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Origin of birds

Flight Adaptation

Mechanism of Flight

Perching Mechanism

Modes of Flight

Type of Bills

Type of Feet

Reproduction

Migration

Economic Importance

Index of Species

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Birds Of The World

What is a bird?

Aves are warm-blooded,oviparous,feathered bipeds.The epidermal exoskelton is represented by feather and a few scales on the legs similar to those of reptiles.The forelimbs are modified as wings.The hindlimbs are attached forwards to balance the weight of the body.The endoskelton is mostly spongy containing air cavities so that the body becomes light.The bones of the skull undergo early ankylosis.Only the lower jaw,quadrate,columella and hyoid are movable.There is only one occipital condyle.The premaxillac are large and form most of the beak.In modern birds,there are no teeth.

Most of the vertebrae have heterocercal centra.The cervical vertebrae have small ribs fused with the transverse processes.The thoracic vertebrae are joined togather.A fused synsacrum is formed by the union of lumbar,sacral and a few caudal vertebrae.The terminal vertebrae usually fuse to form plough-shaped pygostyle.

There is a well-developed sternum with the keel.In flying birds,the clavicles are usually well-developed and are connected by an interclavicle to form furcula.Ribs are provided with uncinate processes.The fore limb has only three digits.The three metacarpals are fused and there are only two separate carpals,others fuse with the metacarpals to form the carpometacarpus.The thumb is often clawed.

The pelvic girdle is fused with the sacrum throughout its lenght.The ilium is long and extends far in front and behind the acetabulum.The pubis and ischium are directed backwards and there is neither the pubis nor ischiatic symphyses.In the hind limb the fibula is incomplete and almost united to the tibia.The proximal tarsals are fused wiyh the tibia to form a tibio-tarsus.The distal tarsals arefused with the second,third and fourth metatarsals to form a tarso-metatarsus.The first metatarsal is free.

In the digestive system,the gullet is dilated into a crop and the stomach is divided into a glandular proventriculus and muscular gizzard.Rectal caeca are present at the junctionof the intestine and rectum.A cloaca is also present.

The non-expansible lungs are provided with air-sacs which may extend into the bones.The trachea has bony rings.A special vocal organ in the form of syrinx is present.

The heart is four-chambered;the right auriculo-ventricular valve is muscular.There is only right aortic arch.The renal portal system is poorly developed.The red blood corpuscels are oval and necleated.

The brain has large cerebellum and cerebral hemispheres and the optic lobes are laterally displaced.The eyes are usually large and have sclerotic plates and pecten.The olfactory organs are poorly developed.The auditory organ has large curved cochlea.

The kidneys are three-lobed.The ureters open into the cloaca.There is no urinary-bladder.The right ovary usually atrophies while the right oviduct is rudimentary.Birds are all oviparous and lay large eggs containing large amount of yolk and albumen.They have double shell membrane and calcareous shell.During development,the embryo develops embryonic membranes,viz. amnion,allantois and yolk sac.

Classfication of Aves

Birds show less diversification than any other group of vertebrate animals.This singular uniformity of structure is imposed upon them by the demands of flight.The great homogeneity of birds;therefore,fails to present convenient external features,such as the teeth of mammals,for their classification.

Class Aves has been differently divided and here is given one of the schemes of classification:-

1.Extinct,archaic,Jurassic birds of Mesozoic age,about 155 million years ago.
2.Wings primitive,with little power of flight.
3.Tail long,tapering,lizard like,bearing two lateral rows of rectrices.
4.Each hand bearing three unfused and clawed fingers.
5.Skull with teeth in both jaws,embedded in sockets.
6.Vertebrae amphicoelous.
7.Tail with 18-20 free caudal vertebrae,without pygostyle.
8.Sternum without a keel.
9.Carpals and metacarpals free.
10.Thoracic ribs slender,without uncinate processes.
11.Abdominal ribs present.
12.Cerebrellum small.

1.Modern as well as extinct post-Jurassic birds.
2.Wings usually well-developedand adapted for flight,with few exceptions.
3.Tail short and reduced,with rectrices arranged in a fanlike manner.
4.Wing composed of 3 partly fused fingers without clawes .
5.Teeth absent except in some fossil birds.
6.Vertebrae heterocoelous in living forms.
7.Few caudal vertebrae free.Rest fused into a pygostyle.
8.Sternum usually with a keel.
9. Distalcarpals fused with metacarpals to form carpometacarpus.
10.Thoracic ribs usually with unicinate processes.
11.Abdominal ribs absent.
12.Cerebrellum large.

1.Extinct,Upper Cretaceous birds.
2.Jaws bear teeth.
3.Brain of the avian type.

1.Large flightless marine birds.
2.Sharply pointed pleurodont teeth,present in grooves rather than in sockets.
3.Vertebrae amphicoelous.
4.Shoulder girdle absent.
5.Sternum without a keel.
Example:Hesperornis.

1.Large flightless marine birds.
2.Whether teeth were present is not definite.
3.Neck vertebrae amphicoelous.
4.Shoulder girdle well-developed.
5.Sternum with a well-developed keel.

1.Modern big-sized,flightless,running birds,without teeth.
2.Wings vestigial or rudimentary;feathers devoid of interlocking mechanism.
3.Rectrices absent or irregularly arranged.
4.Pterylae are irregular.
5.Oil gland is absent,except in Tinamus and Kiwi.
6.Skull is dromaeognathous or palaeognathous that is,vomer is large and broad and interpolated between palatines.
7.Skull sutures remain distinct for a long time.
8.Quadrate articulates by a single head with skull.
9.Sternum keel vestigial,absent or flat,raft like.
10.Unicinate processes are vestigial or absent.
11.Tail vertebrae free.Pygostyle small or absent.
12.Scapula and coracoid are comparatively small and fused at an obtuse angle(more than a right angle).
13.Clavicles are small or absent.
14.Iium and ischium not united posteriorly except in Rhea and Emu.
15.Pectoral muscles poorly developed.
16.Syrinx is absent.
17.Male has a large and erectile penis;female has a clitoris.
18.Young are precocious.
19.Distribution is restricted.

    Order 1.Struthioniformes
    (Gr.-struthio=ostrich+form)

1.Legs strongly developed,each with two toes(3rd and 4th)with stunted nails.
2.Pubes form a ventral symphysis.
Example:Ostrich.

1.Each leg bears three clawed toes.
2.Ischia form a ventral symphysis.
Example:Rhea.

1.Forelimbs greately reduced.
2.Head bears a comb-like structure.
Example:Cassowaries.

1.Feathers simple,hair-like or bristle-like.
2.Wings vestigial.
3.Long bill with nostrils near the tip.
Example:Kiwi.

1.Giant birds,became extinct nearly 700 years ago.
2.Wings almost absent,beaks short and massive legs bearing 4-toes each.
Example:Moas.

1.Recently externimated,rather later than Moas.
2.Wings small but legs powerful and 4-toed.
3.Long bill with nostrils near the tip.
Example:Giant Elephant-birds.

1.Small terrestrail birds,not flightless but essentially great runners.
2.Sternum is keeled.
Example:Tinamou.

1.Modern,aquatic,flightless,with paddle-like wings or flippers.
2.Feet are webbed.
Example:Penguins.

1.Most modern usually small-sized,flying birds.
2.Wings well developed;feathers with interlocking mechanism.
3.Rectrices present and arranged regularly.
4.Pterylae are regular.
5.Oil gland is present.
6.Skull is neognathous that is,vomer is short and allowing palatines to meet.
7.Skull sutures disappear very early.
8.Quadrate is double-headed.
9.Sternum with a well-developed keel.
10.Unicinate processes are present.
11.Pygostyle is present.
12.Scapula and coracoid meet at a right angle or acute angle.
13.Clavicles are always well developed.
14.Iium and ischium are united posteriorly.
15.Pectoral muscles large.
16.Male has no copulatory organ.
17.Young are altricious.
18.Distributed all over the world.