Class : Aves

The characteristic features of Aves (birds) are the presence of feathers and most of them can fly except flightless birds (e.g., Ostrich).


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Corvus (Crow) Columba (Pigeon) Psittacula (Parrot)
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Struthio (Ostrich) Pavo (Peacock) Aptenodytes (Penguin)

Body characteristics:

  • They have a streamlined body that helps them to fly.
  • The jaws are modified into beak. Teeth are absent. The beak has various shapes and size, adapted for different food habits.

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  • The body is covered by feathers.
  • The forelimbs are modified into wings. Flight muscles are well developed to assist the movement of wings.
  • The hind limbs generally have scales and are modified for walking, swimming or clasping the tree branches.
  • Skin is dry without glands except the oil gland at the base of the tail.
  • Voice box, called syrinx, is present.
  • Endoskeleton is fully ossified (bony). Bones are hollow and have air cavities (pneumatic). It makes the body light, adapted for flying.



  • The digestive tract of birds has additional chambers, the crop and gizzard.
  • Heart is completely fourchambered.
  • They are warm-blooded (homoiothermous) animals, i.e., they are able to maintain a constant body temperature.
  • Respiration is by lungs. Air sacs connected to lungs supplement respiration.

Reproduction: Sexes are separate. Fertilisation is internal. They are oviparous and development is direct. Eggs have a calcareous shell.



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