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

(N/A) Warm-blooded animals,such as birds and mammals,maintain a constant body temperature by cooling themselves in hotter environments and warming their bodies in cooler environments.
This process requires a significant amount of energy,which is generated through cellular respiration.
To support high rates of cellular respiration,these animals require a constant and efficient supply of oxygen $(O_2)$.
Separating oxygenated and deoxygenated blood ensures that the circulatory system functions at maximum efficiency,preventing the mixing of blood and ensuring that oxygen-rich blood is delivered effectively to all tissues to meet their high energy demands for thermoregulation.