The Aves belong to the phylum Chordata of the animal kingdom. It has about 9,000 species. Aves are adapted to fly. All the birds come in the class Aves. Members of this class exhibit one of the most beautiful and visually stunning features such as bright and contrasting colours, unique patterns and a wide variety of striking poses. They show courtship, parental care, nest building, and territorial behaviour.

Characteristics of Aves

  1. Birds are warm-blooded animals. Their forelimbs are modified into wings.
  2. The hind limbs are adapted for walking, perching, and swimming.
  3. There is no skin gland except the oil gland.
  4. The upper and lower jaws are modified into a beak. They have no teeth.
  5. Legs are modified for walking, hopping, grasping, perching, wading and swimming. There are epidermal scales on their legs.
  6. The alimentary canal has a crop and a gizzard. The crops help in softening food, and the gizzard helps in crushing the food.
  7. Some seed-eating birds do not have a gall bladder.
  8. They have spongy and elastic lungs for respiration.
  9. The voice is produced by a special organ, the syrinx.
  10. The heart is four-chambered. The RBCs are nucleated, oval, and biconvex.
  11. They have 12 pairs of cranial nerves.
  12. They have a sharp sight.
  13. The endoskeleton is bony with long hollow bones filled with air cavities.
  14. They have a single ovary and oviduct on the left side
  15. All the birds are oviparous and exhibit sexual dimorphism. The eggs have four embryonic membranes- chorion, amnion, allantois, and yolk sac.
  16. They have a spindle-shaped body to minimize resistance to the wind.
  17. The feathers allow the air to pass and reduce friction to a minimum.
  18. They have well-developed flight muscles that help during flight.

Also read: Animal Kingdom

Classification of 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.

Also read: Chordata

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