Class Aves – Class 11 | Chapter – 4 | Short Notes Series PDF

Class Aves: Aves are a class of endothermic vertebrates, commonly known as birds. These animals fall under the phylum Chordata carrying specific features such as toothless jaws with beak, laying of eggs with a hard shell, etc. 


Characteristics of Class Aves

  • Birds are warm-blooded animals.
  • Their forelimbs are modified into wings.
  • They have well-developed flight muscles that help during the flight.
  • Their hind limbs are adapted for walking, hopping, perching, grasping, wading and swimming.
  • There are epidermal scales on their legs.
  • The endoskeleton is bony with long hollow bones filled with air cavities. known as pneumatic bones.
  • Their spindle-shaped body minimizes resistance of the wind.
  • The feathers help in preventing heat loss and reduce air friction by providing passage to the air.
  • There is no skin gland except the oil gland.
  • The lower and upper and jaws are modified into a beak.
  • They have no teeth.
  • They have sharp eyesight.
  • The alimentary canal has a crop and a gizzard. The crops help in softening food, and the gizzard helps in crushing the food.
  • Pigeons and other seed-eating birds lack a gall bladder.
  • They have spongy and elastic lungs for respiration.
  • The special vocal organ called syrinx is present at the base of trachea.
  • Their heart is four-chambered.
  • RBCs are oval, nucleated and biconvex.
  • 12 pairs of cranial nerves are present.
  • They have a single ovary and oviduct on the left side
  • All the birds are oviparous and exhibit sexual dimorphism. The eggs have four embryonic membranes- amnion, chorion,  allantois, and yolk sac.

Classification of Class Aves

The class Aves is divided into two categories:


This class of birds are extinct. They had a toothed beak with a long lizard-like tail.

Eg., Archaeopteryx


These include extant as well as extinct birds. They have no teeth and a short tail.

Eg., Penguin, Grey Heron, Kingfisher, Duck, etc.

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By Team Learning Mantras