FLIGHT ADAPTATIONS IN

BIRDS

UMESH BHARTI

ASSISTANT PROFESSOR

GOVT. COLLEGE FOR GIRLS

SECTOR-11, CHANDIGARH

A STRUCTURE THAT COMBINES

STRENGTH AND LIGHT WEIGHT

The evolution of flight has endowedbirds with many physical features

Wings and feathers.

Fusion and elimination of somebones

“Pneumatization" (hollowing) of theremaining ones.

Some of the vertebrae and somebones of the pelvic girdle of birdsare fused into a single structure, asare some finger and leg bones.

Hollow bones are connected to therespiratory system.

To keep the cylindrical walls of abird's major wing bones frombuckling, the bones have internalstrut-like reinforcements

BASIC MECHANICS OF BIRD FLIGHT

The fundamentals ofbird flight are similar tothose of aircraft.

Lift force is produced bythe action of air flow onthe wing, which is anairfoil.

The lift force occursbecause the air has alower pressure just abovethe wing and higherpressure below.

EVOLUTION HAS CREATED IN THE AVIAN

SKELETON A MODEL OF PARSIMONY,

LIGHTENING WHERE POSSIBLE

The bird skeleton is highly

adapted for flight. It is extremely

lightweight but strong enough to

withstand the stresses of taking

off, flying, and landing.

One key adaptation is the fusing

of bones into single ossifications,

such as the pygostyle.

The bird have a deep, solid

breastbone (sternum) to which the

wing muscles can be anchored.

PRESENCE OF SUPPORTING BARS AND

AIRSPACES IN BONES OF BIRDS

Photo by: Umesh Bharti

LIGHTWEIGHT BEAKS

Birds also lack teeth or

even a true jaw, instead

having evolved a beak,

which is far more

lightweight.

The beaks of many baby

birds have a projection

called an egg tooth, which

facilitates their exit from

the amniotic egg.

EFFICIENT RESPIRATORY SYSTEM

A bird's respiratory system isproportionately larger andmuch more efficient.

An average bird devotes aboutone-fifth of its body volume toits respiratory system.

The lungs of birds are lessflexible, and relatively small,but they are interconnectedwith a system of large, thin-walled air sacs in the front(anterior) and back (posterior)portions of the body.

Air sacs are connected with theair spaces in the bones.

BIRDS LUNGS OBTAIN FRESH AIR DURING

BOTH EXHALATION AND INHALATION

Birds' lungs are anatomically very complex (theirstructure and function are only barely outlinedhere), but they create a "crosscurrentcirculation" of air and blood that provides agreater capacity for the exchange of oxygen andcarbon dioxide across the thin interveningmembranes.

A breath of inhaled air passes first into theposterior air sacs and then, on exhalation, intothe lungs. volume.

Air passes through the lungs in both exhalationand inspiration, with the air sacs functioning asa reservoir for the next breath of air.

Avian lungs do not have alveoli, but insteadcontain millions of tiny passages known asparabronchi, connected at either ends by theand .

Air flows through the honeycombed walls of theparabronchi into air vesicles, called atria, whichproject radially from the parabronchi.

These atria give rise to air capillaries, whereoxygen and carbon dioxide are traded withcross-flowing blood capillaries by diffusion.

BIRD'S CIRCULATORY SYSTEM, WELL

EQUIPPED TO HANDLE THE RIGORS OF

FLIGHT.

A bird's heart is large, powerful

It is a four-chambered structureof two pumps operating side byside.

One two-chambered pumpreceives oxygen-rich blood fromthe lungs and pumps it out to thewaiting tissues.

The other pump receives oxygen-poor blood from the tissues andpumps it into the lungs.

This segregation of the two kindsof blood makes a bird'scirculatory system, like itsrespiratory system, well equippedto handle the rigors of flight.

MUSCLE POWER

The flight muscles of most birds are red in color ("dark meat")because of the presence of many fibers containing red oxygen-carrying compounds, myoglobin and cytochrome.

They are also richly supplied with blood and are designed forsustained flight.

LOSS OF RIGHT OVARY TO REDUCE WEIGHT

FOR FLIGHT

The male have two testeswhich become hundreds oftimes larger during thebreeding season to producesperm

The female's ovaries becomelarger, although only the leftovary usually functions.However, if the left ovary isdamaged by infection orother problems, the rightovary will try to function.

SHARP EYES & LARGER BRAIN

Birds have found many ways to streamline,lighten, or totally eliminate unnecessaryparts (like urinary bladders)

Birds have brains that are proportionatelymuch larger than those of lizards andcomparable, in fact, with those of rodents.

The brain is connected to sharp eyes, andhas ample processing centers forcoordinating the information receivedfrom them.

A bird's nerves can rapidly transmitcommands of the brain to the musclesoperating the wings.

SYNSACRUM FORMS A RIGID STRUCTURE

WHICH CARRIES THE WEIGHT OF THE HIND

END OF THE ANIMAL

The synsacrum is a skeletalstructure in which the sacrumis extended by incorporationof additional fused orpartially-fused caudal orlumbar vertebrae.

The ilium of the pelvis isattached to the synsacrum.

In birds, posterior to thesynsacrum there are usuallyonly a few free caudalvertebrae, on the end ofwhich lies the pygostyle.

Photo by: Umesh Bharti

The furcula ("little fork" in Latin) is a

forked bone found in birds, formed by

the fusion of the two clavicles.

Its function is the strengthening of the

thoracic skeleton to withstand the rigors

of flight.

A keel is an extension of the sternum

(breastbone) which runs axially along the midline

of the sternum and extends outward,

perpendicular to the plane of the ribs.

The keel provides an anchor to which a bird's

wing muscles attach, thereby providing adequate

leverage for flight.

UNCINATE PROCESSES OF THE RIBS

The uncinate processes of theribs are extensions of bone thatin birds project caudally fromthe vertical segment of each rib.

These processes help tostrengthen the rib cage of birdsby overlapping with the ribbehind them

They are also shown to have arole in respiration by increasingthe effectiveness of musclesinvolved in inspiration includingthe appendicocostal muscles

Photo by: Umesh Bharti

FEATHER

Bird feathers consist of a shaft with rows offine filaments (barbs) on each side.

The barbs themselves have finer filaments(barbules) branching from them.

THREE SETS OF FEATHERS

The bird's forelimbs, the wings, are the key to bird flight. Each wing has a central vane to hit the wind,

composed of three limb bones, the humerus, ulna and radius.

The hand, or manus, which ancestrally was composed of five digits, is reduced to three digits which

serves as an anchor for the primaries, responsible for the wing's airfoil shape.

The other set of flight feathers, behind the carpal joint on the ulna, are called the secondaries.

The remaining feathers on the wing are known as coverts, of which there are three sets.

AIR PASSES BETWEEN VANES AIR

RESISTANCE CLOSES VANES

The flight feathers overlap

in a way that lets air pass

between them during the

upstroke, so reducing air

resistance.

During the downstroke

the gap is closed so

offering maximum air

resistance and giving lift.

ASSOCIATION BETWEEN MUSCLE &BONE

FRONT VIEW OF SKELETON AND WING

MUSCLES TO EXPLAIN FLAPPING FLIGHT

4 Upthrust transmitted

from wing to coracoid5 Whole body

lifted

tendon of minor pectoral

muscle

2 Wing pulled down

keel

sternum

major pectoral muscle (depresses wing)

minor pectoral muscle (raises wing)

coracoid

3 Air resistance gives

upthrust on wing

1 Major pectoral

muscle contracts

EXERCISE TO SHOW THAT BONES OF BIRDS

ARE LIGHTER

Mammalian skull Avian skull

QUICK RECAP

WHAT IS THE ROLE OF:

Keel

Pectoral muscles

Wish bone

Pecten of eye

Feathers

Synsacrum

Pneumatic bones

MOST FREQUENTLY ASKED QUESTIONS

How is a bird's body adapted for flight?

Explain morphological adaptations of flight in

birds?

Give an account of physiological adaptations for

flight shown by birds?

Write a note on flight adaptations of birds?

REFERENCES

1.Adaptations for Flight.[Internet]cited 2006-May-09, Available from: http://www.stanford.edu/group/stanfordbirds/text/essays/Adaptations.htm

2. Hasting L.Your guide to animal/wild life, Birds. [Internet] cited 2006-May-09 Available from: http://animals.about.com/od/birdsastudyguide/a/introtobirds.htm

3. Bird flight.2006-May-10[Internet]cited 2006-May-09.Available from: http://en.wikipedia.org/wiki/Bird_flight