Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Warm-blooded animals such as birds and mammals maintain a constant body temperature by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment. Hence, these animals require more oxygen (O2) for more cellular respiration so that they can produce more energy to maintain their body temperature. Maintenance of optimum body temperature is called thermo-regulation, regulated by the hypothalamus in the brain.
Thus, it is necessary to separate oxygenated and deoxygenated blood.