Respuesta :
The respiratory system of birds is more efficient than that of mammals because:
Mammals: fresh air is mixed with oxygen-depleted air.
Birds: fresh air is NEVER mixed with oxygen-depleted air.
Birds' respiratory systems are among the most efficient. Nares are found in birds, whereas nostrils are found in mammals. Birds have air sacs in front and behind their lungs, whereas mammals have air sacs inside their lungs. Birds inhale and exhale twice for each respiration, whereas mammals only inhale and exhale once.
The avian lung has a flow-through system with small air capillaries, whereas the mammalian lung has reciprocating air circulation with large terminal air spaces (alveoli). As a result, the pulmonary capillary environment differs greatly between mammals and birds.
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