Birds have feathers
The feathers of birds trap air, which reduces the amount of heat lost from their bodies to cold surroundings!
Birds breathe through lungs
Although both mammals and birds breathe through lungs, the lungs of birds are different from those of mammals!
Birds lay eggs with hard shells
It is not surprising that the largest bird, the ostrich, lays the biggest eggs! The eggs of birds are covered in a hard shell to protect the developing chick inside the egg.