Which outcome directly limits long-duration high-altitude avian flight when air sacs cannot fully inflate?

💡 Explanation

When air sacs are restricted, oxygen partial pressure gradient decreases because pulmonary blood flow is shunted away from poorly ventilated regions, thus dropping gas diffusion efficiency at altitude when the air is already thin during flight. Therefore, lower oxygen uptake results, rather than temperature, lift, or disease, which depend a variety of mechanisms.s

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