It is likely that birds evolved from reptiles. Like reptiles but unlike most mammals, they lay eggs that hatch outside the mother. All adult birds have feathers, rather than fur or scales, and most can fly. However, birds are similar to mammals in being warsm blooded.
When one thinks of the differences between mammals and birds, the first thing that comes to mind is that mammals give birth to their young whereas birds lay eggs. Now let us look at other differences between mammals and birds. The birds have feathers whereas mammals have only fur or hair. This feature is one of the main features of birds that differentiate them from mammals. Birds use feathers for controlling body temperature, flying, and attracting the opposite sex.
As birds need to fly, they have porous or hollow bones. In contrast, mammals have denser bones. Birds have wings although mammals have paws, hands, and hooves. There is also a difference in the feeding of the young. Mammals feed their young milk produced by the mammary glands. On the other hand, young birds are fed by the parents regurgitating partially digested food.
Birds and mammals have a larynx. The mammals produce sounds using the larynx. In birds, this organ does not produce sounds. Instead of using the larynx for sound, birds have a syrinx which serves as a voice box. The lungs of birds do not expand or contract as that of the lungs of mammals. In mammals, the oxygen and carbon dioxide is exchanged in the alveoli which are microscopic sacs in the lungs. In birds, the exchange happens in air capillaries which are walls of microscopic tubules. While there is only a single respiratory cycle in mammals, there are two cycles in birds.
Now comparing the blood, birds have a nucleus in the RBS whereas it is not generally seen in mammals. If there is a nucleus in the RBS in mammals, then it is a sign of sickness. The RBS of birds are oval in shape whereas most of the mammals’ RBSs have a round shape.
Picture Credit : Google