Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Explanation

The mammals and birds are warm blooded animals which have high energy needs because they constantly require energy to maintain their body temoerature. It is necessary to separate oxygenated blood and deoxygenated blood in mammals and birds because such a separation allows a highly efficient supply of oxygen to the body cells which is required for producing a lot of energy needed by them.