Answer:
- The body is covered with feathers, and the forelimbs are modified into wings for flight. The bones are hollow (pneumatic), which makes the body light.
- They are warm-blooded (homoiothermous); the heart is four-chambered and respiration takes place by lungs with air sacs.
- The jaws are modified into a beak without teeth; they lay eggs with a hard calcareous shell and the body has a dry skin with scales on the legs.
Examples: pigeon, crow, sparrow, ostrich.