respiratory System
The respiratory system
of birds is designed in such a manner that the food is oxidised rapidly and a
large amount of energy is liberated. Since the metabolism rate is higher, a
large number of oxygen molecules are required by the body. For this, the lungs
are provided which occupy the entire space between the internal organs.
5. Circulatory System
Rapid supply of oxygen
is required by the blood due to rapid metabolism rate in birds. Therefore,
birds require an efficient circulatory system. Birds have a four-chambered
heart that performs double circulation. This prevents the mixing of oxygenated
and deoxygenated blood. Also, the birds contain a large amount of haemoglobin
in their red blood cells, which helps in the quick aeration of body tissues.
6. Warm Blooded
The temperature of the
body of a bird remains high and does not change with the change in the
environment. This facilitates the birds to fly at very high altitudes.
7. Excretory System
The nitrogenous waste
is converted to less toxic organic compounds such as uric acid, and urates.
They have no urinary bladder. The uriniferous tubules efficiently absorb water.
