Bird belongs to the class Aves. They are warm-blooded vertebrates with wings, feathers, and light hollow bones. The vast majority of birds are capable to flight.
Average body temperature of a bird is 105°F or 40°C. There are
some slight variations among the different species. Surprisingly their body
maintains same temperature despite the temperature of the environment.
In cold temperatures, birds sometimes
struggle to maintain constant internal temperature. Due to less mass in their body,
it is difficult for the small birds to produce the required heat. Feathers are good
insulation and oil covering on them gives more protection. The scales on the
legs and feet gives protection against cold. Birds spending winter in cold
climates eat large amounts to add extra layer of fats.
The respiratory system of birds is different
from other vertebrates, having relatively small lungs plus nine air sacs that
play important role in the respiration. These are – Two Cervical Air sacs, One Interclavicular
Air Sac, Two Anterior Air Sacs, Two Posterior Air Sacs, Two Abdominal Air Sacs.
The air sacs permit a unidirectional flow
of air through the lungs. Unidirectional flow means that air moving through
bird lungs is largely “fresh air” & has higher oxygen content. These air
sacs store and pump air through stationary lungs. With the help of the air
sacs, this allows birds to take in oxygen even during exhalation.
Birds can breathe at much higher
elevations than mammals because of their more efficient lung structure.
Birds have many physical features, beside
wings, that work together to enable them fly. They need lightweight,
streamlined rigid structures for flight. The four forces which mainly affects
the flight of the birds are – weight, lift, drag and thrust.
Gravity pulls on birds, too. In order to
minimize the effects of gravity, birds are adapted to be as light as possible.
These are some adaptations that help makes bird light –
- Light weight smooth
feathers – these reduces the forces of weight and drag.
- A beak, instead of
heavy, bony jaws and teeth – these reduces the force of weight.
- An enlarged breastbone
called sternum for flight muscles attachment – these helps with the force of
thrust.
- Light bones – a bird’s
bones are basically hollow with air sacs thin, tiny cross pieces to make bones
stronger – these reduces the force of weight.
- A rigid skeleton to provide
firm attachments for powerful flight muscles – these helps with the force of
thrust.
- A streamlined body –
these helps to reduces the force of drags.
- Wings – these enables
the force of lift.
- Birds don’t have
bladders. Bird urinates as soon as it has to, getting rid of the useless weight.
Wings: The shape of the bird’s wings is important
for producing lift. The increased speed over a curved, larger wing area creates
a longer path of air. As a result, the air moves more quickly over the top
surface of the wing, reducing air pressure on the top of the wing and creating
lift.
Wing loading: How fast a bird fly to be able to maintain lift i.e.
*Wing Loading= Weight/Wing Area (Kg/Sq.m.)
Gliding: When a bird is gliding, it doesn’t
have to do any work. In gliding flight, a bird’s wing deflect air downward,
causing a lift force that holds the bird up in the air. There is also air
resistance and drag on the body and wings of the bird, so every now and then,
the bird has tilt forward and go into slight dive so that it can maintain
forward speed.
Soaring: It is a special kind of glide
which the bird flies in a rising current or a thermal. Because the air is
rising, the bird can maintain its height relative to the ground.
Flapping: Wings of the birds flap with
up-and-down motion at the right angle, which means the wings have to twist with
each downward stroke to keep aligned with the direction of travel.
Thrust: Birds obtain thrust by using
their strong muscles and flapping their wings. Some birds use gravity to give
them forward thrust to flight. Others may use running take-off from the ground
Different birds have different adaptive
features to meet their flight needs.
Birds Anatomy:
External Bird Anatomy
1. Beak: A birds beak consists of two mandibles: upper and
lower, each of bone core covered in a horn like sheath of compact epidermal or
skin, cells.
Upper mandible although not in all species,
rigidly attached to the skull such that it does not move, only the lower
mandible is free to move.
2. Eye: The main structure of the bird eye are similar to those
of the other vertebrates. The outer layer of the eyes consists of the
transparent cornea at the front and two layer of sclera – a tough white
collagen fiber layer which surrounds the rest of the eye and supports and
protects the eye as whole.
3. Wings: Bird’s wing act as both wing and propeller. The basal
part of the wing supplies most of the supporting surface, the wing tip most of
the propelling force. The tail of the birds act as a steering.
4. Feet: Bird’s feet and toes are made up mostly of tough
tendons and bones and are covered with heavily scaled skin. This scaly skin
helpful to prevent wear and tear due to walking and perching.
5. Tail: Bird’s tails end in long feathers called rectrices.
These feathers are used as a rudder, helping the bird steer and maneuver in
flight. They also help the bird to balance while it is perched.
6. Anus: Cloaca [Kloh-AY-KahL(Latin Word): a Sewer] the combined
opening of the digestive, urinary and reproductive systems of many vertebrates
including birds.
Internal Bird Anatomy
1. Brain: Birds brain includes: medulla - part of the brainstem:
includes neurons that controls heart rate, respiration and blood pressure.
Optic lobe - part of the midbrain- relatively large in birds compared to other
vertebrates.
2. Spinal Column: Spinal column of birds contains numerous and
well ossified vertebrae, and considerably more than six numbers of anohylosed
together to form sacrum. The vertebral column is divided into five sections of
vertebra:
I.
Cervical = Neck
II.
Trunk = Dorsal/Thoracic
III. Synsacrum = fused to Hips/Pelvis
IV.
Caudal = Coccyx
V.
Pygostyle = Tail
3. Trachea: Birds can breath through the mouth or the nostrils.
Air entering these openings during inspiration passes through the pharynx and
then into the trachea or windpipe( a tube about 4 inches long and less than an
inch in diameter). The trachea is generally as long as neck and its divides
into primary bronchi, each of which passes through lung and onward to the
paired abdominal air sacs; they also gives rise to secondary bronchi supplying
the other air sacs.
4. Esophagus: The pharynx is the part between the mouth and the
esophagus that helps the bird to swallow the food.. the esophagus is the tube
leading down from the pharynx to the crop.
5. Lung: The bird’s respiratory system consists of paired of
lungs, which contain static structures with surfaces for gas exchange, and
connected sir sacs, which expand and contract causing air to move through the
static lungs.
6. Crop: The crop is like a “doggy bag” when the bird eats. Many
birds eat as much as possible when the opportunity for feeding presents itself.
7. Gizzard: It is the muscular part of a bird’s stomach, which
is like a pouch, use to crush down their food. Birds with thick gizzards frequently
pick up grit – little stones, sand and small shells.
8. Kidney: Avian kidneys are made up of many tiny lobules. In
birds, are combined into three or more lobes. A bird has paired kidneys which
are connected to the lower gastrointestinal tract through the ureters. The
urine collected by kidney is emptied into the cloaca through the ureters and
then to the colon by reverse peristalsis.
9. Heart: Birds tend to have larger hearts than mammals relative
to the body size and mass. Bird have four chambered heart: two atria and two
ventricles, with complete separation of oxygenated and deoxygenated blood. The right
ventricle pumps blood to the lungs, while the left ventricle pumps blood to the
rest of the body. The cardiovascular system not only delivers oxygen to the
cells but also plays important role in maintaining a bird’s body temperature.
10. Liver: The liver is an important organ that is involved with
digesting food, storing and filtering the blood with many other metabolic functions.
Because it has so many functions, a healthy liver is most important.
11. Ureter: Nearly all bird species, there is no urinary bladder
per se. Although all birds have kidneys, the ureters open directly into a
cloaca which serves as a reservoir for urine, fecal matter and eggs. The ureter
of the birds is composed of a pars renalis which is connected to the kidney,
and apurspeltiica which runs from the caudal extremity of the kidney to the
urodeum.
12. Intestines: Birds have a small intestine that seems very
similar to the small intestine of mammals. A duodenum, jejunum and ileum are
defined.
13. Rectum: The cloaca is the common opening for the urinary,
reproductive and gastrointestinal tract of birds. It is divided into three
chambers: the coprodeum, urodeum and proctodeum . The coprodeum is the chamber
into which the rectum empties.
